Showing 1–50 of 131 results for author: Zhou, X

Modification of $Υ$ production in $p$O and OO collisions at LHCb

Authors: LHCb collaboration, R. Aaij, M. Abdelfatah, A. S. W. Abdelmotteleb, C. Abellan Beteta, F. Abudinén, T. Ackernley, A. A. Adefisoye, B. Adeva, M. Adinolfi, P. Adlarson, C. Agapopoulou, C. A. Aidala, S. Akar, K. Akiba, H. Al Saleh, P. Albicocco, J. Albrecht, R. Aleksiejunas, F. Alessio, P. Alvarez Cartelle, S. Amato, J. L. Amey, Y. Amhis, Z. Amos , et al. (1166 additional authors not shown)

Abstract: The production rates of $\mathitΥ(2S)$ and $\mathitΥ(3S)$ mesons relative to that of the $\mathitΥ(1S)$ state are measured in $pp$, $p$O, and OO collisions by the LHCb collaboration. The ratios measured in $pp$ data are consistent with previous LHCb measurements at different center-of-mass energies. Only slight relative suppression of the $\mathitΥ(2S)$ and $\mathitΥ(3S)$ states is found in $p$O c… ▽ More The production rates of $\mathitΥ(2S)$ and $\mathitΥ(3S)$ mesons relative to that of the $\mathitΥ(1S)$ state are measured in $pp$, $p$O, and OO collisions by the LHCb collaboration. The ratios measured in $pp$ data are consistent with previous LHCb measurements at different center-of-mass energies. Only slight relative suppression of the $\mathitΥ(2S)$ and $\mathitΥ(3S)$ states is found in $p$O collisions, while in OO collisions the $\mathitΥ(2S)$ is suppressed by a factor of $\sim2$, with evidence for suppression of the $\mathitΥ(3S)$. The significant suppression in OO data, compared to the small effect in $p$O data, shows the emergence of additional suppression mechanisms in the relatively small OO collision system. Models incorporating quark-gluon plasma formation in OO collisions successfully describe the data. Implications for the interplay between cold nuclear matter effects and color screening in a deconfined quark-gluon plasma are discussed. △ Less

Submitted 31 July, 2026; originally announced August 2026.

Comments: All figures and tables, along with machine-readable versions and any supplementary material and additional information, are available at https://lhcb-glance.cern.ch/alcm/public/analysis/full-details/6994/ (LHCb public pages)

Report number: LHCb-PAPER-2026-027, CERN-EP-2026-207

Measurement of the average transverse momentum of forward prompt charged particles in $pp$ and $p\mathrm{Pb}$ collisions at $\sqrt{s_{NN}} = 5.02\; \mathrm{TeV}$

Authors: LHCb collaboration, R. Aaij, M. Abdelfatah, A. S. W. Abdelmotteleb, C. Abellan Beteta, F. Abudinén, T. Ackernley, A. A. Adefisoye, B. Adeva, M. Adinolfi, P. Adlarson, C. Agapopoulou, C. A. Aidala, S. Akar, K. Akiba, P. Albicocco, J. Albrecht, R. Aleksiejunas, F. Alessio, P. Alvarez Cartelle, S. Amato, J. L. Amey, Y. Amhis, L. An, L. Anderlini , et al. (1105 additional authors not shown)

Abstract: This letter presents the first measurements of the average transverse momentum of prompt charged particles in $pp$ and $p\mathrm{Pb}$ collisions as a function of collision multiplicity and pseudorapidity. The data were recorded at nucleon-nucleon centre-of-mass energy $\sqrt{s_{NN}} = 5.02\; \mathrm{TeV}$ with the LHCb experiment. The pseudorapidity dependence of the multiplicity distribution is a… ▽ More This letter presents the first measurements of the average transverse momentum of prompt charged particles in $pp$ and $p\mathrm{Pb}$ collisions as a function of collision multiplicity and pseudorapidity. The data were recorded at nucleon-nucleon centre-of-mass energy $\sqrt{s_{NN}} = 5.02\; \mathrm{TeV}$ with the LHCb experiment. The pseudorapidity dependence of the multiplicity distribution is also measured. The average transverse momentum results show a decreasing trend with pseudorapidity, more pronounced in high-multiplicity events, consistent with the collective behaviour of the produced matter. The measurements are reproduced by state-of-the-art (3+1D) hydrodynamic calculations, while saturation models are not compatible with the data. △ Less

Submitted 12 August, 2026; v1 submitted 29 July, 2026; originally announced July 2026.

Comments: All figures and tables, along with any supplementary material and additional information, are available at https://lhcb-glance.cern.ch/alcm/public/analysis/full-details/5570/ (LHCb public pages)

Report number: CERN-EP-2026-177, LHCb-PAPER-2026-012

Precision masses of neutron-rich platinum and gold nuclei reveal enhanced $N=126$ shell strength below doubly-magic $^{208}$Pb

Authors: David Freire-Fernández, Rui-Jiu Chen, Usama Ahmed, Helena M. Albers, Jelena Bardak, Carsten Brandau, Jeroen P. Bormans, R. Burcu Cakirli, Rikel Chakma, Maeve Cockshutt, Iris Dillmann, Dmytro Dmytriiev, Siddharth Doshi, Carlo Forconi, Oliver Forstner, Wenwen Ge, Jan Glorius, Magdalena Gòrska, Chris J. Griffin, Alexandre Gumberidze, Regina Hess, Pierre-Michel Hillenbrand, Nicolas J. Hubbard, Calum Jones, Beatriz Jurado , et al. (41 additional authors not shown)

Abstract: The heaviest stable nuclei in the universe owe their existence to quantum shell structure, the grouping of protons and neutrons into discrete energy levels separated by gaps. The largest known neutron shell gap in stable nuclei, at $N=126$, stabilizes doubly-magic $^{208}$Pb and is responsible for the characteristic abundance peak of heavy elements near gold and platinum produced by the rapid neut… ▽ More The heaviest stable nuclei in the universe owe their existence to quantum shell structure, the grouping of protons and neutrons into discrete energy levels separated by gaps. The largest known neutron shell gap in stable nuclei, at $N=126$, stabilizes doubly-magic $^{208}$Pb and is responsible for the characteristic abundance peak of heavy elements near gold and platinum produced by the rapid neutron-capture process (r-process). Whether this shell gap persists as protons are removed from lead is a question central to both nuclear structure and the modeling of heavy-element synthesis, yet it has remained unanswered due to the extraordinary difficulty of producing the relevant neutron-rich nuclei. Direct experimental knowledge in this region was essentially absent. Here we report the first precision mass measurements of $^{203,204}$Pt and $^{204,205,206}$Au, performed at GSI using a novel combination of Schottky and isochronous mass spectrometry in a heavy-ion storage ring. The $N=126$ isotones $^{204}$Pt and $^{205}$Au are more strongly bound than the extrapolated trend of the previously known mass surface by 403 and 464~keV, respectively, revealing an unexpectedly enhanced $N=126$ shell strength below doubly-magic $^{208}$Pb. Furthermore, the proton-neutron interaction strength exhibits a hitherto unobserved bifurcation at $N=126$ as protons are removed from $^{208}$Pb. Our results redefine the nuclear mass surface in the neutron-rich heavy-element region and provide direct experimental benchmarks for theoretical models whose extrapolations toward more exotic nuclei are essential for r-process nucleosynthesis calculations. △ Less

Submitted 12 July, 2026; originally announced July 2026.

Comments: 35 pages, 5 Figures, and Supplementary information. Submitted to Nature

Hyperon-Nucleon Spectrometer

Authors: Xiaozhi Bai, Xu Cao, Zhe Cao, Jinhui Chen, Kai Chen, Qibo Chen, Shi Chen, Xin Chen, Yuquan Chen, Zhenyu Chen, Jianping Dai, Heng-Tong Ding, Dongshuo Du, Shuxian Du, Limin Duan, Zhe Duan, Anhui Feng, Jie Feng, Yicheng Feng, Jinlin Fu, Xiaofeng Fu, Chaosong Gao, Liang Ge, Wenwen Ge, Lisheng Geng , et al. (215 additional authors not shown)

Abstract: Chirality lies at the heart of low-energy QCD, governing the symmetry structure that shapes hadron masses and strong interaction dynamics. Among the most compelling open questions tied to chiral dynamics and spontaneous chiral symmetry breaking is the longstanding $Λ$ polarization puzzle, in which $Λ$ hyperons produced in unpolarized hadronic collisions exhibit a surprisingly large transverse pola… ▽ More Chirality lies at the heart of low-energy QCD, governing the symmetry structure that shapes hadron masses and strong interaction dynamics. Among the most compelling open questions tied to chiral dynamics and spontaneous chiral symmetry breaking is the longstanding $Λ$ polarization puzzle, in which $Λ$ hyperons produced in unpolarized hadronic collisions exhibit a surprisingly large transverse polarization that remains theoretically unexplained. This whitepaper presents the proposal for the Hyperon-Nucleon Spectrometer (H-NS) at the High-Intensity heavy-ion Accelerator Facility (HIAF). Leveraging the high energy and high intensity of HIAF's proton and heavy-ion beams, the H-NS experiment will perform systematic studies of hyperon polarization phenomena and their underlying mechanisms in proton-proton ($pp$), proton-nucleus ($pA$), and nucleus-nucleus ($AA$) collisions in the fixed target mode. A wide-range beam energy scan, including proton beams from 3 GeV up to 9.3 GeV (HIAF) and up to 32 GeV (upgraded HIAF), will be conducted to examine the dependence of polarization on collision energy. The spectrometer is designed with specialized detectors capable of high-precision reconstruction of final-state baryon polarizations. Among its many interesting and important measurements, H-NS will simultaneously measure hyperon and proton spin observables to explore the polarization mechanism in hadronic interactions and the spin structure of baryons. Furthermore, the use of $pA$ and $AA$ collisions will enable detailed investigations of cold and hot nuclear matter effects on spin polarization. Its physics program and detector development will significantly benefit the future Electron-ion Collider in China. △ Less

Submitted 4 June, 2026; originally announced June 2026.

Comments: 69 pages, Hyperon-Nucleon Spectrometer (H-NS) white paper

Search for $Ξ^0p$, $Ω^- p$, and $Ω^- n$ dibaryons in $Υ(1S)$ and $Υ(2S)$ decays at Belle

Authors: Belle, Belle II Collaborations, :, M. Abumusabh, I. Adachi, A. Aggarwal, Y. Ahn, H. Aihara, N. Akopov, S. Alghamdi, M. Alhakami, N. Althubiti, K. Amos, N. Anh Ky, H. Atmacan, V. Aushev, R. Ayad, V. Babu, H. Bae, N. K. Baghel, P. Bambade, Sw. Banerjee, M. Bartl, J. Baudot, A. Beaubien , et al. (345 additional authors not shown)

Abstract: We search for $Ξ^0p$, $Ω^-p$, and $Ω^-n$ dibaryon states in $Υ(1S)$ and $Υ(2S)$ decays, probing mass regions near the corresponding baryon-pair thresholds. Multistrange baryon-baryon interactions are relevant to neutron-star matter but remain largely unconstrained. Experimental and theoretical studies supporting attractive $ΞN$ and $ΩN$ interactions, where $N$ denotes a nucleon, motivate searches… ▽ More We search for $Ξ^0p$, $Ω^-p$, and $Ω^-n$ dibaryon states in $Υ(1S)$ and $Υ(2S)$ decays, probing mass regions near the corresponding baryon-pair thresholds. Multistrange baryon-baryon interactions are relevant to neutron-star matter but remain largely unconstrained. Experimental and theoretical studies supporting attractive $ΞN$ and $ΩN$ interactions, where $N$ denotes a nucleon, motivate searches for weakly bound states. We use samples of $102$ million $Υ(1S)$ and $158$ million $Υ(2S)$ decays collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. No significant signals are observed, and the first $90$% confidence-level upper limits are set on the branching fractions of $Υ(1S)$ and $Υ(2S)$ decays to $Ξ^0p$, $Ω^-p$, and $Ω^-n$ dibaryon states, at the level of $O(10^{-7})$-$O(10^{-6})$, depending on the channel and the assumed mass difference from the corresponding baryon-pair threshold. △ Less

Submitted 17 July, 2026; v1 submitted 28 May, 2026; originally announced May 2026.

Comments: Revised author list according to the Belle II author-list policy, including ORCID IDs and without listing institutions; no changes to the scientific content

Study of nuclear effects on charm production in light-ion collisions

Authors: LHCb collaboration, R. Aaij, M. Abdelfatah, A. S. W. Abdelmotteleb, C. Abellan Beteta, F. Abudinén, T. Ackernley, A. A. Adefisoye, B. Adeva, M. Adinolfi, P. Adlarson, C. Agapopoulou, C. A. Aidala, S. Akar, K. Akiba, P. Albicocco, J. Albrecht, R. Aleksiejunas, F. Alessio, P. Alvarez Cartelle, S. Amato, J. L. Amey, Y. Amhis, L. An, L. Anderlini , et al. (1105 additional authors not shown)

Abstract: The onset of nuclear effects in light-ion collisions is studied by measuring the ratio of $D^0$ meson production between NeNe and OO collisions at a center-of-mass energy per nucleon pair of $5.36\,{\rm TeV}$ recorded by the LHCb detector. The $D^0$ meson yields are measured differentially in transverse momentum ($p_{\rm T}$) for $0.5<p_{\rm T}<20\,{\rm GeV}$ in the rapidity ($y$) region… ▽ More The onset of nuclear effects in light-ion collisions is studied by measuring the ratio of $D^0$ meson production between NeNe and OO collisions at a center-of-mass energy per nucleon pair of $5.36\,{\rm TeV}$ recorded by the LHCb detector. The $D^0$ meson yields are measured differentially in transverse momentum ($p_{\rm T}$) for $0.5<p_{\rm T}<20\,{\rm GeV}$ in the rapidity ($y$) region $2.0<y<4.5$, and are normalized to the total number of recorded inelastic nucleus-nucleus collisions in each data sample. The resulting production ratio shows evidence of variation as a function of $p_{\rm T}$, which is inconsistent with predictions based on nuclear modification of nucleon structure alone. This measurement is consistent with the onset of quark-gluon plasma production with increasing nucleus size in high-energy nuclear collisions. △ Less

Submitted 26 May, 2026; originally announced May 2026.

Comments: All figures and tables, along with machine-readable versions and any supplementary material and additional information, are available at https://lbfence.cern.ch/alcm/public/analysis/full-details/6142/ (LHCb public pages)

Report number: LHCb-PAPER-2026-008, CERN-EP-2026-141

Study of $\barΛ$-$p$ Annihilation into Light Mesons

Authors: BESIII Collaboration, M. Ablikim, M. N. Achasov, P. Adlarson, X. C. Ai, C. S. Akondi, R. Aliberti, A. Amoroso, Q. An, Y. H. An, Y. Bai, O. Bakina, H. -R. Bao, X. L. Bao, M. Barbagiovanni, V. Batozskaya, K. Begzsuren, N. Berger, M. Berlowski, M. B. Bertani, D. Bettoni, F. Bianchi, E. Bianco, A. Bortone, I. Boyko , et al. (736 additional authors not shown)

Abstract: The annihilation of $\barΛ$-$p$ into light mesons is studied using $(10.087\pm0.044)\times10^{9}$ $J/ψ$ events collected with the BESIII detector at the BEPCII storage ring. The $\barΛ$ baryons are produced in the process $J/ψ\rightarrowΛ\barΛ$ and interact with the protons in the hydrogen nuclei in the cooling oil of the beam pipe. The reactions $\barΛp\rightarrow K^+π^+π^-$ and $K^+2π^+2π^-$ are… ▽ More The annihilation of $\barΛ$-$p$ into light mesons is studied using $(10.087\pm0.044)\times10^{9}$ $J/ψ$ events collected with the BESIII detector at the BEPCII storage ring. The $\barΛ$ baryons are produced in the process $J/ψ\rightarrowΛ\barΛ$ and interact with the protons in the hydrogen nuclei in the cooling oil of the beam pipe. The reactions $\barΛp\rightarrow K^+π^+π^-$ and $K^+2π^+2π^-$ are observed for the first time, evidence for the reaction $\barΛp\rightarrow K^0_S2π^+π^-$ is found, and no significant signals are seen for the reactions $\barΛp\rightarrow K^0_Sπ^+$, $K^+3π^+3π^-$ and $2K^+K^-$. The cross sections of these reactions are also measured at $P_{\barΛ}\approx 1.074$ GeV/$c$. Furthermore, no significant structures are observed in the combinations of the final state particles for these reactions. The annihilation of $\barΛ$-$p$ into light mesons presents the similar behavior as $\bar{n}$-$p$ reactions in this energy region. These new measurements will serve as important inputs for the theoretical understanding of the antihyperon-nucleon interaction, and further contribute to understanding antibaryon-baryon interaction in a unified perspective. △ Less

Submitted 4 February, 2026; originally announced February 2026.

Comments: 9 pages, 2 figures

Observation of $\barΛp\to K^{+}π^{+}π^{-}π^{0}$ and $\barΛp\to K^{+}π^{+}π^{-}2π^{0}$

Authors: BESIII Collaboration, M. Ablikim, M. N. Achasov, P. Adlarson, X. C. Ai, C. S. Akondi, R. Aliberti, A. Amoroso, Q. An, Y. H. An, Y. Bai, O. Bakina, Y. Ban, H. -R. Bao, X. L. Bao, V. Batozskaya, K. Begzsuren, N. Berger, M. Berlowski, M. B. Bertani, D. Bettoni, F. Bianchi, E. Bianco, A. Bortone, I. Boyko , et al. (728 additional authors not shown)

Abstract: Using $(10087 \pm 44) \times 10^6$ $J/ψ$ events collected with the BESIII detector at a center-of-mass energy of $\sqrt{s}=3.097$ GeV, the antihyperon-nucleon annihilation processes $\barΛ p \to K^+ π^+ π^- + kπ^0$ ($k=1,2,3$) are studied at an incident $\barΛ$ momentum of approximately 1.074 GeV/$c$. The reactions $\barΛ p \to K^+ π^+ π^- π^0$ and $\barΛ p \to K^+ π^+ π^- 2π^0$ are observed for t… ▽ More Using $(10087 \pm 44) \times 10^6$ $J/ψ$ events collected with the BESIII detector at a center-of-mass energy of $\sqrt{s}=3.097$ GeV, the antihyperon-nucleon annihilation processes $\barΛ p \to K^+ π^+ π^- + kπ^0$ ($k=1,2,3$) are studied at an incident $\barΛ$ momentum of approximately 1.074 GeV/$c$. The reactions $\barΛ p \to K^+ π^+ π^- π^0$ and $\barΛ p \to K^+ π^+ π^- 2π^0$ are observed for the first time, with corresponding cross sections $σ_{\barΛ p \to K^+ π^+ π^- π^0} = 8.5^{+1.2}_{-1.1} (\rm{stat.}) \pm 0.4 (\rm {syst.})$ mb and $σ_{\barΛ p \to K^+ π^+ π^- 2π^0} = 7.9^{+1.9}_{-1.7} \pm 0.4$ mb. No significant signal is found for $\barΛ p \to K^+ π^+ π^- 3π^0$, and an upper limit of 7.2 mb is set at a 90\% confidence level. An evidence for the $K^{*}(892)^+$ resonance is seen in the $K^+π^0$ invariant mass spectrum $M_{K^+π^0}$ for $k=1$, and the corresponding cross section for $\barΛ p \to K^{*}(892)^+ π^+ π^-$ is measured to be $σ_{\barΛ p \to K^{*}(892)^+ π^+ π^-} = 12.5^{+3.8}_{-3.4} \pm 1.2$ mb. Owing to the limited statistics, possible interference effects are not considered. These findings offer crucial input to deepen our understanding of the antihyperon-nucleon interactions. △ Less

Submitted 15 April, 2026; v1 submitted 1 February, 2026; originally announced February 2026.

Journal ref: Phys. Rev. Lett. 136, 171904 (2026)

Precise $^{136}$Xe Double Beta Decay Measurement in PandaX-4T with Implications on the Nuclear Matrix Elements and Majorons

Authors: PandaX Collaboration, Zhe Yuan, Zihao Bo, Wei Chen, Xun Chen, Yunhua Chen, Chen Cheng, Xiangyi Cui, Manna Deng, Yingjie Fan, Deqing Fang, Xuanye Fu, Zhixing Gao, Yujie Ge, Lisheng Geng, Karl Giboni, Xunan Guo, Xuyuan Guo, Zichao Guo, Chencheng Han, Ke Han, Changda He, Jinrong He, Houqi Huang, Junting Huang , et al. (89 additional authors not shown)

Abstract: The continuous spectrum of double beta decay ($ββ$) provides a sensitive probe to test the predictions of the standard model and to search for signatures of new physics beyond it. We present a comprehensive analysis of the $^{136}$Xe $ββ$ spectrum utilizing $39.1 \pm 0.7~\textrm{kg}\cdot\textrm{yr}$ of $^{136}$Xe exposure from the PandaX-4T experiment. The analysis yields the most precise measurem… ▽ More The continuous spectrum of double beta decay ($ββ$) provides a sensitive probe to test the predictions of the standard model and to search for signatures of new physics beyond it. We present a comprehensive analysis of the $^{136}$Xe $ββ$ spectrum utilizing $39.1 \pm 0.7~\textrm{kg}\cdot\textrm{yr}$ of $^{136}$Xe exposure from the PandaX-4T experiment. The analysis yields the most precise measurement to date of the $^{136}$Xe two-neutrino double beta decay ($2νββ$) half-life, $(2.14 \pm 0.05) \times 10^{21}$ years, the uncertainty of which is reduced by a factor of 2 compared to our previous result. We measure the parameter $ξ_{31}^{2ν}$, defined as the ratio between the subleading and leading components of the $^{136}$Xe $2νββ$ nuclear matrix element, to be $0.59^{+0.41}_{-0.38}$, which is consistent with theoretical predictions. We also search for Majoron-emitting modes of $^{136}$Xe $ββ$, establishing the most stringent limit for the spectral index $n=7$. △ Less

Submitted 9 April, 2026; v1 submitted 4 December, 2025; originally announced December 2025.

Comments: 8 pages, 4 figures

Journal ref: Phys. Rev. Lett. 136, 162501 (2026)

Experimental study of the reaction $Ξ^{0}n\rightarrowΛΛX$ using $Ξ^{0}$-nucleus scattering

Authors: BESIII Collaboration, M. Ablikim, M. N. Achasov, P. Adlarson, X. C. Ai, R. Aliberti, A. Amoroso, Q. An, Y. Bai, O. Bakina, Y. Ban, H. -R. Bao, V. Batozskaya, K. Begzsuren, N. Berger, M. Berlowski, M. Bertani, D. Bettoni, F. Bianchi, E. Bianco, A. Bortone, I. Boyko, R. A. Briere, A. Brueggemann, H. Cai , et al. (707 additional authors not shown)

Abstract: Using $(10087\pm44)\times10^{6}$$J/ψ$ events collected with the BESIII detector operating at the BEPCII storage ring in $2009$, $2012$, $2018$, and $2019$, we perform a search for the reaction $Ξ^0n\rightarrowΛΛX$, where $X$ denotes any additional final particles. Given the highly suppressed phase space for producing extra pions, the $X$ consists of either nothing or a photon, corresponding to the… ▽ More Using $(10087\pm44)\times10^{6}$$J/ψ$ events collected with the BESIII detector operating at the BEPCII storage ring in $2009$, $2012$, $2018$, and $2019$, we perform a search for the reaction $Ξ^0n\rightarrowΛΛX$, where $X$ denotes any additional final particles. Given the highly suppressed phase space for producing extra pions, the $X$ consists of either nothing or a photon, corresponding to the processes $Ξ^0 n \rightarrow ΛΛ$ and $Ξ^{0}n\rightarrowΛΣ^0\rightarrowΛΛγ$. The $Ξ^0$ comes from the decay of $J/ψ\rightarrowΞ^0\barΞ^0$, while the neutron originates from material of the beam pipe. A signal is observed for the first time with a statistical significance of 6.4$σ$. The cross section for the reaction $Ξ^0+{^9\rm{Be}}\rightarrowΛ+Λ+X$ is measured to be $(43.6\pm10.5_{\text{stat}}\pm11.1_{\text{syst}})$ mb at $P_{Ξ^0}\approx0.818$ GeV/$c$, where the first uncertainty is statistical and the second systematic. No significant $H$-dibaryon signal is observed in the $ΛΛ$ final state. △ Less

Submitted 26 February, 2026; v1 submitted 4 December, 2025; originally announced December 2025.

Comments: 9 pages, 3 figures

Baryon-antibaryon photoproduction cross sections off the proton

Authors: GlueX Collaboration, F. Afzal, M. Albrecht, M. Amaryan, S. Arrigo, V. Arroyave, A. Asaturyan, A. Austregesilo, Z. Baldwin, F. Barbosa, J. Barlow, E. Barriga, R. Barsotti, D. Barton, V. Baturin, V. V. Berdnikov, A. Berger, W. Boeglin, M. Boer, W. J. Briscoe, T. Britton, R. Brunner, S. Cao, C. Chen, E. Chudakov , et al. (115 additional authors not shown)

Abstract: The GlueX experiment at Jefferson Lab has observed $p\bar{p}$ and, for the first time, $Λ\barΛ$ and $p\barΛ$ photoproduction from a proton target at photon energies up to 11.6 GeV. The angular distributions are forward peaked for all produced pairs, consistent with Regge-like $t$-channel exchange. Asymmetric wide-angle anti-baryon distributions show the presence of additional processes. In a pheno… ▽ More The GlueX experiment at Jefferson Lab has observed $p\bar{p}$ and, for the first time, $Λ\barΛ$ and $p\barΛ$ photoproduction from a proton target at photon energies up to 11.6 GeV. The angular distributions are forward peaked for all produced pairs, consistent with Regge-like $t$-channel exchange. Asymmetric wide-angle anti-baryon distributions show the presence of additional processes. In a phenomenological model, we find consistency with a double $t$-channel exchange process where anti-baryons are created only at the middle vertex. The model matches all observed distributions with a small number of free parameters. In the hyperon channels, we observe a clear distinction between photoproduction of the $Λ\barΛ$ and $p\barΛ$ systems but general similarity to the $p\bar{p}$ system. We report both total cross sections and cross sections differential with respect to momentum transfer and the invariant masses of the created particle pairs. No narrow resonant structures were found in these reaction channels. The suppression of $s\bar{s}$ quark pairs relative to $d\bar{d}$ quark pairs is similar to what has been seen in other reactions. △ Less

Submitted 10 May, 2026; v1 submitted 30 October, 2025; originally announced October 2025.

Comments: 34 pages, 29 figures, 7 tables, 1 algorithm

Journal ref: Phys. Rev. C 113, 045207 (2026)

Tomographic beta-gamma spectroscopy of nuclear beta decay

Authors: PandaX Collaboration, Zhe Yuan, Zihao Bo, Wei Chen, Xun Chen, Yunhua Chen, Chen Cheng, Xiangyi Cui, Manna Deng, Yingjie Fan, Deqing Fang, Xuanye Fu, Zhixing Gao, Yujie Ge, Lisheng Geng, Karl Giboni, Xunan Guo, Xuyuan Guo, Zichao Guo, Chencheng Han, Ke Han, Changda He, Jinrong He, Houqi Huang, Junting Huang , et al. (89 additional authors not shown)

Abstract: Nuclear $β$ decay, a sensitive probe of nuclear structure and weak interactions, has become a precision test bed for physics beyond the Standard Model, driven by recent advances in spectrometric techniques. Here we introduce tomographic $β$-$γ$ spectroscopy (TBGS) of nuclear $β$ decay, a method that detects the energies of $β$, $γ$, and internal conversion electrons while simultaneously reconstruc… ▽ More Nuclear $β$ decay, a sensitive probe of nuclear structure and weak interactions, has become a precision test bed for physics beyond the Standard Model, driven by recent advances in spectrometric techniques. Here we introduce tomographic $β$-$γ$ spectroscopy (TBGS) of nuclear $β$ decay, a method that detects the energies of $β$, $γ$, and internal conversion electrons while simultaneously reconstructing the energy deposition vertices. Using the PandaX-4T detector operated as a TBGS, we obtain a precise and unbiased decay scheme of $^{214}$Pb, a key background isotope in searches for dark matter and Majorana neutrinos. For the first time, transitions of $^{214}$Pb to both the ground and excited states of $^{214}$Bi are measured concurrently, revealing discrepancies in branching ratios of up to 4.7$σ$ relative to previous evaluations. Combined with state-of-the-art theoretical spectral-shape calculations, these results establish a new benchmark for background modelling in rare-event searches and highlight the potential of TBGS as a versatile tool for fundamental physics and nuclear applications. △ Less

Submitted 29 November, 2025; v1 submitted 28 October, 2025; originally announced October 2025.

Threshold $J/ψ$ Photoproduction as a Probe of Nuclear Gluon Structure

Authors: J. R. Pybus, D. Dutta, H. Gao, O. Hen, I. Korover, T. Kolar, A. Schmidt, A. Somov, H. Szumila-Vance, D. Androić, C. Ayerbe Gayoso, X. Bai, V. V. Berdnikov, S. Bhattarai, Z. Chen, E. O. Cohen, O. Cortes Becerra, K. Dehmelt, A. Deur, B. R. Devkota, L. Ehinger, L. El Fassi, S. Fang, P. Gautam, J. -O. Hansen , et al. (62 additional authors not shown)

Abstract: The nuclear EMC effect is the observation that quark distributions in bound nucleons experience significant modification at large $x$ relative to free nucleons. Despite decades of measurements verifying the presence of this effect in quarks across a wide range of nuclei, behavior of large-$x$ gluons in nuclei remains almost completely unknown. As the nuclear physics community seeks out new observa… ▽ More The nuclear EMC effect is the observation that quark distributions in bound nucleons experience significant modification at large $x$ relative to free nucleons. Despite decades of measurements verifying the presence of this effect in quarks across a wide range of nuclei, behavior of large-$x$ gluons in nuclei remains almost completely unknown. As the nuclear physics community seeks out new observables to try to elucidate the mechanisms behind the EMC effect, it becomes striking that we remain ignorant regarding the impact of nuclear effects on gluonic behavior. Recent photonuclear data using the Hall D photon beam have enabled the first measurement of $J/ψ$ photoproduction from nuclei near and below the energy threshold, with the results highlighted in Physical Review Letters as an Editors' Suggestion. These data have placed the first, and currently only, constraints on the behavior of large-$x$ gluons within bound nucleons. However, compared to the quantity of data which currently informs our knowledge of the quark-sector EMC effect, these data are extremely limited, and remain unable to conclusively observe or exclude large modification of gluon distributions. A high-luminosity photonuclear experiment will enable a precision measurement of incoherent $J/ψ$ photoproduction at and below the threshold region. This data will provide the first stringent constraints on nuclear modification of gluon structure or other exotic effects which could impact the production of $J/ψ$ from nuclei. We request 85 PAC days at Hall D using the GlueX detector with a 12 GeV electron beam energy and a coherent photon peak energy of $8$ GeV, split into 80 days using a $^4$He target and 5 calibration days using a $^2$H target. △ Less

Submitted 24 October, 2025; originally announced October 2025.

Comments: 26 pages, 12 figures, porposal for Jefferson Lab Experiment E12-25-002, submitted to Jefferson Lab PAC 53 (2025)

Precision measurement and modelling of the threshold-free 210Pb β spectrum

Authors: Shuo Zhang, Hao-Ran Liu, Ke Han, Xavier Mougeot, Paul-Antoine Hervieux, Tao Sun, Wen-Tao Wu, Robin Cantor, Jing-Kai Xia, Zhi Liu, Jun-Cheng Liang, Fu-You Fan, Le Zhang, Ming-Yu Ge, Xiao-Peng Zhou, Adrien Andoche

Abstract: Beta decay is a fundamental process that governs nuclear stability and serves as a sensitive probe of the weak interaction and possible physics beyond the Standard Model of particle physics. However, precise measurements of complete $β$ decay spectra, particularly at low energies, remain experimentally and theoretically challenging. Here we report a high-precision, threshold-free measurement of th… ▽ More Beta decay is a fundamental process that governs nuclear stability and serves as a sensitive probe of the weak interaction and possible physics beyond the Standard Model of particle physics. However, precise measurements of complete $β$ decay spectra, particularly at low energies, remain experimentally and theoretically challenging. Here we report a high-precision, threshold-free measurement of the full $β$ decay spectrum of 210Pb to excited states of 210Bi, using a transition-edge sensor (TES)-based micro-calorimeter. This approach enables the detection of $β$ particle energies from 0 keV up to their endpoint by coincidence summing with subsequent de-excitation energy, thereby eliminating reconstruction artifacts near zero energy that have traditionally limited low-energy spectral accuracy. To our knowledge, this is the first complete, high-precision $β$ decay spectrum from 0 keV. The data resolve theoretical uncertainties associated with the atomic quantum exchange (AQE) effect. An accompanying ab initio theoretical framework, incorporating atomic, leptonic, and nuclear components, predicts a statistically significant (7.2 {$σ$}) enhancement in $β$ emission probability near zero energy, in agreement with the measurement and in contrast to models that omit AQE corrections. These results provide a new benchmark for $β$ decay theory at low energies, deepen our understanding of the weak interaction, and establish a critical foundation for searches for new physics, including dark matter interactions and precision studies of neutrinos. △ Less

Submitted 1 October, 2025; v1 submitted 30 September, 2025; originally announced September 2025.

Comments: 14 pages, 7 figures

A novel method of half-life determination for highly charged ions based on isochronous mass spectrometry

Authors: Qi Zeng, Bushi Huang, Tingwei Peng, Hongfu Li, Xing XuYuanming Xing, Huaiqiang Zhang, Jiankun Zhao, Xu Zhou

Abstract: The lifetime of the isomeric state in fully stripped 94Ru44+ ions has been measured using isochronous mass spectrometry (IMS) at the experimental Cooler Storage Ring (CSRe) of the Heavy Ion Research Facility in Lanzhou (HIRFL). Previously, the isomeric lifetime was determined by analyzing the decay time points of individual decay events. In this paper, we present a novel approach to determine the… ▽ More The lifetime of the isomeric state in fully stripped 94Ru44+ ions has been measured using isochronous mass spectrometry (IMS) at the experimental Cooler Storage Ring (CSRe) of the Heavy Ion Research Facility in Lanzhou (HIRFL). Previously, the isomeric lifetime was determined by analyzing the decay time points of individual decay events. In this paper, we present a novel approach to determine the isomeric lifetime based on the survival time of ions obtained from IMS. The survival lifetimes of the ground and isomeric states of 94Ru44+ were measured to be s and s in the laboratory, respectively. Given that the ground state of 94Ru44+ has a natural lifetime of approximately 75 min, its survival lifetime in the experimental setup was predominantly determined by the beam-loss lifetime, including interactions with residual gas in the storage ring and carbon foil of the detector. In contrast, the survival lifetime of 94mRu44+ was governed by its intrinsic nuclear lifetime and additional beam-loss effects. The nuclear decay lifetime of 94mRu44+ was extracted through differential survival lifetime analysis between ground and isomeric states, under the assumption that the beam-loss lifetimes for both quantum systems are identical. Using this novel methodology, the lifetime measured in the laboratory frame was s. After relativistic time-dilation corrections, the corresponding rest-frame half-life was calculated to be s. This result demonstrates excellent consistency with previous experimental results, validating the reliability of the new method. This method is suitable for determining half-lives of highly charged ions in the range of several tens of microseconds to milliseconds using IMS. △ Less

Submitted 19 September, 2025; originally announced September 2025.

Comments: to be published in Chinese Physics C

Journal ref: Chin. Phys. C 2025,49(11):114002

A high-lying isomer in ^{92}Zr with lifetime modulated by the atomic charge states: a proposed approach for a nuclear gamma-ray laser

Authors: C. X. Jia, S. Guo, B. Ding, X. H. Zhou, C. X. Yuan, W. Hua J. G. Wang, S. W. Xu, C. M. Petrache, E. A. Lawrie, Y. B. Wu, Y. D. Fang, Y. H. Qiang, Y. Y. Yang, J. B. Ma, J. L. Chen, H. X. Chen, F. Fang, Y. H. Yu, B. F. Lv, F. F. Zeng, Q. B. Zeng, H. Huang, Z. H. Jia, W. Liang, W. Q. Zhang , et al. (23 additional authors not shown)

Abstract: The nuclides ^{92}Zr are produced and transported by using a radioactive beam line to a lowbackground detection station. After a flight time of about 1.14 μs, the ions are implanted into a carbon foil, and four γ rays deexciting the 8+ state in ^{92}Zr are observed in coincidence with the implantation signals within a few nanoseconds. We conjecture that there exists an isomer located slightly abov… ▽ More The nuclides ^{92}Zr are produced and transported by using a radioactive beam line to a lowbackground detection station. After a flight time of about 1.14 μs, the ions are implanted into a carbon foil, and four γ rays deexciting the 8+ state in ^{92}Zr are observed in coincidence with the implantation signals within a few nanoseconds. We conjecture that there exists an isomer located slightly above the 8^{+} state in ^{92}Zr. The isomeric lifetime in highly charged states is extended significantly due to the blocking of internal conversion decay channels, enabling its survival over the transportation. During the slowing-down process in the carbon foil, the ^{92}Zr ions capture electron and evolve toward neutral atoms, and consequently the lifetime is restored to a normal short value. Such a high-lying isomer depopulated by a low-energy transition may provide unique opportunity to develop nuclear γ laser. △ Less

Submitted 3 September, 2025; originally announced September 2025.

Measurement of transverse $Λ$ and $\barΛ$ hyperon polarization in $p$Pb collisions at $\sqrt{s_{NN}} = 5.02$ TeV

Authors: LHCb collaboration, R. Aaij, A. S. W. Abdelmotteleb, C. Abellan Beteta, F. Abudinén, T. Ackernley, A. A. Adefisoye, B. Adeva, M. Adinolfi, P. Adlarson, C. Agapopoulou, C. A. Aidala, Z. Ajaltouni, S. Akar, K. Akiba, P. Albicocco, J. Albrecht, F. Alessio, Z. Aliouche, P. Alvarez Cartelle, R. Amalric, S. Amato, J. L. Amey, Y. Amhis, L. An , et al. (1128 additional authors not shown)

Abstract: The transverse polarization of $Λ$ and $\barΛ$ hyperons is measured in $p$Pb collisions collected by the LHCb experiment at a nucleon-nucleon center-of-mass energy of $5.02$ TeV. The polarization is averaged over hyperon transverse momentum in the ranges $0.15 < p_{T} < 6.00 $ GeV/$c$, and Feynman-$x$ in the ranges $0.005 < x_{F} < 0.040$ (forward region) and $-0.10 < x_{F} < -0.01$ (backward regi… ▽ More The transverse polarization of $Λ$ and $\barΛ$ hyperons is measured in $p$Pb collisions collected by the LHCb experiment at a nucleon-nucleon center-of-mass energy of $5.02$ TeV. The polarization is averaged over hyperon transverse momentum in the ranges $0.15 < p_{T} < 6.00 $ GeV/$c$, and Feynman-$x$ in the ranges $0.005 < x_{F} < 0.040$ (forward region) and $-0.10 < x_{F} < -0.01$ (backward region) defined relative to the proton beam direction. The transverse polarization is found to be compatible with zero for both $Λ$ and $\barΛ$ hyperons. The results are also measured as a function of $p_{T}$ and $x_{F}$ with no significant dependence on these variables observed. The results are compared with previous experimental measurements at different center-of-mass energies and collision environments. △ Less

Submitted 5 January, 2026; v1 submitted 3 August, 2025; originally announced August 2025.

Comments: All figures and tables, along with any supplementary material and additional information, are available at https://lbfence.cern.ch/alcm/public/analysis/full-details/3242 (LHCb public pages)

Report number: LHCb-PAPER-2025-004, CERN-EP-2025-153

Journal ref: Phys. Rev. D112 (2025) 112022

Precise Measurement of $^{216}$Po Half-life with Exact Parent-daughter Pairing in PandaX-4T

Authors: PandaX Collaboration, Chenxiang Li, Zihao Bo, Wei Chen, Xun Chen, Yunhua Chen, Chen Cheng, Xiangyi Cui, Manna Deng, Yingjie Fan, Deqing Fang, Xuanye Fu, Zhixing Gao, Yujie Ge, Lisheng Geng, Karl Giboni, Xunan Guo, Xuyuan Guo, Zichao Guo, Chencheng Han, Ke Han, Changda He, Jinrong He, Houqi Huang, Junting Huang , et al. (86 additional authors not shown)

Abstract: We report a precise measurement of $^{216}\rm Po$ half-life using the PandaX-4T liquid xenon time projection chamber (TPC). $^{220}\rm Rn $, emanating from a $^{228}\rm Th $ calibration source, is injected to the detector and undergoes successive $α$ decays, first to $^{216}\rm Po$ and then to $^{212}\rm Pb$. PandaX-4T detector measures the 5-dimensional (5D) information of each decay, including t… ▽ More We report a precise measurement of $^{216}\rm Po$ half-life using the PandaX-4T liquid xenon time projection chamber (TPC). $^{220}\rm Rn $, emanating from a $^{228}\rm Th $ calibration source, is injected to the detector and undergoes successive $α$ decays, first to $^{216}\rm Po$ and then to $^{212}\rm Pb$. PandaX-4T detector measures the 5-dimensional (5D) information of each decay, including time, energy, and 3-dimensional positions. Therefore, we can identify the $^{220}\rm Rn $ and $^{216}\rm Po$ decay events and pair them exactly to extract the lifetime of each $^{216}\rm Po$. With a large data set and high-precision $^{220}\rm $Rn-$^{216}\rm $Po pairing technique, we measure the $^{216}\rm Po$ half-life to be $143.7\pm0.5$ ms, which is the most precise result to date and agrees with previously published values. The leading precision of this measurement demonstrates the power of 5D calorimeter and the potential of exact parent-daughter pairing in the xenon TPC. △ Less

Submitted 17 July, 2025; originally announced July 2025.

Measurement of $ψ(2S)$ to $J/ψ$ cross-section ratio as function of multiplicity in $p$Pb collisions at$\sqrt{s_{NN}} = 8.16$ TeV

Authors: LHCb collaboration, R. Aaij, A. S. W. Abdelmotteleb, C. Abellan Beteta, F. Abudinén, T. Ackernley, A. A. Adefisoye, B. Adeva, M. Adinolfi, P. Adlarson, C. Agapopoulou, C. A. Aidala, Z. Ajaltouni, S. Akar, K. Akiba, P. Albicocco, J. Albrecht, F. Alessio, Z. Aliouche, P. Alvarez Cartelle, R. Amalric, S. Amato, J. L. Amey, Y. Amhis, L. An , et al. (1137 additional authors not shown)

Abstract: The production ratio of $ψ(2S)$ to $J/ψ$ charmonium states is presented as a function of multiplicity in proton-lead collisions at a centre-of-mass energy of $\sqrt{s_{NN}}=8.16$ TeV, for both prompt and nonprompt sources. The total luminosity recorded by the LHCb experiment corresponds to 13.6 $pb^{-1}$ for $p$Pb collisions and 20.8 $pb^{-1}$ for Pb$p$ collisions, where the first particle indicat… ▽ More The production ratio of $ψ(2S)$ to $J/ψ$ charmonium states is presented as a function of multiplicity in proton-lead collisions at a centre-of-mass energy of $\sqrt{s_{NN}}=8.16$ TeV, for both prompt and nonprompt sources. The total luminosity recorded by the LHCb experiment corresponds to 13.6 $pb^{-1}$ for $p$Pb collisions and 20.8 $pb^{-1}$ for Pb$p$ collisions, where the first particle indicates the forward direction of the detector. Measurements are performed in the dimuon final state at forward (backward) centre-of-mass rapidity $1.5<y^*<4.0$ ($-5.0<y^*<-2.5$) for $p$Pb (Pb$p$) collisions.A multiplicity dependence of the prompt production ratio is observed in $p$Pb collisions, whereas no dependence is found in nonprompt production, nor in either prompt or nonprompt production in Pb$p$ collisions. These results suggest that in the Pb-going direction additional suppression mechanisms beyond comover effects may be present, possibly related to the formation of quark-gluon plasma. This highlights a transition from small to large collision systems and provides important insight into the suppression of charmonia in proton-nucleus collisions. △ Less

Submitted 17 February, 2026; v1 submitted 10 June, 2025; originally announced June 2025.

Comments: All figures and tables, along with machine-readable versions and any supplementary material and additional information, are available at https://lbfence.cern.ch/alcm/public/analysis/full-details/4177/ (LHCb public pages)

Report number: LHCb-PAPER-2025-011, CERN-EP-2025-114

Journal ref: JHEP11(2025)169

Coherent photoproduction of $ρ^0, ω$ and excited vector mesons in ultraperipheral PbPb collisions

Authors: LHCb collaboration, R. Aaij, A. S. W. Abdelmotteleb, C. Abellan Beteta, F. Abudinén, T. Ackernley, A. A. Adefisoye, B. Adeva, M. Adinolfi, P. Adlarson, C. Agapopoulou, C. A. Aidala, Z. Ajaltouni, S. Akar, K. Akiba, P. Albicocco, J. Albrecht, F. Alessio, Z. Aliouche, P. Alvarez Cartelle, R. Amalric, S. Amato, J. L. Amey, Y. Amhis, L. An , et al. (1127 additional authors not shown)

Abstract: The invariant-mass distribution for the coherent photoproduction of dipions in ultraperipheral PbPb collisions is measured using data, corresponding to an integrated luminosity of $224.6 \pm 9.6 μ$b$^{-1}$, collected by the LHCb experiment in 2018 at a nucleon-nucleon centre-of-mass energy $\sqrt{s_{\rm NN}}=5.02$ TeV. In the mass range from 400 to 1200 MeV, the results are consistent with previou… ▽ More The invariant-mass distribution for the coherent photoproduction of dipions in ultraperipheral PbPb collisions is measured using data, corresponding to an integrated luminosity of $224.6 \pm 9.6 μ$b$^{-1}$, collected by the LHCb experiment in 2018 at a nucleon-nucleon centre-of-mass energy $\sqrt{s_{\rm NN}}=5.02$ TeV. In the mass range from 400 to 1200 MeV, the results are consistent with previous experiments, with the spectrum dominated by the $ρ^0$ meson, which interferes with a nonresonant component, together with a smaller $ω$ meson contribution. In an extended mass range up to 2300 MeV, models previously used do not fit the data and a consistent description requires the introduction of two resonances at masses of $1350\pm20$ MeV and $1790\pm20$ MeV with widths of about 300 MeV. The cross-section for each meson is measured differentially in twelve bins of rapidity from 2.05 to 4.90. The $ρ^0$ cross-section increases with rapidity from about 400 to 600 mb and is measured with a typical precision of 8\%, while the cross-section times branching fraction for the $ω,ρ^\prime$ and $ρ^{\prime\prime}$, with the statistical precision of the data, do not have a pronounced rapidity dependence and are between 0.5 and 1.5 mb, with uncertainties up to 30\%. A large nuclear suppression is observed for the $ρ^0$ meson compared to expectations based on photoproduction on the proton that use the impulse approximation. Significant suppression is also observed compared to that predicted by elastic scattering described in the Glauber approach, or with the addition of inelastic scattering in a Gribov--Glauber model. △ Less

Submitted 31 December, 2025; v1 submitted 6 June, 2025; originally announced June 2025.

Comments: 31 pages, 7 figures, as published in JHEP 11 (2025) 103. All figures and tables, along with any supplementary material and additional information, are available at https://lbfence.cern.ch/alcm/public/analysis/full-details/3795 (LHCb public pages)

Report number: CERN-EP-2025-106, LHCb-PAPER-2024-042

Journal ref: JHEP 11 (2025) 103

First measurement of $Σ^{+}n\rightarrowΛp$ and $Σ^{+}n\rightarrowΣ^{0}p$ cross sections via $Σ^+$-nucleus scattering at an electron-positron collider

Authors: BESIII Collaboration, M. Ablikim, M. N. Achasov, P. Adlarson, X. C. Ai, R. Aliberti, A. Amoroso, Q. An, Y. Bai, O. Bakina, Y. Ban, H. -R. Bao, V. Batozskaya, K. Begzsuren, N. Berger, M. Berlowski, M. Bertani, D. Bettoni, F. Bianchi, E. Bianco, A. Bortone, I. Boyko, R. A. Briere, A. Brueggemann, H. Cai , et al. (680 additional authors not shown)

Abstract: Using $(1.0087\pm0.0044)\times10^{10}$ $J/ψ$ events collected with the BESIII detector at the BEPCII storage ring, the reactions $Σ^{+}n\rightarrowΛp$ and $Σ^{+}n\rightarrowΣ^{0}p$ are studied, where the $Σ^{+}$ baryon is produced in the process $J/ψ\rightarrowΣ^{+}\barΣ^-$ and the neutron is a component of the $^9\rm{Be}$, $^{12}\rm{C}$ and $^{197}\rm{Au}$ nuclei in the beam pipe. Clear signals o… ▽ More Using $(1.0087\pm0.0044)\times10^{10}$ $J/ψ$ events collected with the BESIII detector at the BEPCII storage ring, the reactions $Σ^{+}n\rightarrowΛp$ and $Σ^{+}n\rightarrowΣ^{0}p$ are studied, where the $Σ^{+}$ baryon is produced in the process $J/ψ\rightarrowΣ^{+}\barΣ^-$ and the neutron is a component of the $^9\rm{Be}$, $^{12}\rm{C}$ and $^{197}\rm{Au}$ nuclei in the beam pipe. Clear signals of these two reactions are observed for the first time. Their cross sections are measured to be $σ(Σ^{+}+{^9\rm{Be}}\rightarrowΛ+p+X)=(45.2\pm12.1_{\rm{stat}}\pm7.2_{\rm{sys}})$ mb and $σ(Σ^{+}+{^9\rm{Be}}\rightarrowΣ^{0}+p+X)=(29.8\pm9.7_{\rm{stat}}\pm6.9_{\rm{sys}})$ mb for a $Σ^{+}$ average momentum of $0.992$ GeV/$c$, within a range of $\pm0.015$ GeV/$c$, where $X$ represents the residual nucleus. This is the first study of $Σ^{+}$-nucleon scattering at an electron-positron collider. △ Less

Submitted 24 March, 2026; v1 submitted 26 May, 2025; originally announced May 2025.

Comments: 9 pages, 2 figures

Journal ref: Physical Review C 113, L032201 (2026)

Rapidity and multiplicity dependence of charged-particle flow in $p$Pb collisions at $\sqrt{s_{NN}} = 8.16$ TeV

Authors: R. Aaij, A. S. W. Abdelmotteleb, C. Abellan Beteta, F. Abudinén, T. Ackernley, A. A. Adefisoye, B. Adeva, M. Adinolfi, P. Adlarson, C. Agapopoulou, C. A. Aidala, Z. Ajaltouni, S. Akar, K. Akiba, P. Albicocco, J. Albrecht, F. Alessio, Z. Aliouche, P. Alvarez Cartelle, R. Amalric, S. Amato, J. L. Amey, Y. Amhis, L. An, L. Anderlini , et al. (1126 additional authors not shown)

Abstract: The elliptic and triangular flow of charged particles are measured using two-particle angular correlations in $p$Pb collisions in the pseudorapidity range \cal{2.0 $< |η| <$ 4.8}. The data sample was collected by the LHCb experiment in 2016 at a centre-of-mass energy per nucleon pair of $\sqrt{s_{NN}} = 8.16$ TeV, containing in total approximately 1.5 billion collision events. Non-flow contributio… ▽ More The elliptic and triangular flow of charged particles are measured using two-particle angular correlations in $p$Pb collisions in the pseudorapidity range \cal{2.0 $< |η| <$ 4.8}. The data sample was collected by the LHCb experiment in 2016 at a centre-of-mass energy per nucleon pair of $\sqrt{s_{NN}} = 8.16$ TeV, containing in total approximately 1.5 billion collision events. Non-flow contributions are obtained in low-multiplicity collisions and subtracted to extract the flow harmonics. The results are presented as a function of event multiplicity and hadron transverse momentum. Comparisons with a full (3+1)D dynamic model indicate that it overestimates the measured elliptic flow. A comparison between the forward and backward regions reveals no significant differences in flow parameters, suggesting that final-state effects may dominate over initial-state effects in the origin of flow in small systems. △ Less

Submitted 30 October, 2025; v1 submitted 14 May, 2025; originally announced May 2025.

Comments: All figures and tables, along with any supplementary material and additional information, are available at https://lbfence.cern.ch/alcm/public/analysis/full-details/3799 (LHCb public pages)

Report number: CERN-EP-2025-090, LHCb-PAPER-2025-003

Journal ref: JHEP 10 (2025) 124

Measurement of the Total Compton Scattering Cross Section between 6.5 and 11 GeV

Authors: GlueX Collaboration, F. Afzal, C. S. Akondi, M. Albrecht, M. Amaryan, S. Arrigo, V. Arroyave, A. Asaturyan, A. Austregesilo, Z. Baldwin, F. Barbosa, J. Barlow, E. Barriga, R. Barsotti, D. Barton, V. Baturin, V. V. Berdnikov, T. Black, W. Boeglin, M. Boer, W. J. Briscoe, T. Britton, R. Brunner, S. Cao, E. Chudakov , et al. (126 additional authors not shown)

Abstract: The total cross section for Compton scattering off atomic electrons, $γ+e\rightarrowγ'+e'$, was measured using photons with energies between 6.5 and 11.1 GeV incident on a $^9$Be target as part of the PrimEx-eta experiment in Hall D at Jefferson Lab. This is the first measurement of this fundamental QED process within this energy range. The total uncertainties of the cross section, combining the s… ▽ More The total cross section for Compton scattering off atomic electrons, $γ+e\rightarrowγ'+e'$, was measured using photons with energies between 6.5 and 11.1 GeV incident on a $^9$Be target as part of the PrimEx-eta experiment in Hall D at Jefferson Lab. This is the first measurement of this fundamental QED process within this energy range. The total uncertainties of the cross section, combining the statistical and systematic components in quadrature, averaged to 3.4% across all energy bins. This not only demonstrates the capability of this experimental setup to perform precision cross-section measurements at forward angles but also allows us to compare with state-of-the-art QED calculations. △ Less

Submitted 30 July, 2025; v1 submitted 12 May, 2025; originally announced May 2025.

Comments: 7 pages, 4 figures, submitted to Physics Letters B

Effective proton-neutron interaction in mirror nuclei

Authors: Y. M. Xing, Y. F. Luo, K. H. Li, Y. H. Zhang, J. G. Li, M. Wang, Yu. A. Litvinov, K. Blaum, X. L. Yan, T. Liao, M. Zhang, X. Zhou

Abstract: Effective proton-neutron interactions, $V_{pn}$, in mirror nuclei are systematically analyzed using the ground-state atomic masses. A mirror symmetry of $V_{pn}$ is found for bound nuclei with a standard deviation of $σ=32$ keV. However, this mirror symmetry is apparently broken for some mirror-nuclei pairs when a proton-unbound nucleus is involved in extracting the $V_{pn}$ values. Such a mirror-… ▽ More Effective proton-neutron interactions, $V_{pn}$, in mirror nuclei are systematically analyzed using the ground-state atomic masses. A mirror symmetry of $V_{pn}$ is found for bound nuclei with a standard deviation of $σ=32$ keV. However, this mirror symmetry is apparently broken for some mirror-nuclei pairs when a proton-unbound nucleus is involved in extracting the $V_{pn}$ values. Such a mirror-symmetry breaking is attributed to the Thomas-Ehrman shift of the proton-unbound nucleus and investigated by using the Gamow shell model. It is concluded that the Thomas-Ehrman shift originates mainly from reduced Coulomb energies in the proton-unbound nuclei due to the extended radial density distribution of valence protons. △ Less

Submitted 3 March, 2025; originally announced March 2025.

$Z=14$ Magicity Revealed by the Mass of the Proton Dripline Nucleus $^{22}$Si

Authors: Y. M. Xing, Y. F. Luo, Y. H. Zhang, M. Wang, X. H. Zhou, J. G. Li, K. H. Li, Q. Yuan, Y. F. Niu, J. Y. Guo, J. C. Pei, F. R. Xu, G. de Angelis, Yu. A. Litvinov, K. Blaum, I. Tanihata, T. Yamaguchi, Y. Yu, X. Zhou, H. S. Xu, Z. Y. Chen, R. J. Chen, H. Y. Deng, C. Y. Fu, W. W. Ge , et al. (14 additional authors not shown)

Abstract: Using the $Bρ$-defined isochronous mass spectrometry technique, we conducted the first mass measurement of the proton dripline nucleus $^{22}$Si. We confirm that $^{22}$Si is bound against particle emission with $S_p/S_{2p}=+1412(114)/+229(54)$ keV, fixing the proton dripline location for the Si element. By analyzing the mass differences of the neighboring $sd$-shell nuclei, we find that $^{22}$Si… ▽ More Using the $Bρ$-defined isochronous mass spectrometry technique, we conducted the first mass measurement of the proton dripline nucleus $^{22}$Si. We confirm that $^{22}$Si is bound against particle emission with $S_p/S_{2p}=+1412(114)/+229(54)$ keV, fixing the proton dripline location for the Si element. By analyzing the mass differences of the neighboring $sd$-shell nuclei, we find that $^{22}$Si exhibits a doubly-magic character similar to its mirror partner $^{22}$O, and that the mirror energy difference of $^{22}$Si-$^{22}$O deviates from the predictions assuming mirror symmetry. Gamow shell-model calculations reveal that the average occupations of valence protons in $^{22}$Si are nearly identical to those of valence neutrons in $^{22}$O, supporting the $Z=14$ magicity in $^{22}$Si. The observed mirror-symmetry breaking is attributed to the extended proton distribution in $^{22}$Si arising from a small contribution of the unbound $\pi2s_{1/2}$ orbital. △ Less

Submitted 3 March, 2025; originally announced March 2025.

Search for Double Beta Decay of $^{136}$Xe to the $0^+_1$ Excited State of $^{136}$Ba with PandaX-4T

Authors: PandaX Collaboration, Lingyin Luo, Zihao Bo, Wei Chen, Xun Chen, Yunhua Chen, Zhaokan Cheng, Xiangyi Cui, Yingji Fang, Deqing Fang, Zhixing Gao, Lisheng Geng, Karl Giboni, Xunan Guo, Xuyuan Guo, Zichao Guo, Chencheng Han, Ke Han, Changda He, Jinrong He, Di Huang, Houqi Huang, Junting Huang, Ruquan Hou, Yu Hou , et al. (76 additional authors not shown)

Abstract: We perform a search of double beta decay of $^{136}$Xe to the excited state, $0^+_1$, of $^{136}$Ba (2$νββ$-0$_1^+$), using the dual-phase xenon detector of PandaX-4T with the first 94.9-day commissioning data. The multi-site events are reconstructed up to the MeV energy scale, which helps to improve the background model significantly. The background contribution from the stainless steel platform… ▽ More We perform a search of double beta decay of $^{136}$Xe to the excited state, $0^+_1$, of $^{136}$Ba (2$νββ$-0$_1^+$), using the dual-phase xenon detector of PandaX-4T with the first 94.9-day commissioning data. The multi-site events are reconstructed up to the MeV energy scale, which helps to improve the background model significantly. The background contribution from the stainless steel platform outside PandaX-4T cryostat is evaluated for the first time. No significant evidence for 2$νββ$-$0_1^+$ is observed, resulting in a lower limit on half-life of $7.5 \times 10^{22}$ yr at the 90% confidence level. This is the first experimental limit on such a rare decay in a natural xenon-based detector. △ Less

Submitted 7 March, 2025; v1 submitted 5 February, 2025; originally announced February 2025.

Measurement of the multiplicity dependence of $\mitΥ$ production ratios in $pp$ collisions at $\sqrt{s}=13$ TeV

Authors: LHCb collaboration, R. Aaij, A. S. W. Abdelmotteleb, C. Abellan Beteta, F. Abudinén, T. Ackernley, A. A. Adefisoye, B. Adeva, M. Adinolfi, P. Adlarson, C. Agapopoulou, C. A. Aidala, Z. Ajaltouni, S. Akar, K. Akiba, P. Albicocco, J. Albrecht, F. Alessio, M. Alexander, Z. Aliouche, P. Alvarez Cartelle, R. Amalric, S. Amato, J. L. Amey, Y. Amhis , et al. (1127 additional authors not shown)

Abstract: The $\mitΥ(\mathrm{2}S)$ and $\mitΥ(\mathrm{3}S)$ production cross-sections are measured relative to that of the $\mitΥ(\mathrm{1}S)$ meson, as a function of charged-particle multiplicity in proton-proton collisions at a centre-of-mass energy of $13$ TeV. The measurement uses data collected by the LHCb experiment in 2018 corresponding to an integrated luminosity of 2 $\text{fb}^{-1}$. Both the… ▽ More The $\mitΥ(\mathrm{2}S)$ and $\mitΥ(\mathrm{3}S)$ production cross-sections are measured relative to that of the $\mitΥ(\mathrm{1}S)$ meson, as a function of charged-particle multiplicity in proton-proton collisions at a centre-of-mass energy of $13$ TeV. The measurement uses data collected by the LHCb experiment in 2018 corresponding to an integrated luminosity of 2 $\text{fb}^{-1}$. Both the $\mitΥ(\mathrm{2}S)$-to-$\mitΥ(\mathrm{1}S)$ and $\mitΥ(\mathrm{3}S)$-to-$\mitΥ(\mathrm{1}S)$ cross-section ratios are found to decrease significantly as a function of event multiplicity, with the $\mitΥ(\mathrm{3}S)$-to-$\mitΥ(\mathrm{1}S)$ ratio showing a steeper decline towards high multiplicity. This hierarchy is qualitatively consistent with the comover model predictions, indicating that final-state interactions play an important role in bottomonia production in high-multiplicity events. △ Less

Submitted 16 May, 2025; v1 submitted 21 January, 2025; originally announced January 2025.

Comments: All figures and tables, along with machine-readable versions and any supplementary material and additional information, are available at https://lbfence.cern.ch/alcm/public/analysis/full-details/1782/ (LHCb public pages)

Report number: LHCb-PAPER-2024-038, CERN-EP-2024-318

Journal ref: JHEP 05 (2025) 011

First Measurement of $a^0_2(1320)$ Polarized Photoproduction Cross Section

Authors: GlueX Collaboration, F. Afzal, C. S. Akondi, M. Albrecht, M. Amaryan, S. Arrigo, V. Arroyave, A. Asaturyan, A. Austregesilo, Z. Baldwin, F. Barbosa, J. Barlow, E. Barriga, R. Barsotti, D. Barton, V. Baturin, V. V. Berdnikov, T. Black, W. Boeglin, M. Boer, W. J. Briscoe, T. Britton, S. Cao, E. Chudakov, G. Chung , et al. (127 additional authors not shown)

Abstract: We measure for the first time the differential photoproduction cross section $dσ/dt$ of the $a_2(1320)$ meson at an average photon beam energy of 8.5~GeV, using data with an integrated luminosity of 104~pb$^{-1}$ collected by the GlueX experiment. We fully reconstruct the $γp \to ηπ^0 p$ reaction and perform a partial-wave analysis in the $a_2(1320)$ mass region with amplitudes that incorporate th… ▽ More We measure for the first time the differential photoproduction cross section $dσ/dt$ of the $a_2(1320)$ meson at an average photon beam energy of 8.5~GeV, using data with an integrated luminosity of 104~pb$^{-1}$ collected by the GlueX experiment. We fully reconstruct the $γp \to ηπ^0 p$ reaction and perform a partial-wave analysis in the $a_2(1320)$ mass region with amplitudes that incorporate the linear polarization of the beam. This allows us to separate for the first time the contributions of natural- and unnatural-parity exchanges. These measurements provide novel information about the photoproduction mechanism, which is critical for the search for spin-exotic states. △ Less

Submitted 6 January, 2025; originally announced January 2025.

Comments: 8 pages, 4 figures plus supplemental material

Searching for Neutrinoless Double-Beta Decay of $^{136}$Xe with PandaX-4T

Authors: PandaX Collaboration, Shu Zhang, Zihao Bo, Wei Chen, Xun Chen, Yunhua Chen, Zhaokan Cheng, Xiangyi Cui, Yingjie Fan, Deqing Fang, Zhixing Gao, Lisheng Geng, Karl Giboni, Xunan Guo, Xuyuan Guo, Zichao Guo, Chencheng Han, Ke Han, Changda He, Jinrong He, Di Huang, Houqi Huang, Junting Huang, Ruquan Hou, Yu Hou , et al. (77 additional authors not shown)

Abstract: We report the search for neutrinoless double-beta decay of $^{136}$Xe from the PandaX-4T experiment with a 3.7-tonne natural xenon target. The data reconstruction and the background modeling are optimized in the MeV energy region. A blind analysis is performed with data from the commissioning run and the first science run. No significant excess of signal over the background is observed. A lower li… ▽ More We report the search for neutrinoless double-beta decay of $^{136}$Xe from the PandaX-4T experiment with a 3.7-tonne natural xenon target. The data reconstruction and the background modeling are optimized in the MeV energy region. A blind analysis is performed with data from the commissioning run and the first science run. No significant excess of signal over the background is observed. A lower limit on the half-life of $^{136}$Xe neutrinoless double-beta decay is established to be $2.1 \times 10^{24}$~yr at the 90\% confidence level, with a $^{136}$Xe exposure of 44.6~kg$\cdot$year. Our result represents the most stringent constraint from a natural xenon detector to date. △ Less

Submitted 18 December, 2024; originally announced December 2024.

Comments: 9 pages, 4 figures, 2 tables

Measurement of two-neutrino double electron capture half-life of $^{124}$Xe with PandaX-4T

Authors: PandaX Collaboration, Zihao Bo, Wei Chen, Xun Chen, Yunhua Chen, Zhaokan Cheng, Xiangyi Cui, Yingjie Fan, Deqing Fang, Zhixing Gao, Lisheng Geng, Karl Giboni, Xunan Guo, Xuyuan Guo, Zichao Guo, Chencheng Han, Ke Han, Changda He, Jinrong He, Di Huang, Houqi Huang, Junting Huang, Ruquan Hou, Yu Hou, Xiangdong Ji , et al. (77 additional authors not shown)

Abstract: Detailed studies of two-neutrino double electron capture (2$ν$DEC) is a crucial step towards searching for the neutrino-less mode to explore the Majorana nature of neutrinos. We have measured precisely the half-life of the 2$ν$DEC process in $^{124}$Xe, utilizing a total exposure of 1.73 tonne$\cdot$year from the commissioning run and the first science run of the PandaX-4T experiment. A time-depen… ▽ More Detailed studies of two-neutrino double electron capture (2$ν$DEC) is a crucial step towards searching for the neutrino-less mode to explore the Majorana nature of neutrinos. We have measured precisely the half-life of the 2$ν$DEC process in $^{124}$Xe, utilizing a total exposure of 1.73 tonne$\cdot$year from the commissioning run and the first science run of the PandaX-4T experiment. A time-dependent background model in the $\mathcal{O}$(10 keV) energy is constructed for the first time in PandaX-4T data. With an unbinned maximum likelihood fit, we determine the half-life of the 2$ν$DEC process to be $(1.03\pm0.15_{\rm stat}\pm0.08_{\rm sys})\times 10^{22}$$\,$yr. Furthermore, we have evaluated the branching ratio for both electrons captured from the $K$ shell ($KK$) to be $(65\pm5)\%$, which aligns with the $^{124}$Xe nuclear model calculations within 1.8$\,$$σ$. △ Less

Submitted 16 May, 2025; v1 submitted 21 November, 2024; originally announced November 2024.

Comments: 19 pages, 5 figures, 4 tables; version3 accepted by JHEP

Measurement of $φ(1020)$ meson production in fixed-target $\textit{p}$Ne collisions at $\sqrt{s_{NN}}$ = 68.5 GeV

Authors: LHCb collaboration, R. Aaij, A. S. W. Abdelmotteleb, C. Abellan Beteta, F. Abudinén, T. Ackernley, A. A. Adefisoye, B. Adeva, M. Adinolfi, P. Adlarson, C. Agapopoulou, C. A. Aidala, Z. Ajaltouni, S. Akar, K. Akiba, P. Albicocco, J. Albrecht, F. Alessio, M. Alexander, Z. Aliouche, P. Alvarez Cartelle, R. Amalric, S. Amato, J. L. Amey, Y. Amhis , et al. (1127 additional authors not shown)

Abstract: The first measurement of $φ(1020)$ meson production in fixed-target $p$Ne collisions at $\sqrt{s_{NN}}=68.5$ GeV is presented. The $φ(1020)$ mesons are reconstructed in their $K^{+}K^{-}$ decay in a data sample consisting of proton collisions on neon nuclei at rest, corresponding to an integrated luminosity of $21.7 \pm 1.4$ nb$^{-1}$, collected by the LHCb detector at CERN. The $φ(1020)$ producti… ▽ More The first measurement of $φ(1020)$ meson production in fixed-target $p$Ne collisions at $\sqrt{s_{NN}}=68.5$ GeV is presented. The $φ(1020)$ mesons are reconstructed in their $K^{+}K^{-}$ decay in a data sample consisting of proton collisions on neon nuclei at rest, corresponding to an integrated luminosity of $21.7 \pm 1.4$ nb$^{-1}$, collected by the LHCb detector at CERN. The $φ(1020)$ production cross-section in the centre-of-mass rapidity range of $-1.8<y^*<0$ and transverse momentum range of $800<p_{T}<6500$ MeV/c is found to be $σ=182.7\pm2.7~\text{(stat.)}\pm14.1~\text{(syst)}~μ$b/nucleon. A double-differential measurement of the cross-section is also provided in four regions of rapidity and six regions of transverse momentum of the $φ(1020)$ meson and compared with the predictions from Pythia and EPOS4, which are found to underestimate the experimental values. △ Less

Submitted 24 March, 2025; v1 submitted 14 November, 2024; originally announced November 2024.

Comments: All figures and tables, along with machine-readable versions and any supplementary material and additional information, are available at https://lbfence.cern.ch/alcm/public/analysis/full-details/3673 (LHCb public pages)

Report number: LHCb-PAPER-2024-036, CERN-EP-2024-274

Journal ref: JHEP 03 (2025) 151

Measurement of the $ψ(2S)$ to $J/ψ$ cross-section ratio as a function of centrality in PbPb collisions at $\sqrt{s_{\text{NN}}}$ = 5.02 TeV

Authors: LHCb collaboration, R. Aaij, A. S. W. Abdelmotteleb, C. Abellan Beteta, F. Abudinén, T. Ackernley, A. A. Adefisoye, B. Adeva, M. Adinolfi, P. Adlarson, C. Agapopoulou, C. A. Aidala, Z. Ajaltouni, S. Akar, K. Akiba, P. Albicocco, J. Albrecht, F. Alessio, M. Alexander, Z. Aliouche, P. Alvarez Cartelle, R. Amalric, S. Amato, J. L. Amey, Y. Amhis , et al. (1128 additional authors not shown)

Abstract: The dissociation of quarkonium states with different binding energies produced in heavy-ion collisions is a powerful probe for investigating the formation and properties of the quark-gluon plasma. The ratio of production cross-sections of $ψ(2S)$ and $J/ψ$ mesons times the ratio of their branching fractions into the dimuon final state is measured as a function of centrality using data collected by… ▽ More The dissociation of quarkonium states with different binding energies produced in heavy-ion collisions is a powerful probe for investigating the formation and properties of the quark-gluon plasma. The ratio of production cross-sections of $ψ(2S)$ and $J/ψ$ mesons times the ratio of their branching fractions into the dimuon final state is measured as a function of centrality using data collected by the LHCb detector in PbPb collisions at $\sqrt{s_{\text{NN}}}$ = 5.02 TeV. The measured ratio shows no dependence on the collision centrality, and is compared to the latest theory predictions and to the recent measurements in literature. △ Less

Submitted 13 November, 2025; v1 submitted 8 November, 2024; originally announced November 2024.

Comments: All figures and tables, along with any supplementary material and additional information, are available at https://lbfence.cern.ch/alcm/public/analysis/full-details/3695 (LHCb public pages)

Report number: CERN-EP-2024-272, LHCb-PAPER-2024-041

Journal ref: JHEP07(2025)235

Nuclear structure of dripline nuclei elucidated through precision mass measurements of $^{23}$Si, $^{26}$P, $^{27,28}$S, and $^{31}$Ar

Authors: Y. Yu, Y. M. Xing, Y. H. Zhang, M. Wang, X. H. Zhou, J. G. Li, H. H. Li, Q. Yuan, Y. F. Niu, Y. N. Huang, J. Geng, J. Y. Guo, J. W. Chen, J. C. Pei, F. R. Xu, Yu. A. Litvinov, K. Blaum, G. de Angelis, I. Tanihata, T. Yamaguchi, X. Zhou, H. S. Xu, Z. Y. Chen, R. J. Chen, H. Y. Deng , et al. (17 additional authors not shown)

Abstract: Using the B$ρ$-defined isochronous mass spectrometry technique, we report the first determination of the $^{23}$Si, $^{26}$P, $^{27}$S, and $^{31}$Ar masses and improve the precision of the $^{28}$S mass by a factor of 11. Our measurements confirm that these isotopes are bound and fix the location of the proton dripline in P, S, and Ar. We find that the mirror energy differences of the mirror-nucl… ▽ More Using the B$ρ$-defined isochronous mass spectrometry technique, we report the first determination of the $^{23}$Si, $^{26}$P, $^{27}$S, and $^{31}$Ar masses and improve the precision of the $^{28}$S mass by a factor of 11. Our measurements confirm that these isotopes are bound and fix the location of the proton dripline in P, S, and Ar. We find that the mirror energy differences of the mirror-nuclei pairs $^{26}$P-$^{26}$Na, $^{27}$P-$^{27}$Mg, $^{27}$S-$^{27}$Na, $^{28}$S-$^{28}$Mg, and $^{31}$Ar-$^{31}$Al deviate significantly from the values predicted assuming mirror symmetry. In addition, we observe similar anomalies in the excited states, but not in the ground states, of the mirror-nuclei pairs $^{22}$Al-$^{22}$F and $^{23}$Al-$^{23}$Ne. Using $ab~ initio$ VS-IMSRG and mean field calculations, we show that such a mirror-symmetry breaking phenomeon can be explained by the extended charge distributions of weakly-bound, proton-rich nuclei. When observed, this phenomenon serves as a unique signature that can be valuable for identifying proton-halo candidates. △ Less

Submitted 23 October, 2024; originally announced October 2024.

Observation of a rare beta decay of the charmed baryon with a Graph Neural Network

Authors: BESIII Collaboration, M. Ablikim, M. N. Achasov, P. Adlarson, O. Afedulidis, X. C. Ai, R. Aliberti, A. Amoroso, Q. An, Y. Bai, O. Bakina, I. Balossino, Y. Ban, H. -R. Bao, V. Batozskaya, K. Begzsuren, N. Berger, M. Berlowski, M. Bertani, D. Bettoni, F. Bianchi, E. Bianco, A. Bortone, I. Boyko, R. A. Briere , et al. (637 additional authors not shown)

Abstract: The beta decay of the lightest charmed baryon $Λ_c^+$ provides unique insights into the fundamental mechanism of strong and electro-weak interactions, serving as a testbed for investigating non-perturbative quantum chromodynamics and constraining the Cabibbo-Kobayashi-Maskawa (CKM) matrix parameters. This article presents the first observation of the Cabibbo-suppressed decay… ▽ More The beta decay of the lightest charmed baryon $Λ_c^+$ provides unique insights into the fundamental mechanism of strong and electro-weak interactions, serving as a testbed for investigating non-perturbative quantum chromodynamics and constraining the Cabibbo-Kobayashi-Maskawa (CKM) matrix parameters. This article presents the first observation of the Cabibbo-suppressed decay $Λ_c^+ \rightarrow n e^+ ν_{e}$, utilizing $4.5~\mathrm{fb}^{-1}$ of electron-positron annihilation data collected with the BESIII detector. A novel Graph Neural Network based technique effectively separates signals from dominant backgrounds, notably $Λ_c^+ \rightarrow Λe^+ ν_{e}$, achieving a statistical significance exceeding $10σ$. The absolute branching fraction is measured to be $(3.57\pm0.34_{\mathrm{stat.}}\pm0.14_{\mathrm{syst.}})\times 10^{-3}$. For the first time, the CKM matrix element $\left|V_{cd}\right|$ is extracted via a charmed baryon decay as $0.208\pm0.011_{\rm exp.}\pm0.007_{\rm LQCD}\pm0.001_{τ_{Λ_c^+}}$. This work highlights a new approach to further understand fundamental interactions in the charmed baryon sector, and showcases the power of modern machine learning techniques in experimental high-energy physics. △ Less

Submitted 15 January, 2025; v1 submitted 17 October, 2024; originally announced October 2024.

Comments: 27 pages, 5 figures

Journal ref: Nature Commun. 16, 681 (2025)

First Measurement of Near- and Sub-Threshold $J/ψ$ Photoproduction off Nuclei

Authors: J. R. Pybus, L. Ehinger, T. Kolar, B. Devkota, P. Sharp, B. Yu, M. M. Dalton, D. Dutta, H. Gao, O. Hen, E. Piasetzky, S. N. Santiesteban, A. Schmidt, A. Somov, H. Szumila-Vance, S. Adhikari, A. Asaturyan, A. Austregesilo, C. Ayerbe Gayoso, J. Barlow, V. V. Berdnikov, H. D. Bhatt, Deepak Bhetuwal, T. Black, W. J. Briscoe , et al. (43 additional authors not shown)

Abstract: We report on the first measurement of $J/ψ$ photoproduction from nuclei in the photon energy range of $7$ to $10.8$ GeV, extending above and below the photoproduction threshold in the free proton of $\sim8.2$ GeV. The experiment used a tagged photon beam incident on deuterium, helium, and carbon, and the GlueX detector at Jefferson Lab to measure the semi-inclusive $A(γ,e^+e^-p)$ reaction with a d… ▽ More We report on the first measurement of $J/ψ$ photoproduction from nuclei in the photon energy range of $7$ to $10.8$ GeV, extending above and below the photoproduction threshold in the free proton of $\sim8.2$ GeV. The experiment used a tagged photon beam incident on deuterium, helium, and carbon, and the GlueX detector at Jefferson Lab to measure the semi-inclusive $A(γ,e^+e^-p)$ reaction with a dilepton invariant mass $M(e^+e^-)\sim m_{J/ψ}=3.1$ GeV. The incoherent $J/ψ$ photoproduction cross sections in the measured nuclei are extracted as a function of the incident photon energy, momentum transfer, and proton reconstructed missing light-cone momentum fraction. Comparisons with theoretical predictions assuming a dipole form factor allow extracting a gluonic radius for bound protons of $\sqrt{\langle r^2\rangle}=0.85\pm0.14$ fm. The data also suggest an excess of the measured cross section for sub-threshold production and for interactions with high missing light-cone momentum fraction protons. The measured enhancement can be explained by modified gluon structure for high-virtuality bound-protons. △ Less

Submitted 23 October, 2024; v1 submitted 27 September, 2024; originally announced September 2024.

First Indication of Solar $^8$B Neutrino Flux through Coherent Elastic Neutrino-Nucleus Scattering in PandaX-4T

Authors: PandaX Collaboration, Zihao Bo, Wei Chen, Xun Chen, Yunhua Chen, Zhaokan Cheng, Xiangyi Cui, Yingjie Fan, Deqing Fang, Zhixing Gao, Lisheng Geng, Karl Giboni, Xunan Guo, Xuyuan Guo, Zichao Guo, Chencheng Han, Ke Han, Changda He, Jinrong He, Di Huang, Houqi Huang, Junting Huang, Ruquan Hou, Yu Hou, Xiangdong Ji , et al. (77 additional authors not shown)

Abstract: The PandaX-4T liquid xenon detector at the China Jinping Underground Laboratory is used to measure the solar $^8$B neutrino flux by detecting neutrinos through coherent scattering with xenon nuclei. Data samples requiring the coincidence of scintillation and ionization signals (paired), as well as unpaired ionization-only signals (US2), are selected with energy threshold of approximately 1.1 keV (… ▽ More The PandaX-4T liquid xenon detector at the China Jinping Underground Laboratory is used to measure the solar $^8$B neutrino flux by detecting neutrinos through coherent scattering with xenon nuclei. Data samples requiring the coincidence of scintillation and ionization signals (paired), as well as unpaired ionization-only signals (US2), are selected with energy threshold of approximately 1.1 keV (0.33 keV) nuclear recoil energy. Combining the commissioning run and the first science run of PandaX-4T, a total exposure of 1.20 and 1.04 tonne$\cdot$year are collected for the paired and US2, respectively. After unblinding, 3 and 332 events are observed with an expectation of 2.8$\pm$0.5 and 251$\pm$32 background events, for the paired and US2 data, respectively. A combined analysis yields a best-fit $^8$B neutrino signal of 3.5 (75) events from the paired (US2) data sample, with $\sim$37\% uncertainty, and the background-only hypothesis is disfavored at 2.64$σ$ significance. This gives a solar $^8$B neutrino flux of ($8.4\pm3.1$)$\times$10$^6$ cm$^{-2}$s$^{-1}$, consistent with the standard solar model prediction. It is also the first indication of solar $^8$B neutrino ``fog'' in a dark matter direct detection experiment. △ Less

Submitted 13 September, 2024; v1 submitted 15 July, 2024; originally announced July 2024.

Comments: Accepted by Physical Review Letters

Upper Limit on the Photoproduction Cross Section of the Spin-Exotic $π_1(1600)$

Authors: GlueX Collaboration, F. Afzal, C. S. Akondi, M. Albrecht, M. Amaryan, S. Arrigo, V. Arroyave, A. Asaturyan, A. Austregesilo, Z. Baldwin, F. Barbosa, J. Barlow, E. Barriga, R. Barsotti, D. Barton, V. Baturin, V. V. Berdnikov, T. Black, W. Boeglin, M. Boer, W. J. Briscoe, T. Britton, S. Cao, E. Chudakov, G. Chung , et al. (125 additional authors not shown)

Abstract: The spin-exotic hybrid meson $π_{1}(1600)$ is predicted to have a large decay rate to the $ωππ$ final state. Using 76.6~pb$^{-1}$ of data collected with the GlueX detector, we measure the cross sections for the reactions $γp \to ωπ^+ π^- p$, $γp \to ωπ^0 π^0 p$, and $γp\toωπ^-π^0Δ^{++}$ in the range $E_γ=$ 8-10 GeV. Using isospin conservation, we set the first upper limits on the photoproduction c… ▽ More The spin-exotic hybrid meson $π_{1}(1600)$ is predicted to have a large decay rate to the $ωππ$ final state. Using 76.6~pb$^{-1}$ of data collected with the GlueX detector, we measure the cross sections for the reactions $γp \to ωπ^+ π^- p$, $γp \to ωπ^0 π^0 p$, and $γp\toωπ^-π^0Δ^{++}$ in the range $E_γ=$ 8-10 GeV. Using isospin conservation, we set the first upper limits on the photoproduction cross sections of the $π^{0}_{1}(1600)$ and $π^{-}_{1}(1600)$. We combine these limits with lattice calculations of decay widths and find that photoproduction of $η'π$ is the most sensitive two-body system to search for the $π_1(1600)$. △ Less

Submitted 9 January, 2025; v1 submitted 3 July, 2024; originally announced July 2024.

Comments: 7 pages, 3 figures plus supplemental materials

Journal ref: Phys.Rev.Lett. 133 (2024) 26, 261903

Measurement of Spin-Density Matrix Elements in $Δ^{++}(1232)$ photoproduction

Authors: F. Afzal, C. S. Akondi, M. Albrecht, M. Amaryan, S. Arrigo, V. Arroyave, A. Asaturyan, A. Austregesilo, Z. Baldwin, F. Barbosa, J. Barlow, E. Barriga, R. Barsotti, D. Barton, V. Baturin, V. V. Berdnikov, T. Black, W. Boeglin, M. Boer, W. J. Briscoe, T. Britton, S. Cao, E. Chudakov, G. Chung, P. L. Cole , et al. (124 additional authors not shown)

Abstract: We measure the spin-density matrix elements (SDMEs) of the $Δ^{++}(1232)$ in the photoproduction reaction $γp \to π^-Δ^{++}(1232)$ with the GlueX experiment in Hall D at Jefferson Lab. The measurement uses a linearly--polarized photon beam with energies from $8.2$ to $8.8$~GeV and the statistical precision of the SDMEs exceeds the previous measurement by three orders of magnitude for the momentum… ▽ More We measure the spin-density matrix elements (SDMEs) of the $Δ^{++}(1232)$ in the photoproduction reaction $γp \to π^-Δ^{++}(1232)$ with the GlueX experiment in Hall D at Jefferson Lab. The measurement uses a linearly--polarized photon beam with energies from $8.2$ to $8.8$~GeV and the statistical precision of the SDMEs exceeds the previous measurement by three orders of magnitude for the momentum transfer squared region below $1.4$ GeV$^2$. The data are sensitive to the previously undetermined relative sign between couplings in existing Regge-exchange models. Linear combinations of the extracted SDMEs allow for a decomposition into natural and unnatural--exchange amplitudes. We find that the unnatural exchange plays an important role in the low momentum transfer region. △ Less

Submitted 26 July, 2024; v1 submitted 18 June, 2024; originally announced June 2024.

Neutron radius determination of 133Cs and its impact on the interpretation of CEvNS-CsI measurement

Authors: Y. Huang, S. Y. Xia, Y. F. Li, X. L. Tu, J. T. Zhang, C. J. Shao, K. Yue, P. Ma, Y. F. Niu, Z. P. Li, Y. Kuang, X. Q. Liu, J. F. Han, P. Egelhof, Yu. A. Litvinov, M. Wang, Y. H. Zhang, X. H. Zhou, Z. Y. Sun

Abstract: Proton-$^{133}$Cs elastic scattering at low momentum transfer is performed using an in-ring reaction technique at the Cooler Storage Ring at the Heavy Ion Research Facility in Lanzhou. Recoil protons from the elastic collisions between the internal H$_2$-gas target and the circulating $^{133}$Cs ions at 199.4 MeV/u are detected by a silicon-strip detector. The matter radius of $^{133}$Cs is deduce… ▽ More Proton-$^{133}$Cs elastic scattering at low momentum transfer is performed using an in-ring reaction technique at the Cooler Storage Ring at the Heavy Ion Research Facility in Lanzhou. Recoil protons from the elastic collisions between the internal H$_2$-gas target and the circulating $^{133}$Cs ions at 199.4 MeV/u are detected by a silicon-strip detector. The matter radius of $^{133}$Cs is deduced by describing the measured differential cross sections using the Glauber model. Employing the adopted proton distribution radius, a point-neutron radius of 4.86(21) fm for $^{133}$Cs is obtained. With the newly determined neutron radius, the weak mixing angle sin$^2 θ_W$ is independently extracted to be 0.227(28) by fitting the coherent elastic neutrino-nucleus scattering data. Our work limits the sin$^2 θ_W$ value in a range smaller than the ones proposed by the previous independent approaches, and would play an important role in searching new physics via the high precision CE$ν$NS-CsI cross section data in the near future. △ Less

Submitted 8 April, 2024; v1 submitted 6 March, 2024; originally announced March 2024.

Modification of $χ_{c1}$(3872) and $ψ$(2$S$) production in $p$Pb collisions at $\sqrt{s_{NN}} = 8.16$ TeV

Authors: LHCb collaboration, R. Aaij, A. S. W. Abdelmotteleb, C. Abellan Beteta, F. Abudinén, T. Ackernley, B. Adeva, M. Adinolfi, P. Adlarson, C. Agapopoulou, C. A. Aidala, Z. Ajaltouni, S. Akar, K. Akiba, P. Albicocco, J. Albrecht, F. Alessio, M. Alexander, A. Alfonso Albero, Z. Aliouche, P. Alvarez Cartelle, R. Amalric, S. Amato, J. L. Amey, Y. Amhis , et al. (1082 additional authors not shown)

Abstract: The LHCb collaboration measures production of the exotic hadron $χ_{c1}$(3872) in proton-nucleus collisions for the first time. Comparison with the charmonium state $ψ$(2$S$) suggests that the exotic $χ_{c1}$(3872) experiences different dynamics in the nuclear medium than conventional hadrons, and comparison with data from proton-proton collisions indicates that the presence of the nucleus may mod… ▽ More The LHCb collaboration measures production of the exotic hadron $χ_{c1}$(3872) in proton-nucleus collisions for the first time. Comparison with the charmonium state $ψ$(2$S$) suggests that the exotic $χ_{c1}$(3872) experiences different dynamics in the nuclear medium than conventional hadrons, and comparison with data from proton-proton collisions indicates that the presence of the nucleus may modify $χ_{c1}$(3872) production rates. This is the first measurement of the nuclear modification factor of an exotic hadron. △ Less

Submitted 19 June, 2024; v1 submitted 22 February, 2024; originally announced February 2024.

Comments: All figures and tables, along with any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2023-026.html (LHCb public pages)

Report number: LHCb-PAPER-2023-026, CERN-EP-2024-033

Journal ref: Phys. Rev. Lett. 132 (2024) 242301

Ground-state mass of $^{22}$Al and test of state-of-the-art \textit{ab initio} calculations

Authors: M. Z. Sun, Y. Yu, X. P. Wang, M. Wang, J. G. Li, Y. H. Zhang, K. Blaum, Z. Y. Chen, R. J. Chen, H. Y. Deng, C. Y. Fu, W. W. Ge, W. J. Huang, H. Y. Jiao, H. H. Li, H. F. Li, Y. F. Luo, T. Liao, Yu. A. Litvinov, M. Si, P. Shuai, J. Y. Shi, Q. Wang, Y. M. Xing, X. Xu , et al. (11 additional authors not shown)

Abstract: The ground-state mass excess of the $T_{z}=-2$ drip-line nucleus $^{22}$Al is measured for the first time to be $18103(10)$ keV using the newly-developed B$ρ$-defined isochronous mass spectrometry method at the cooler storage ring in Lanzhou. The new mass excess value allowed us to determine the excitation energies of the two low-lying $1^+$ states in $^{22}$Al with significantly reduced uncertain… ▽ More The ground-state mass excess of the $T_{z}=-2$ drip-line nucleus $^{22}$Al is measured for the first time to be $18103(10)$ keV using the newly-developed B$ρ$-defined isochronous mass spectrometry method at the cooler storage ring in Lanzhou. The new mass excess value allowed us to determine the excitation energies of the two low-lying $1^+$ states in $^{22}$Al with significantly reduced uncertainties of 51 keV. Comparing to the analogue states in its mirror nucleus $^{22}$F, the mirror energy differences of the two $1^+$ states in the $^{22}$Al-$^{22}$F mirror pair are determined to be $-625(51)$ keV and $-330(51)$ keV, respectively. The excitation energies and the mirror energy differences are used to test the state-of-the-art \textit{ab initio} valence-space in-medium similarity renormalization group calculations with four sets of interactions derived from the chiral effective field theory. The mechanism leading to the large mirror energy differences is investigated and attributed to the occupation of the $πs_{1/2}$ orbital. △ Less

Submitted 26 January, 2024; originally announced January 2024.

Comments: 8 pages, 5 figures

Prompt and nonprompt $ψ(2S)$ production in $p$Pb collisions at $\sqrt{s_{NN}}=8.16$ TeV

Authors: LHCb collaboration, R. Aaij, A. S. W. Abdelmotteleb, C. Abellan Beteta, F. Abudinén, T. Ackernley, B. Adeva, M. Adinolfi, P. Adlarson, H. Afsharnia, C. Agapopoulou, C. A. Aidala, Z. Ajaltouni, S. Akar, K. Akiba, P. Albicocco, J. Albrecht, F. Alessio, M. Alexander, A. Alfonso Albero, Z. Aliouche, P. Alvarez Cartelle, R. Amalric, S. Amato, J. L. Amey , et al. (1079 additional authors not shown)

Abstract: The production of $ψ(2S)$ mesons in proton-lead collisions at a centre-of-mass energy per nucleon pair of $\sqrt{s_{NN}}=8.16$ TeV is studied with the LHCb detector using data corresponding to an integrated luminosity of 34 nb$^{-1}$. The prompt and nonprompt $ψ(2S)$ production cross-sections and the ratio of the $ψ(2S)$ to $J/ψ$ cross-section are measured as a function of the meson transverse mom… ▽ More The production of $ψ(2S)$ mesons in proton-lead collisions at a centre-of-mass energy per nucleon pair of $\sqrt{s_{NN}}=8.16$ TeV is studied with the LHCb detector using data corresponding to an integrated luminosity of 34 nb$^{-1}$. The prompt and nonprompt $ψ(2S)$ production cross-sections and the ratio of the $ψ(2S)$ to $J/ψ$ cross-section are measured as a function of the meson transverse momentum and rapidity in the nucleon-nucleon centre-of-mass frame, together with forward-to-backward ratios and nuclear modification factors. The production of prompt $ψ(2S)$ is observed to be more suppressed compared to $pp$ collisions than the prompt $J/ψ$ production, while the nonprompt productions have similar suppression factors. △ Less

Submitted 22 April, 2024; v1 submitted 20 January, 2024; originally announced January 2024.

Comments: All figures and tables, along with machine-readable versions and any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2023-024.html (LHCb public pages)

Report number: LHCb-PAPER-2023-024, CERN-EP-2023-293

Journal ref: JHEP 04 (2024) 111

First study of antihyperon-nucleon scattering $\barΛp\rightarrow\barΛp$ and measurement of $Λp\rightarrowΛp$ cross section

Authors: BESIII Collaboration, M. Ablikim, M. N. Achasov, P. Adlarson, O. Afedulidis, X. C. Ai, R. Aliberti, A. Amoroso, Q. An, Y. Bai, O. Bakina, I. Balossino, Y. Ban, H. -R. Bao, V. Batozskaya, K. Begzsuren, N. Berger, M. Berlowski, M. Bertani, D. Bettoni, F. Bianchi, E. Bianco, A. Bortone, I. Boyko, R. A. Briere , et al. (634 additional authors not shown)

Abstract: Using $(10.087\pm0.044)\times10^{9}$ $J/ψ$ events collected with the BESIII detector at the BEPCII storage ring, the processes $Λp\rightarrowΛp$ and $\barΛp\rightarrow\barΛp$ are studied, where the $Λ/\barΛ$ baryons are produced in the process $J/ψ\rightarrowΛ\barΛ$ and the protons are the hydrogen nuclei in the cooling oil of the beam pipe. Clear signals are observed for the two reactions. The cr… ▽ More Using $(10.087\pm0.044)\times10^{9}$ $J/ψ$ events collected with the BESIII detector at the BEPCII storage ring, the processes $Λp\rightarrowΛp$ and $\barΛp\rightarrow\barΛp$ are studied, where the $Λ/\barΛ$ baryons are produced in the process $J/ψ\rightarrowΛ\barΛ$ and the protons are the hydrogen nuclei in the cooling oil of the beam pipe. Clear signals are observed for the two reactions. The cross sections in $-0.9\leq\rm{cos}θ_{Λ/\barΛ}\leq0.9$ are measured to be $σ(Λp\rightarrowΛp)=(12.2\pm1.6_{\rm{stat}}\pm1.1_{\rm{sys}})$ mb and $σ(\barΛ p\rightarrow\barΛ p)=(17.5\pm2.1_{\rm{stat}}\pm1.6_{\rm{sys}})$ mb at the $Λ/\barΛ$ momentum of $1.074$ GeV/$c$ within a range of $\pm0.017$ GeV/$c$, where the $θ_{Λ/\barΛ}$ are the scattering angles of the $Λ/\barΛ$ in the $Λp/\barΛp$ rest frames. Furthermore, the differential cross sections of the two reactions are also measured, where there is a slight tendency of forward scattering for $Λp\rightarrowΛp$, and a strong forward peak for $\barΛp\rightarrow\barΛp$. We present an approach to extract the total elastic cross sections by extrapolation. The study of $\barΛp\rightarrow\barΛp$ represents the first study of antihyperon-nucleon scattering, and these new measurements will serve as important inputs for the theoretical understanding of the (anti)hyperon-nucleon interaction. △ Less

Submitted 18 May, 2024; v1 submitted 17 January, 2024; originally announced January 2024.

Comments: 9 pages, 5 figures

Searching for Two-Neutrino and Neutrinoless Double Beta Decay of $^{134}$Xe with the PandaX-4T Experiment

Authors: PandaX Collaboration, Xiyu Yan, Zhaokan Cheng, Abdusalam Abdukerim, Zihao Bo, Wei Chen, Xun Chen, Chen Cheng, Xiangyi Cui, Yingjie Fan, Deqing Fang, Changbo Fu, Mengting Fu, Lisheng Geng, Karl Giboni, Linhui Gu, Xuyuan Guo, Chencheng Han, Ke Han, Changda He, Jinrong He, Di Huang, Yanlin Huang, Junting Huang, Zhou Huang , et al. (72 additional authors not shown)

Abstract: $^{134}$Xe is a candidate isotope for neutrinoless double beta decay~($0νββ$) search. In addition, the two-neutrino case ($2νββ$) allowed by the Standard Model of particle physics has not yet been observed. Utilizing the 10.4% of $^{134}$Xe in the natural xenon in the PandaX-4T detector and its first 94.9-day exposure, we have established the most stringent constraints on $2νββ$ and $0νββ$ of $^{1… ▽ More $^{134}$Xe is a candidate isotope for neutrinoless double beta decay~($0νββ$) search. In addition, the two-neutrino case ($2νββ$) allowed by the Standard Model of particle physics has not yet been observed. Utilizing the 10.4% of $^{134}$Xe in the natural xenon in the PandaX-4T detector and its first 94.9-day exposure, we have established the most stringent constraints on $2νββ$ and $0νββ$ of $^{134}$Xe half-lives, with limits of $2.8\times10^{22}$ yr and $3.0\times10^{23}$ yr at 90% confidence level, respectively. The $2νββ$ ($0νββ$) limit surpasses the previously reported best result by a factor of 32 (2.7), highlighting the potential of large monolithic natural xenon detectors. △ Less

Submitted 28 April, 2024; v1 submitted 25 December, 2023; originally announced December 2023.

Journal ref: Phys.Rev.Lett. 132 (2024) 15, 152502

Measurement of forward charged hadron flow harmonics in peripheral PbPb collisions at $\sqrt{s_{NN}}=5.02$ TeV with the LHCb detector

Authors: LHCb collaboration, R. Aaij, A. S. W. Abdelmotteleb, C. Abellan Beteta, F. Abudinén, T. Ackernley, B. Adeva, M. Adinolfi, P. Adlarson, C. Agapopoulou, C. A. Aidala, Z. Ajaltouni, S. Akar, K. Akiba, P. Albicocco, J. Albrecht, F. Alessio, M. Alexander, A. Alfonso Albero, Z. Aliouche, P. Alvarez Cartelle, R. Amalric, S. Amato, J. L. Amey, Y. Amhis , et al. (1079 additional authors not shown)

Abstract: Flow harmonic coefficients, $v_n$, which are the key to studying the hydrodynamics of the quark-gluon plasma (QGP) created in heavy-ion collisions, have been measured in various collision systems and kinematic regions and using various particle species. The study of flow harmonics in a wide pseudorapidity range is particularly valuable to understand the temperature dependence of the shear viscosit… ▽ More Flow harmonic coefficients, $v_n$, which are the key to studying the hydrodynamics of the quark-gluon plasma (QGP) created in heavy-ion collisions, have been measured in various collision systems and kinematic regions and using various particle species. The study of flow harmonics in a wide pseudorapidity range is particularly valuable to understand the temperature dependence of the shear viscosity to entropy density ratio of the QGP. This paper presents the first LHCb results of the second- and the third-order flow harmonic coefficients of charged hadrons as a function of transverse momentum in the forward region, corresponding to pseudorapidities between 2.0 and 4.9, using the data collected from PbPb collisions in 2018 at a center-of-mass energy of $5.02$ TeV. The coefficients measured using the two-particle angular correlation analysis method are smaller than the central-pseudorapidity measurements at ALICE and ATLAS from the same collision system but share similar features. △ Less

Submitted 16 May, 2024; v1 submitted 16 November, 2023; originally announced November 2023.

Comments: All figures and tables, along with any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2023-031.html (LHCb public pages)

Report number: LHCb-PAPER-2023-031, CERN-EP-2023-240

Journal ref: Phys. Rev. C 109 (2024) 054908

Observation of strangeness enhancement with charmed mesons in high-multiplicity $p\mathrm{Pb}$ collisions at $\sqrt {s_{\mathrm{NN}}}=8.16\,$TeV

Authors: LHCb collaboration, R. Aaij, A. S. W. Abdelmotteleb, C. Abellan Beteta, F. Abudinén, T. Ackernley, B. Adeva, M. Adinolfi, P. Adlarson, H. Afsharnia, C. Agapopoulou, C. A. Aidala, Z. Ajaltouni, S. Akar, K. Akiba, P. Albicocco, J. Albrecht, F. Alessio, M. Alexander, A. Alfonso Albero, Z. Aliouche, P. Alvarez Cartelle, R. Amalric, S. Amato, J. L. Amey , et al. (1085 additional authors not shown)

Abstract: The production of prompt $D^+_{s}$ and $D^+$ mesons is measured by the LHCb experiment in proton-lead ($p\mathrm{Pb}$) collisions in both the forward ($1.5<y^*<4.0$) and backward ($-5.0<y^*<-2.5$) rapidity regions at a nucleon-nucleon center-of-mass energy of $\sqrt {s_{\mathrm{NN}}}=8.16\,$TeV. The nuclear modification factors of both $D^+_{s}$ and $D^+$ mesons are determined as a function of tra… ▽ More The production of prompt $D^+_{s}$ and $D^+$ mesons is measured by the LHCb experiment in proton-lead ($p\mathrm{Pb}$) collisions in both the forward ($1.5<y^*<4.0$) and backward ($-5.0<y^*<-2.5$) rapidity regions at a nucleon-nucleon center-of-mass energy of $\sqrt {s_{\mathrm{NN}}}=8.16\,$TeV. The nuclear modification factors of both $D^+_{s}$ and $D^+$ mesons are determined as a function of transverse momentum, $p_{\mathrm{T}}$, and rapidity. In addition, the $D^+_{s}$ to $D^+$ cross-section ratio is measured as a function of the charged particle multiplicity in the event. An enhanced $D^+_{s}$ to $D^+$ production in high-multiplicity events is observed for the whole measured $p_{\mathrm{T}}$ range, in particular at low $p_{\mathrm{T}}$ and backward rapidity, where the significance exceeds six standard deviations. This constitutes the first observation of strangeness enhancement in charm quark hadronization in high-multiplicity $p\mathrm{Pb}$ collisions. The results are also qualitatively consistent with the presence of quark coalescence as an additional charm quark hadronization mechanism in high-multiplicity proton-lead collisions. △ Less

Submitted 4 September, 2024; v1 submitted 14 November, 2023; originally announced November 2023.

Comments: All figures and tables, along with machine-readable versions and any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2023-021.html (LHCb public pages)

Report number: LHCb-PAPER-2023-021, CERN-EP-2023-236

Journal ref: Phys. Rev. D 110, L031105 (2024)

Fraction of $χ_c$ decays in prompt $J/ψ$ production measured in pPb collisions at $\sqrt{s_{NN}}=8.16$ TeV

Authors: LHCb collaboration, R. Aaij, A. S. W. Abdelmotteleb, C. Abellan Beteta, F. Abudinén, T. Ackernley, B. Adeva, M. Adinolfi, P. Adlarson, C. Agapopoulou, C. A. Aidala, Z. Ajaltouni, S. Akar, K. Akiba, P. Albicocco, J. Albrecht, F. Alessio, M. Alexander, A. Alfonso Albero, Z. Aliouche, P. Alvarez Cartelle, R. Amalric, S. Amato, J. L. Amey, Y. Amhis , et al. (1078 additional authors not shown)

Abstract: The fraction of $χ_{c1}$ and $χ_{c2}$ decays in the prompt $J/ψ$ yield, $F_{χc}=σ_{χ_c \to J/ψ}/σ_{J/ψ}$, is measured by the LHCb detector in pPb collisions at $\sqrt{s_{NN}}=8.16$ TeV. The study covers the forward ($1.5<y^*<4.0$) and backward ($-5.0<y^*<-2.5$) rapidity regions, where $y^*$ is the $J/ψ$ rapidity in the nucleon-nucleon center-of-mass system. Forward and backward rapidity samples co… ▽ More The fraction of $χ_{c1}$ and $χ_{c2}$ decays in the prompt $J/ψ$ yield, $F_{χc}=σ_{χ_c \to J/ψ}/σ_{J/ψ}$, is measured by the LHCb detector in pPb collisions at $\sqrt{s_{NN}}=8.16$ TeV. The study covers the forward ($1.5<y^*<4.0$) and backward ($-5.0<y^*<-2.5$) rapidity regions, where $y^*$ is the $J/ψ$ rapidity in the nucleon-nucleon center-of-mass system. Forward and backward rapidity samples correspond to integrated luminosities of 13.6 $\pm$ 0.3 nb$^{-1}$ and 20.8 $\pm$ 0.5 nb$^{-1}$, respectively. The result is presented as a function of the $J/ψ$ transverse momentum $p_{T,J/ψ}$ in the range 1$<p_{T, J/ψ}<20$ GeV/$c$. The $F_{χc}$ fraction at forward rapidity is compatible with the LHCb measurement performed in $pp$ collisions at $\sqrt{s}=7$ TeV, whereas the result at backward rapidity is 2.4 $σ$ larger than in the forward region for $1<p_{T, J/ψ}<3$ GeV/$c$. The increase of $F_{χc}$ at low $p_{T, J/ψ}$ at backward rapidity is compatible with the suppression of the $ψ$(2S) contribution to the prompt $J/ψ$ yield. The lack of in-medium dissociation of $χ_c$ states observed in this study sets an upper limit of 180 MeV on the free energy available in these pPb collisions to dissociate or inhibit charmonium state formation. △ Less

Submitted 2 November, 2023; originally announced November 2023.

Comments: All figures and tables, along with machine-readable versions and any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2023-028.html (LHCb public pages)

Report number: LHCb-PAPER-2023-028, CERN-EP-2023-224

Journal ref: Phys. Rev. Lett. 132 (2024) 102302

Production of $η$ and $η'$ mesons in $pp$ and $p$Pb collisions

Authors: LHCb collaboration, R. Aaij, A. S. W. Abdelmotteleb, C. Abellan Beteta, F. Abudinén, T. Ackernley, B. Adeva, M. Adinolfi, P. Adlarson, C. Agapopoulou, C. A. Aidala, Z. Ajaltouni, S. Akar, K. Akiba, P. Albicocco, J. Albrecht, F. Alessio, M. Alexander, A. Alfonso Albero, Z. Aliouche, P. Alvarez Cartelle, R. Amalric, S. Amato, J. L. Amey, Y. Amhis , et al. (1080 additional authors not shown)

Abstract: The production of $η$ and $η'$ mesons is studied in proton-proton and proton-lead collisions collected with the LHCb detector. Proton-proton collisions are studied at center-of-mass energies of $5.02$ and $13~{\rm TeV}$, and proton-lead collisions are studied at a center-of-mass energy per nucleon of $8.16~{\rm TeV}$. The studies are performed in center-of-mass rapidity regions… ▽ More The production of $η$ and $η'$ mesons is studied in proton-proton and proton-lead collisions collected with the LHCb detector. Proton-proton collisions are studied at center-of-mass energies of $5.02$ and $13~{\rm TeV}$, and proton-lead collisions are studied at a center-of-mass energy per nucleon of $8.16~{\rm TeV}$. The studies are performed in center-of-mass rapidity regions $2.5<y_{\rm c.m.}<3.5$ (forward rapidity) and $-4.0<y_{\rm c.m.}<-3.0$ (backward rapidity) defined relative to the proton beam direction. The $η$ and $η'$ production cross sections are measured differentially as a function of transverse momentum for $1.5<p_{\rm T}<10~{\rm GeV}$ and $3<p_{\rm T}<10~{\rm GeV}$, respectively. The differential cross sections are used to calculate nuclear modification factors. The nuclear modification factors for $η$ and $η'$ mesons agree at both forward and backward rapidity, showing no significant evidence of mass dependence. The differential cross sections of $η$ mesons are also used to calculate $η/π^0$ cross section ratios, which show evidence of a deviation from the world average. These studies offer new constraints on mass-dependent nuclear effects in heavy-ion collisions, as well as $η$ and $η'$ meson fragmentation. △ Less

Submitted 13 February, 2025; v1 submitted 26 October, 2023; originally announced October 2023.

Comments: All figures and tables, along with machine-readable versions and any supplementary material and additional information, are available at https://lhcbproject.web.cern.ch/Publications/p/LHCb-PAPER-2023-030.html (LHCb public pages)

Report number: LHCb-PAPER-2023-030, CERN-EP-2023-228

Journal ref: Phys. Rev. C109 (2024), 024907

Multi-alpha Boson Gas state in Fusion Evaporation Reaction and Three-body Force

Authors: Taofeng Wang, Ziming Li, R. B. Wiringa, Minliang Liu, Jiansong Wang, Yanyun Yang, Qinghua He, Zhiyu Sun, Chengjian Lin, M. Assié, Y. Ayyad, D. Beaumel, Zhen Bai, Fangfang Duan, Zhihao Gao, Song Guo, Yue Hu, Wei Jiang, F. Kobayashi, Chengui Lu, Junbing Ma, Peng Ma, P. Napolitani, G. Verde, Jianguo Wang , et al. (11 additional authors not shown)

Abstract: The experimental evidence for the $α$ Boson gas state in the $^{11}$C+$^{12}$C$\rightarrow$$^{23}$Mg$^{\ast}$ fusion evaporation reaction is presented. By measuring the $α$ emission spectrum with multiplicity 2 and 3, we provide insight into the existence of a three-body force among $α$ particles. The observed spectrum exhibited distinct tails corresponding to $α$ particles emitted in pairs and tr… ▽ More The experimental evidence for the $α$ Boson gas state in the $^{11}$C+$^{12}$C$\rightarrow$$^{23}$Mg$^{\ast}$ fusion evaporation reaction is presented. By measuring the $α$ emission spectrum with multiplicity 2 and 3, we provide insight into the existence of a three-body force among $α$ particles. The observed spectrum exhibited distinct tails corresponding to $α$ particles emitted in pairs and triplets consistent well with the model-calculations of AV18-UX and chiral effective field theory of NV2-3-la*, indicating the formation of $α$ clusters with three-body force in the Boson gas state. △ Less

Submitted 6 October, 2023; originally announced October 2023.

Comments: 7 pages, 6 figures

Aspect of Clusters Correlation at Light Nuclei Excited State

Authors: Ziming Li, Jie Zhu, Taofeng Wang, Minliang Liu, Jiansong Wang, Yanyun Yang, Chengjian Lin, Zhiyu Sun, Qinghua He, M. Assié, Y. Ayyad, D. Beaumel, Zhen Bai, Fangfang Duan, Zhihao Gao, Song Guo, Yue Hu, Wei Jiang, F. Kobayashi, Chengui Lu, Junbing Ma, Peng Ma, P. Napolitani, G. Verde, Jianguo Wang , et al. (11 additional authors not shown)

Abstract: The correlation of $αα$ was probed via measuring the transverse momentum $p_{T}$ and width $δp_{T}$ of one $α$, for the first time, which represents the spatial and dynamical essentialities of the initial coupling state in $^{8}$Be nucleus. The weighted interaction vertex of 3$α$ reflected by the magnitudes of their relative momentums and relative emission angles proves the isosceles triangle conf… ▽ More The correlation of $αα$ was probed via measuring the transverse momentum $p_{T}$ and width $δp_{T}$ of one $α$, for the first time, which represents the spatial and dynamical essentialities of the initial coupling state in $^{8}$Be nucleus. The weighted interaction vertex of 3$α$ reflected by the magnitudes of their relative momentums and relative emission angles proves the isosceles triangle configuration for 3$α$ at the high excited energy analogous Hoyle states. △ Less

Submitted 6 October, 2023; originally announced October 2023.

Comments: 8 pages, 9 figures