-
Observation and branching fraction measurements of $χ_{cJ}\to p \bar p K^0_S K^0_S$
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. (705 additional authors not shown)
Abstract:
Based on $(2.712\pm0.014)\times10^9$ $ψ(3686)$ events collected with the BESIII detector, the decays $χ_{cJ} \to p \bar{p} K^{0}_{S} K^{0}_{S}$ ($J=0,1,2$) are observed for the first time with statistical significances exceeding $5σ$. The measured branching fractions are $\mathcal{B}(χ_{c0}\to p \bar p K^{0}_{S} K^{0}_{S})=(6.94\pm0.30\pm0.38)\times10^{-5}$,…
▽ More
Based on $(2.712\pm0.014)\times10^9$ $ψ(3686)$ events collected with the BESIII detector, the decays $χ_{cJ} \to p \bar{p} K^{0}_{S} K^{0}_{S}$ ($J=0,1,2$) are observed for the first time with statistical significances exceeding $5σ$. The measured branching fractions are $\mathcal{B}(χ_{c0}\to p \bar p K^{0}_{S} K^{0}_{S})=(6.94\pm0.30\pm0.38)\times10^{-5}$, $\mathcal{B}(χ_{c1}\to p \bar p K^{0}_{S} K^{0}_{S})=(1.30\pm0.12\pm0.08)\times10^{-5}$, and $\mathcal{B}(χ_{c2}\to p \bar p K^{0}_{S} K^{0}_{S})=(2.54\pm0.17\pm0.15)\times10^{-5}$, where the first uncertainties are statistical and the second systematic. Combining these results with the branching fractions of $χ_{cJ} \to p\bar{p} K^+K^-$ from a previous BESIII measurement, we determine the ratios of the branching fractions, $\frac{{\mathcal B}(χ_{c0,1,2}\to p\bar p K^+K^-)}{{\mathcal B}(χ_{c0,1,2}\to p\bar p K_S^0 K_S^0)}$, to be $1.8 \pm 0.1 \pm 0.3$, $9.8 \pm 0.9 \pm 1.7$ and $7.7 \pm 0.7 \pm 1.1$, respectively. These values differ significantly from the predictions of isospin symmetry.
△ Less
Submitted 22 December, 2025;
originally announced December 2025.
-
A comprehensive analysis of the $B^0\to K^{*0}μ^+μ^-$ decay
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,
M. Akthar,
P. Albicocco,
J. Albrecht,
R. Aleksiejunas,
F. Alessio,
P. Alvarez Cartelle,
R. Amalric,
S. Amato,
J. L. Amey,
Y. Amhis
, et al. (1177 additional authors not shown)
Abstract:
An analysis of the $B^{0}\rightarrow K^{*0}(\to K^+ π^-)μ^{+}μ^{-}$ decay is presented using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 8.4 fb$^{-1}$. The full set of $CP$-averaged and $CP$-asymmetric angular observables is determined in bins of the invariant mass squared of the dimuon system, as well as the branching fraction relati…
▽ More
An analysis of the $B^{0}\rightarrow K^{*0}(\to K^+ π^-)μ^{+}μ^{-}$ decay is presented using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 8.4 fb$^{-1}$. The full set of $CP$-averaged and $CP$-asymmetric angular observables is determined in bins of the invariant mass squared of the dimuon system, as well as the branching fraction relative to the $B^{0}\rightarrow J/ψ(\toμ^{+}μ^{-})K^+π^-$ decay. For the first time, the full set of observables pertaining to the $K^+π^-$ S-wave contribution to the final state are presented and consideration is given to effects arising from the mass of the muons. The measurements of the $CP$-averaged observables and the branching fractions continue to exhibit the pattern of tensions with the Standard Model predictions that have been seen in previous analyses that use part of the dataset considered in this study. The extracted $CP$-asymmetry observables show no significant deviations from zero.
△ Less
Submitted 19 December, 2025;
originally announced December 2025.
-
Cross sections measurement of $e^+e^-\to Ξ(1530)^0\barΞ^0 + c.c.$ and search for $ψ(3770)\toΞ(1530)^0\barΞ^0 + c.c.$
Authors:
BESIII Colaboration,
:,
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. B. Bertani,
D. Bettoni,
F. Bianchi,
E. Bianco,
A. Bortone,
I. Boyko,
R. A. Briere,
A. Brueggemann
, et al. (680 additional authors not shown)
Abstract:
Using $e^+e^-$ collision data collected with the BESIII detector corresponding to an integrated luminosity of 44.2 fb$^{-1}$, we measure the Born cross sections for the process $e^+e^- \to Ξ(1530)^{0} \barΞ^{0} + c.c.$ at forty-eight center-of-mass energies between 3.51 and 4.95 GeV. The potential signal from non-$D\bar{D}$ decays for $ψ(3770)$, i.e. $ψ(3770)\to Ξ(1530)^{0} \barΞ^{0}+ c.c.$, is in…
▽ More
Using $e^+e^-$ collision data collected with the BESIII detector corresponding to an integrated luminosity of 44.2 fb$^{-1}$, we measure the Born cross sections for the process $e^+e^- \to Ξ(1530)^{0} \barΞ^{0} + c.c.$ at forty-eight center-of-mass energies between 3.51 and 4.95 GeV. The potential signal from non-$D\bar{D}$ decays for $ψ(3770)$, i.e. $ψ(3770)\to Ξ(1530)^{0} \barΞ^{0}+ c.c.$, is investigated by fitting the dressed cross section, no obvious signal is found. The upper limit of $\mathcal{B}(ψ(3770) \to Ξ(1530)^{0} \barΞ^{0}$) at 90\% confidence level is given.
△ Less
Submitted 19 December, 2025;
originally announced December 2025.
-
Measurements of the Absolute Branching Fraction of the Semileptonic Decay $\mathbf{Ξ^{-}\rightarrow Λe^- \barν_{e}}$ and the Axial Charge of the $\mathbfΞ^{-}$
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. B. Bertani,
D. Bettoni,
F. Bianchi,
E. Bianco,
A. Bortone,
I. Boyko,
R. A. Briere,
A. Brueggemann,
H. Cai
, et al. (683 additional authors not shown)
Abstract:
Using $(10087\pm44)\times10^6$ $J/ψ$ events collected with the BESIII detector, we study the semileptonic decay $Ξ^{-}\rightarrow Λe^- \barν_{e}$ for the first time at an electron-positron collider. The absolute branching fraction is determined for the first time to be $(3.60\pm0.40_{\mathrm{stat}}\pm0.10_{\mathrm{syst}})\times10^{-4}$, which is 3.9 standard deviations below the world average. In…
▽ More
Using $(10087\pm44)\times10^6$ $J/ψ$ events collected with the BESIII detector, we study the semileptonic decay $Ξ^{-}\rightarrow Λe^- \barν_{e}$ for the first time at an electron-positron collider. The absolute branching fraction is determined for the first time to be $(3.60\pm0.40_{\mathrm{stat}}\pm0.10_{\mathrm{syst}})\times10^{-4}$, which is 3.9 standard deviations below the world average. In addition, using an 11-dimensional angular analysis, the axial-vector to vector coupling $g_{av}$ is determined to be $0.18\pm0.07_{\mathrm{stat}}\pm0.02_{\mathrm{syst}}$. These results are used to test various SU(3)-flavour effective models. Under the SU(3)-flavour symmetry limit, the axial charge is found to be $g_A^H = 0.22\pm0.08_{\mathrm{stat}}\pm0.02_{\mathrm{syst}}$. Despite using only 5\% of the statistics of previous experiments, this analysis achieves a comparable precision for the axial charge.
△ Less
Submitted 17 December, 2025;
originally announced December 2025.
-
Search for the decays $X(3872)\to K_{S}^{0}K^{\pm}π^{\mp}$ and $K^*(892)\bar{K}$ at BESIII
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,
X. L. Bao,
V. Batozskaya,
K. Begzsuren,
N. Berger,
M. Berlowski,
M. B. Bertani,
D. Bettoni,
F. Bianchi,
E. Bianco,
A. Bortone,
I. Boyko,
R. A. Briere,
A. Brueggemann
, et al. (684 additional authors not shown)
Abstract:
Using a 10.9 fb$^{-1}$ data sample collected by the BESIII detector at center-of-mass energies from 4.16 to 4.34 GeV, we search for the charmless decays $X(3872) \to K_{S}^{0}K^{\pm}π^{\mp}$ and $K^*(892)\bar{K}$, where the $X(3872)$ is produced via the radiative process $e^+e^- \to γX(3872)$. No significant signal is observed. We set upper limits on the relative branching fractions…
▽ More
Using a 10.9 fb$^{-1}$ data sample collected by the BESIII detector at center-of-mass energies from 4.16 to 4.34 GeV, we search for the charmless decays $X(3872) \to K_{S}^{0}K^{\pm}π^{\mp}$ and $K^*(892)\bar{K}$, where the $X(3872)$ is produced via the radiative process $e^+e^- \to γX(3872)$. No significant signal is observed. We set upper limits on the relative branching fractions $\mathcal{B}[X(3872)\to K_S K^{\pm} π^{\mp}]/\mathcal{B}[X(3872)\toπ^+π^- J/ψ] <0.07$ and $\mathcal{B}[X(3872)\to K^* (892)\bar{K}]/\mathcal{B}[X(3872)\to π^+π^- J/ψ] <0.10$ at the 90$\%$ confidence level. Additionally, upper limits on the product of the cross section $σ[e^+e^-\toγX(3872)]$ and the branching fractions $\mathcal{B}[X(3872)\to K_{S}^{0}K^{\pm}π^{\mp}]$ and $\mathcal{B}[X(3872)\to K^*(892)\bar{K}]$ are reported at each energy point. In all cases, $K^*(892)\bar{K}$ refers to the sum of the modes $K^*(892)^+K^{-}+\text{c.c.}$ and $K^*(892)^0\bar{K}^0+\text{c.c.}$, where c.c. denotes the corresponding charge-conjugate modes.
△ Less
Submitted 17 December, 2025;
originally announced December 2025.
-
Search for heavy neutral leptons in B-meson decays
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,
R. Aleksiejunas,
F. Alessio,
P. Alvarez Cartelle,
R. Amalric,
S. Amato,
J. L. Amey,
Y. Amhis,
L. An
, et al. (1177 additional authors not shown)
Abstract:
A search for long-lived heavy neutral leptons produced in B-meson decays and decaying to a $ μ^\pm π^\mp$ final state is performed with data collected by the LHCb experiment in proton-proton collisions at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of $5\,\mathrm{fb}^{-1}$. The results are interpreted in both lepton-number-conserving and lepton-number-violating sce…
▽ More
A search for long-lived heavy neutral leptons produced in B-meson decays and decaying to a $ μ^\pm π^\mp$ final state is performed with data collected by the LHCb experiment in proton-proton collisions at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of $5\,\mathrm{fb}^{-1}$. The results are interpreted in both lepton-number-conserving and lepton-number-violating scenarios. No significant excess is observed. Constraints are placed on the squared mixing element $|U_{μN}|^2$ to the active muon neutrino, under the assumption that couplings to other lepton flavours are negligible, in the mass range of $1.6$-$5.5$ GeV.
△ Less
Submitted 16 December, 2025;
originally announced December 2025.
-
Measurements of the branching fractions of $χ_{cJ}\to φφη, φφη^{\prime}$ and $φK^+K^-η$
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. B. Bertani,
D. Bettoni,
F. Bianchi,
E. Bianco,
A. Bortone,
I. Boyko,
R. A. Briere,
A. Brueggemann,
H. Cai
, et al. (681 additional authors not shown)
Abstract:
Using a sample of $(2712.4 \pm 14.3)\times 10^6 ~ψ$(3686) events collected by the BESIII detector at the BEPCII collider, we measure the branching fractions of the decays $χ_{cJ}\to φφη,~φφη^{\prime}$, and~$φK^+K^-η$ ($J = 0, 1, 2$). The obtained branching fractions are $\mathcal{B}(χ_{c0} \to φφη) = (7.40 \pm 0.23 \pm 0.55)\times10^{-4}$,…
▽ More
Using a sample of $(2712.4 \pm 14.3)\times 10^6 ~ψ$(3686) events collected by the BESIII detector at the BEPCII collider, we measure the branching fractions of the decays $χ_{cJ}\to φφη,~φφη^{\prime}$, and~$φK^+K^-η$ ($J = 0, 1, 2$). The obtained branching fractions are $\mathcal{B}(χ_{c0} \to φφη) = (7.40 \pm 0.23 \pm 0.55)\times10^{-4}$, $\mathcal{B}(χ_{c1} \to φφη) = (3.33 \pm 0.14 \pm 0.25)\times10^{-4}$, $\mathcal{B}(χ_{c2} \to φφη) = (5.46 \pm 0.17 \pm 0.40)\times10^{-4}$, $\mathcal{B}(χ_{c0} \to φφη^\prime) = (2.96 \pm 0.23 \pm 0.29)\times10^{-4}$, $\mathcal{B}(χ_{c1} \to φφη^\prime) = (0.69 \pm 0.10 \pm 0.08)\times10^{-4}$, $\mathcal{B}(χ_{c2} \to φφη^\prime) = (0.65 \pm 0.09 \pm 0.07)\times10^{-4}$, $\mathcal{B}(χ_{c0} \to φK^+K^-η) = (1.23 \pm 0.08 \pm 0.10)\times10^{-4}$, $\mathcal{B}(χ_{c1} \to φK^+K^-η) = (1.00 \pm 0.07 \pm 0.07)\times10^{-4}$, and $\mathcal{B}(χ_{c2} \to φK^+K^-η) = (1.82 \pm 0.09 \pm 0.14)\times10^{-4}$, where $K^+K^-$ is not from the decay of a $φ$ meson, the first uncertainties are statistical and the second systematic. The branching fractions of $χ_{cJ}\to φφη$ are measured with precision improved by factors of $1.5-1.9$, and those of $χ_{cJ}\to φφη^\prime$ and $φK^+K^-η$ are measured for the first time.
△ Less
Submitted 16 December, 2025;
originally announced December 2025.
-
Amplitude Analysis and Branching Fraction Measurement of $D^+ \to π^+π^0π^0$
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. B. Bertani,
D. Bettoni,
F. Bianchi,
E. Bianco,
A. Bortone,
I. Boyko,
R. A. Briere,
A. Brueggemann,
H. Cai
, et al. (684 additional authors not shown)
Abstract:
We present the first amplitude analysis of the hadronic decay $D^+\toπ^+π^0π^0$, using $e^{+}e^{-}$ collision data collected with the BESIII detector at a center-of-mass energy of 3.773~GeV, corresponding to an integrated luminosity of 20.3~fb$^{-1}$. The fit fractions of the intermediate processes are measured, in which the $D^+ \to ρ(770)^+π^0$ component is found to be dominant with a branching…
▽ More
We present the first amplitude analysis of the hadronic decay $D^+\toπ^+π^0π^0$, using $e^{+}e^{-}$ collision data collected with the BESIII detector at a center-of-mass energy of 3.773~GeV, corresponding to an integrated luminosity of 20.3~fb$^{-1}$. The fit fractions of the intermediate processes are measured, in which the $D^+ \to ρ(770)^+π^0$ component is found to be dominant with a branching fraction of $(3.08\kern0.15em\pm\kern0.15em0.10_{\rm stat.}\pm0.05_{\rm syst.})\times10^{-3}$. Based on the amplitude analysis, the branching fraction of $D^+ \to π^+π^0π^0$ is measured to be $(4.84\kern0.1em\pm\kern0.1em0.05_{\rm stat.}\kern0.1em\pm\kern0.1em0.05_{\rm syst.})\times10^{-3}$. In addition, the CP asymmetries, both for specific amplitudes and integrated over the entire phase space, are measured.
△ Less
Submitted 13 December, 2025;
originally announced December 2025.
-
Measurement of the top-quark production cross-section and charge asymmetry at LHCb
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,
M. Akthar,
P. Albicocco,
J. Albrecht,
R. Aleksiejunas,
F. Alessio,
P. Alvarez Cartelle,
R. Amalric,
S. Amato,
J. L. Amey,
Y. Amhis
, et al. (1170 additional authors not shown)
Abstract:
The first measurements of the top- and antitop-quark differential production cross-sections and the top-quark charge asymmetry in the forward region are presented, using proton-proton collision data collected by the LHCb experiment at a centre-of-mass energy of 13 TeV corresponding to an integrated luminosity of 5.4 $fb^{-1}$. The total production cross-sections of top and antitop quarks are also…
▽ More
The first measurements of the top- and antitop-quark differential production cross-sections and the top-quark charge asymmetry in the forward region are presented, using proton-proton collision data collected by the LHCb experiment at a centre-of-mass energy of 13 TeV corresponding to an integrated luminosity of 5.4 $fb^{-1}$. The total production cross-sections of top and antitop quarks are also determined. Measurements are performed using the $μ+b\text{-jet}$ final state within a fiducial region defined by a $b\text{-jet}$ $p_{\text{T, jet}}>50$ GeV and pseudorapidity $2.2<η_{\text{jet}}<4.0$,, with the muon from the $W$-boson decay required to have $p_{\text{T},μ}>25$ GeV and pseudorapidity $2.0<η_μ<4.5$. The muon and $b$-jet system must satisfy $p_{T}(μ+\text{jet}) > 20$ GeV. The measured integrated production cross-sections for the top and antitop quarks are $σ_{t} = 0.95 \pm 0.04 \pm 0.08 \pm 0.02$ pb, $σ_{\bar{t}} = 0.81 \pm 0.03 \pm 0.07 \pm 0.02$ pb, where the first uncertainty is statistical, the second systematic, and the third accounts for the luminosity uncertainty. The top-quark charge asymmetry is measured to be $A_C^{t} = 0.08 \pm 0.03 \pm 0.01$, where the first uncertainty is statistical and the second is systematic. These results are consistent with next-to-leading-order Standard Model predictions.
△ Less
Submitted 12 December, 2025;
originally announced December 2025.
-
First measurement of the absolute branching fractions of $Σ^+$ nonleptonic decays and test of the $ΔI = 1/2$ rule % $Σ^+ \to p π^0$ and $Σ^+ \to n π^+$
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,
X. L. Bao,
V. Batozskaya,
K. Begzsuren,
N. Berger,
M. Berlowski,
M. B. Bertani,
D. Bettoni,
F. Bianchi,
E. Bianco,
A. Bortone,
I. Boyko,
R. A. Briere,
A. Brueggemann
, et al. (689 additional authors not shown)
Abstract:
Based on $(10087 \pm 44) \times 10^6$ $J/ψ$ events collected by the BESIII detector at the center-of-mass energy $\sqrt{s} = 3.097$ GeV, the first absolute measurement of the branching fractions for the decays $Σ^+ \to p π^0$ and $Σ^+ \to n π^+$ is performed. The branching fractions are determined to be $B_{Σ^+ \to p π^0} = (49.79 \pm 0.06 \pm 0.22)\%$ and…
▽ More
Based on $(10087 \pm 44) \times 10^6$ $J/ψ$ events collected by the BESIII detector at the center-of-mass energy $\sqrt{s} = 3.097$ GeV, the first absolute measurement of the branching fractions for the decays $Σ^+ \to p π^0$ and $Σ^+ \to n π^+$ is performed. The branching fractions are determined to be $B_{Σ^+ \to p π^0} = (49.79 \pm 0.06 \pm 0.22)\%$ and $B_{Σ^+ \to n π^+} = (49.87 \pm 0.05 \pm 0.29)\%$, where the first uncertainties are statistical and the second systematic. These results show significant deviations from the PDG values for both decays, with differences of 4.4$σ$ for $Σ^+ \to p π^0$ and 3.4$σ$ for $Σ^+ \to n π^+$. Furthermore, the $ΔI = 1/2$ rule is tested in nonleptonic $Σ^\pm$ decays. The observed results deviate from zero by more than $5σ$, indicating the presence of the $ΔI = 3/2$ transition amplitude in the $Σ$ hyperon decays.
△ Less
Submitted 10 December, 2025;
originally announced December 2025.
-
Precision measurement of CP violation and branching fractions in $B^{\pm} \to K^0_{\mathrm{S}} h^{\pm}$ $(h = π, K)$ decays and search for the rare decay $B_c^{\pm} \to K^0_{\mathrm{S}} K^{\pm}$
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,
M. Akthar,
P. Albicocco,
J. Albrecht,
R. Aleksiejunas,
F. Alessio,
P. Alvarez Cartelle,
R. Amalric,
S. Amato,
J. L. Amey,
Y. Amhis,
L. An
, et al. (1174 additional authors not shown)
Abstract:
An analysis of the decays $B^{\pm} \to K^0_{\mathrm{S}} π^{\pm}$ and $B^{\pm} \to K^0_{\mathrm{S}} K^{\pm}$ is performed using proton--proton collision data collected by the LHCb experiment at a center-of-mass energy of 13TeV, corresponding to an integrated luminosity of 5.4fb$^{-1}$. The CP asymmetries are determined to be…
▽ More
An analysis of the decays $B^{\pm} \to K^0_{\mathrm{S}} π^{\pm}$ and $B^{\pm} \to K^0_{\mathrm{S}} K^{\pm}$ is performed using proton--proton collision data collected by the LHCb experiment at a center-of-mass energy of 13TeV, corresponding to an integrated luminosity of 5.4fb$^{-1}$. The CP asymmetries are determined to be ${\cal A}^{CP}(B^{\pm} \to K^0_{\mathrm{S}} π^{\pm}) = -0.028 \pm 0.009 \pm 0.009$ and ${\cal A}^{CP}(B^{\pm} \to K^0_{\mathrm{S}} K^{\pm}) = 0.118 \pm 0.062 \pm 0.031$, and the branching-fraction ratio is measured to be ${\cal B}(B^{\pm} \to K^0_{\mathrm{S}} K^{\pm}) / {\cal B}(B^{\pm} \to K^0_{\mathrm{S}} π^{\pm}) = 0.055 \pm 0.004 \pm 0.002$, where the first uncertainties are statistical and the second systematic. These results are the most precise measurements of these quantities to date. A search for the rare decay $B_c^{\pm} \to K^0_{\mathrm{S}} K^{\pm}$ is also performed. No significant signal is observed, and the upper limit on the product of the branching-fraction ratio ${\cal B}(B_c^{\pm} \to K^0_{\mathrm{S}} K^{\pm}) / {\cal B}(B^{\pm} \to K^0_{\mathrm{S}} π^{\pm})$ and the fragmentation-fraction ratio $f_c/f_u$ is set to be 0.015 (0.016) at the 90% (95%) confidence level.
△ Less
Submitted 9 December, 2025;
originally announced December 2025.
-
Measurement of the branching fraction of $η\to μ^+ μ^-$ and search for $η\to e^+ e^-$
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. (706 additional authors not shown)
Abstract:
We analyze the decay of $η\rightarrow \ell^+\ell^-(\ell=e, μ)$ via $J/ψ\rightarrowγη'$ and $η'\rightarrowπ^+π^-η$, based on (10087 $\pm$ 44) $\times$ 10$^{6}$ $J/ψ$ events collected with the BESIII detector at the BEPCII storage rings. The branching fraction of $η\rightarrowμ^+ μ^-$ is measured to be $(5.8 \pm 1.0_{\rm stat} \pm 0.2_{\rm syst}) \times 10^{-6}$, which is consistent with the previou…
▽ More
We analyze the decay of $η\rightarrow \ell^+\ell^-(\ell=e, μ)$ via $J/ψ\rightarrowγη'$ and $η'\rightarrowπ^+π^-η$, based on (10087 $\pm$ 44) $\times$ 10$^{6}$ $J/ψ$ events collected with the BESIII detector at the BEPCII storage rings. The branching fraction of $η\rightarrowμ^+ μ^-$ is measured to be $(5.8 \pm 1.0_{\rm stat} \pm 0.2_{\rm syst}) \times 10^{-6}$, which is consistent with the previous measurements and theoretical expectations. In addition, no significant $η\to e^+e^-$ signal is observed in the $e^+ e^-$ invariant mass spectrum, and an improved upper limit of ${\cal B}(η\to e^+ e^-) < 2.2 \times 10^{-7}$ is set at 90\% confidence level.
△ Less
Submitted 7 December, 2025;
originally announced December 2025.
-
Evidence for the semileptonic decays $Λ_c^{+} \to Σ^{\pm} π^{\mp} e^+ ν_e$
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. (679 additional authors not shown)
Abstract:
Using $4.5\, fb^{-1}$ of $e^+e^-$ collision data collected by the BESIII detector at center-of-mass energies between $4.600$ and $4.699\,GeV$, we search for the semileptonic decays $Λ_c^{+} \to Σ^{+} π^{-} e^+ ν_e$ and $Λ_c^{+} \to Σ^{-} π^{+} e^+ ν_e$ for the first time. Assuming their branching fractions are equal under isospin symmetry, evidence for $Λ_c^{+} \to Σ^{\pm} π^{\mp} e^+ ν_e$ is repo…
▽ More
Using $4.5\, fb^{-1}$ of $e^+e^-$ collision data collected by the BESIII detector at center-of-mass energies between $4.600$ and $4.699\,GeV$, we search for the semileptonic decays $Λ_c^{+} \to Σ^{+} π^{-} e^+ ν_e$ and $Λ_c^{+} \to Σ^{-} π^{+} e^+ ν_e$ for the first time. Assuming their branching fractions are equal under isospin symmetry, evidence for $Λ_c^{+} \to Σ^{\pm} π^{\mp} e^+ ν_e$ is reported with a significance of $3.6σ$. The corresponding branching fraction is measured to be $\mathcal{B}(Λ_c^{+} \to Σ^\pmπ^\mp e^+ν_e) = (7.7^{+2.5}_{-2.3_{\rm stat.}}\pm1.3_{\rm syst.})\times 10^{-4}$, which is consistent with quark model predictions within two standard deviations.
△ Less
Submitted 4 December, 2025;
originally announced December 2025.
-
Measurement of the branching fractions and longitudinal polarisations of $B^0_{(s)} \to K^{*0} \kern 0.18em \overline{\kern -0.18em K}{}^{*0}$ decays
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,
R. Aleksiejunas,
F. Alessio,
P. Alvarez Cartelle,
R. Amalric,
S. Amato,
J. L. Amey,
Y. Amhis,
L. An
, et al. (1180 additional authors not shown)
Abstract:
A time- and flavour-integrated amplitude analysis of $B^0$ and $B^0_s$ decays to the $(K^+π^-)(K^-π^+)$ final state in the $K^*(892)^0 \kern 0.18em \overline{\kern -0.18em K}{}^{*}(892)^0$ region is presented, using $pp$ collision data recorded with the LHCb detector in 2011--2018, corresponding to an integrated luminosity of $9\,\text{fb}^{-1}$. The branching fractions of the $B^0$ and $B^0_s$ de…
▽ More
A time- and flavour-integrated amplitude analysis of $B^0$ and $B^0_s$ decays to the $(K^+π^-)(K^-π^+)$ final state in the $K^*(892)^0 \kern 0.18em \overline{\kern -0.18em K}{}^{*}(892)^0$ region is presented, using $pp$ collision data recorded with the LHCb detector in 2011--2018, corresponding to an integrated luminosity of $9\,\text{fb}^{-1}$. The branching fractions of the $B^0$ and $B^0_s$ decays are measured relative to the $B^0 \to D^-π^+$ and $B^0_s \to D^-_s π^+$ modes, respectively. The corresponding longitudinal polarisation fractions are found to be $f_L^{d} = 0.600 \pm 0.022 \pm 0.017$ and $f_L^{s} = 0.159 \pm 0.010 \pm 0.007$, where the uncertainties are statistical and systematic, respectively. The theory-motivated $L_{K^{*0} \kern 0.18em \overline{\kern -0.18em K}{}^{*0}}$ observable is found to be $L_{K^{*0} \kern 0.18em \overline{\kern -0.18em K}{}^{*0}} = 4.92 \pm 0.55 \pm 0.47 \pm 0.02 \pm 0.10$, where the uncertainties are statistical, systematic, due to uncertainty of external mass and lifetime measurements, and due to knowledge of the fragmentation fraction ratio, respectively. This confirms the previously reported tension between experimental determinations and theoretical predictions of longitudinal polarisation in $B \to VV$ decays.
△ Less
Submitted 4 December, 2025;
originally announced December 2025.
-
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 4 December, 2025;
originally announced December 2025.
-
Measurement of the hyperon weak radiative decay $Ξ^0\toγΣ^0$ at BESIII
Authors:
BESIII Collaboration,
M. Ablikim,
M. N. Achasov,
P. Adlarson,
X. C. Ai,
R. Aliberti,
A. Amoroso,
M. R. An,
Q. An,
Y. Bai,
O. Bakina,
I. Balossino,
Y. Ban,
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
, et al. (604 additional authors not shown)
Abstract:
The hyperon weak radiative decay $Ξ^0\toγΣ^0$ is measured via the process $J/ψ\toΞ^0\barΞ^0$. The absolute branching fraction of $Ξ^0\toγΣ^0$ is determined to be $(3.69\pm 0.21_{\text{stat}}\pm0.12_{\text{syst}})\times 10^{-3}$, based on $(10.087\pm 0.044)\times 10^{9}$ $J/ψ$ events collected with the BESIII detector operating at the BEPCII collider. The decay asymmetry parameter is measured, with…
▽ More
The hyperon weak radiative decay $Ξ^0\toγΣ^0$ is measured via the process $J/ψ\toΞ^0\barΞ^0$. The absolute branching fraction of $Ξ^0\toγΣ^0$ is determined to be $(3.69\pm 0.21_{\text{stat}}\pm0.12_{\text{syst}})\times 10^{-3}$, based on $(10.087\pm 0.044)\times 10^{9}$ $J/ψ$ events collected with the BESIII detector operating at the BEPCII collider. The decay asymmetry parameter is measured, with a complete angular analysis of the cascade decay chain, to be $α_γ = -0.807\pm 0.095_{\text{stat}}\pm 0.011_{\text{syst}}$.
△ Less
Submitted 3 December, 2025;
originally announced December 2025.
-
Observation of the rare baryonic decay $B^{+}\rightarrow p \bar{\itΛ}$ and measurement of its weak decay parameter
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,
R. Aleksiejunas,
F. Alessio,
P. Alvarez Cartelle,
R. Amalric,
S. Amato,
J. L. Amey,
Y. Amhis,
L. An
, et al. (1179 additional authors not shown)
Abstract:
The first observation of the decay $B^{+}\rightarrow p \bar{\itΛ}$ is presented, using proton-proton collision data collected by the LHCb experiment between 2016 and 2018 at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of $5.4\,\mathrm{fb}^{-1}$. The signal significance exceeds seven standard deviations. Using the…
▽ More
The first observation of the decay $B^{+}\rightarrow p \bar{\itΛ}$ is presented, using proton-proton collision data collected by the LHCb experiment between 2016 and 2018 at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of $5.4\,\mathrm{fb}^{-1}$. The signal significance exceeds seven standard deviations. Using the $B^{+} \rightarrow K^{\mathrm{0}}_{\mathrm{S}} π^{+}$ decay as a normalization channel, the branching fraction is measured and combined with previous LHCb results based on data collected at 7 and 8 TeV in 2011 and 2012, yielding $\mathcal{B}(B^{+}\rightarrow p \bar{\itΛ})=(1.24\pm 0.17\pm 0.05\pm 0.03)\times 10^{-7}$, where the first uncertainty is statistical, the second is systematic, and the third comes from the uncertainty on the branching fraction of the normalization channel. The $B^{+}\rightarrow p \bar{\itΛ}$ weak decay parameter is measured to be $α_B = 0.87_{-0.29}^{+0.26} \pm 0.09$, indicating the presence of comparable S-wave and P-wave decay amplitudes.
△ Less
Submitted 3 December, 2025; v1 submitted 29 November, 2025;
originally announced December 2025.
-
Study of the reactions $\bar{n} p \to 2π^{+}π^{-}$, $2π^{+}π^{-}π^{0}$, and $2π^{+}π^{-}2π^{0}$ using $J/ψ\to p π^{-}\bar{n}$
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,
X. L. Bao,
V. Batozskaya,
K. Begzsuren,
N. Berger,
M. Berlowski,
M. B. Bertani,
D. Bettoni,
F. Bianchi,
E. Bianco,
A. Bortone,
I. Boyko,
R. A. Briere,
A. Brueggemann
, et al. (687 additional authors not shown)
Abstract:
We report an experimental investigation of the reactions $\bar{n} p \to 2π^{+}π^{-}$, $\bar{n} p \to 2π^{+}π^{-}π^{0}$, and $\bar{n} p \to 2π^{+}π^{-}2π^{0}$ using $(10.087 \pm 0.044) \times 10^{9}$ $J/ψ$ events collected with the BESIII detector at the BEPCII storage ring. The antineutron ($\bar{n}$) is produced in the decay $J/ψ\to p π^{-} \bar{n}$ with studied momentum from 200~MeV/$c$ to 1174~…
▽ More
We report an experimental investigation of the reactions $\bar{n} p \to 2π^{+}π^{-}$, $\bar{n} p \to 2π^{+}π^{-}π^{0}$, and $\bar{n} p \to 2π^{+}π^{-}2π^{0}$ using $(10.087 \pm 0.044) \times 10^{9}$ $J/ψ$ events collected with the BESIII detector at the BEPCII storage ring. The antineutron ($\bar{n}$) is produced in the decay $J/ψ\to p π^{-} \bar{n}$ with studied momentum from 200~MeV/$c$ to 1174~MeV/$c$, while the target proton originates from the hydrogen nuclei in the cooling oil of the beam pipe. This novel method pioneers the study of $\bar{n}$-nucleon interactions at an $e^{+}e^{-}$ collider, providing the first experimental data for $\bar{n}$ momenta exceeding 800~MeV/$c$.
△ Less
Submitted 26 November, 2025;
originally announced November 2025.
-
First observation of the $\overline{B}_{s}^{0}\toΛ_{c}^{+}\overlineΛ_{c}{}^{-}$ decay and evidence for the $\overline{B}^{0}\toΛ_{c}^{+}\overlineΛ_{c}{}^{-}$ decay
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,
M. Akthar,
P. Albicocco,
J. Albrecht,
R. Aleksiejunas,
F. Alessio,
P. Alvarez Cartelle,
R. Amalric,
S. Amato,
J. L. Amey,
Y. Amhis
, et al. (1181 additional authors not shown)
Abstract:
A search is presented for the two-body charmed baryonic decays $\overline{B}_{(s)}^{0}\toΛ_{c}^{+}\overlineΛ_{c}{}^{-}$, using a data sample collected by the LHCb experiment during 2011--2012 and 2015--2018 corresponding to an integrated luminosity of $9\,\mathrm{fb}^{-1}$. The first observation of the $\overline{B}_{s}^{0}\toΛ_{c}^{+}\overlineΛ_{c}{}^{-}$ decay is reported with $6.2σ$ significanc…
▽ More
A search is presented for the two-body charmed baryonic decays $\overline{B}_{(s)}^{0}\toΛ_{c}^{+}\overlineΛ_{c}{}^{-}$, using a data sample collected by the LHCb experiment during 2011--2012 and 2015--2018 corresponding to an integrated luminosity of $9\,\mathrm{fb}^{-1}$. The first observation of the $\overline{B}_{s}^{0}\toΛ_{c}^{+}\overlineΛ_{c}{}^{-}$ decay is reported with $6.2σ$ significance, along with $4.3σ$ evidence for the $\overline{B}^{0}\toΛ_{c}^{+}\overlineΛ_{c}{}^{-}$ decay. The branching fractions are measured to be $\mathcal{B}{}(\overline{B}^{0}\toΛ_{c}^{+}\overlineΛ_{c}{}^{-}) = (1.01^{+0.27}_{-0.28} \pm 0.08 \pm 0.15) \times 10^{-5}$ and $\mathcal{B}{}(\overline{B}_{s}^{0}\toΛ_{c}^{+}\overlineΛ_{c}{}^{-}) = (5.0 \pm 1.3 \pm 0.5 \pm 0.8) \times 10^{-5}$, where the first uncertainty is statistical, the second systematic, and the third due to external inputs. These results provide novel experimental inputs for the theoretical framework describing two-body baryonic decays of $B$ mesons via $W$-emission and $W$-exchange mechanisms.
△ Less
Submitted 27 November, 2025; v1 submitted 25 November, 2025;
originally announced November 2025.
-
Observation and investigation of the $T_{c\bar{c}1}(4430)^{+}$ structure in $B^{+} \to ψ(2S) K_{\text{S}}^{0} π^{+}$ decays
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,
M. Akthar,
P. Albicocco,
J. Albrecht,
R. Aleksiejunas,
F. Alessio,
P. Alvarez Cartelle,
R. Amalric,
S. Amato,
J. L. Amey,
Y. Amhis
, et al. (1181 additional authors not shown)
Abstract:
The first four-dimensional amplitude analysis of the $B^{+} \to ψ(2S) K_{\text{S}}^{0} π^{+}$ decay is performed with proton-proton collision data collected by the LHCb experiment at $\sqrt{s} = 13~\rm{TeV}$, corresponding to an integrated luminosity of $5.4~\rm{fb^{-1}}$. The data cannot be fully explained by $B^{+} \to ψ(2S) K^{*+}$ contributions alone. A significantly better description of the…
▽ More
The first four-dimensional amplitude analysis of the $B^{+} \to ψ(2S) K_{\text{S}}^{0} π^{+}$ decay is performed with proton-proton collision data collected by the LHCb experiment at $\sqrt{s} = 13~\rm{TeV}$, corresponding to an integrated luminosity of $5.4~\rm{fb^{-1}}$. The data cannot be fully explained by $B^{+} \to ψ(2S) K^{*+}$ contributions alone. A significantly better description of the data is obtained by adding a $T_{c\bar{c}}^{+}$ contribution decaying to $ψ(2S)π^{+}$. The properties of the $T_{c\bar{c}}^{+}$ structure are consistent with the exotic state $T_{c\bar{c}1}(4430)^{+}$ reported in the isospin-related $\bar{B}^{0} \to ψ(2S) K^{-} π^{+}$ decay. Effects of a possible $T_{c\bar{c}1}(4430)^{+} \to \bar{D}_{1}^{*}(2600)^{0} D^{+}$ decay mode on the $T_{c\bar{c}1}(4430)^{+} \to ψ(2S)π^{+}$ mass distribution are investigated through a Flatté parametrization, providing constraints on the relative decay strength. A description of the $T_{c\bar{c}1}(4430)^{+}$ structure using the triangle singularity mechanism is studied and also found to be consistent with the data.
△ Less
Submitted 26 November, 2025; v1 submitted 25 November, 2025;
originally announced November 2025.
-
Differential decay rate of $B^+ \to J/ψK^+$ with the LHCb Upgrade I experiment
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,
M. Akthar,
P. Albicocco,
J. Albrecht,
R. Aleksiejunas,
F. Alessio,
P. Alvarez Cartelle,
R. Amalric,
S. Amato,
J. L. Amey,
Y. Amhis
, et al. (1177 additional authors not shown)
Abstract:
The normalised decay rate of $B^+ \to J/ψ(\to μ^+μ^-) K^+$ is measured as a function of the lepton helicity angle using a data sample corresponding to an integrated luminosity of $1.1 \text{fb}^{-1}$ collected during October 2024 with the upgraded (Upgrade I) LHCb detector. This angular distribution can be parameterised by two coefficients, the forward-backward asymmetry, $A_{FB}$, and the flatnes…
▽ More
The normalised decay rate of $B^+ \to J/ψ(\to μ^+μ^-) K^+$ is measured as a function of the lepton helicity angle using a data sample corresponding to an integrated luminosity of $1.1 \text{fb}^{-1}$ collected during October 2024 with the upgraded (Upgrade I) LHCb detector. This angular distribution can be parameterised by two coefficients, the forward-backward asymmetry, $A_{FB}$, and the flatness parameter, $F_{H}$, whose values are constrained by conservation of angular momentum. These coefficients are measured both integrated and differentially across various kinematic and detector-response variables, and the results are found to be in good agreement with expectations. These measurements show that the detector response of the LHCb Upgrade I experiment is understood to the precision required to reliably extract the angular coefficients associated with rare $b \to s μ^+μ^-$ and $b \to d μ^+μ^-$ transitions, which are particularly sensitive to physics beyond the Standard Model.
△ Less
Submitted 20 November, 2025;
originally announced November 2025.
-
Search for the charmonium weak decay $J/ψ\to\bar{D}^0\bar{K}^{*0}+{\rm c.c.}$
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. (706 additional authors not shown)
Abstract:
Based on a sample of $(10087\pm44)\times10^6$ $J/ψ$ events collected at the center-of-mass energy $\sqrt{s}$ = 3.0969 GeV with the BESIII detector, we search for the charmonium rare weak decay $J/ψ\to\bar{D}^0\bar{K}^{*0}+{\rm c.c.}$. No significant signal is observed, and the upper limit on its decay branching fraction at the 90% confidence level is set as $1.9\times10^{-7}$, improving the sensit…
▽ More
Based on a sample of $(10087\pm44)\times10^6$ $J/ψ$ events collected at the center-of-mass energy $\sqrt{s}$ = 3.0969 GeV with the BESIII detector, we search for the charmonium rare weak decay $J/ψ\to\bar{D}^0\bar{K}^{*0}+{\rm c.c.}$. No significant signal is observed, and the upper limit on its decay branching fraction at the 90% confidence level is set as $1.9\times10^{-7}$, improving the sensitivity of the previous best limit by an order of magnitude.
△ Less
Submitted 20 November, 2025;
originally announced November 2025.
-
Branching fraction measurement of the $\mathitΛ \to p μ^- \overlineν_μ$ decay
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,
R. Aleksiejunas,
F. Alessio,
P. Alvarez Cartelle,
R. Amalric,
S. Amato,
J. L. Amey,
Y. Amhis,
L. An
, et al. (1185 additional authors not shown)
Abstract:
A measurement of the branching fraction for the decay $\mathitΛ \to p μ^- \overlineν_μ$ is presented using $\textit{pp}$ collision data collected by the LHCb experiment at a centre-of-mass energy of 13 TeV. The analysis is based on data recorded between 2016 and 2018, corresponding to an integrated luminosity of $5.4 \ \text{fb}^{-1}$. The result is obtained using $\mathitΛ \to p π^-$ decays as a…
▽ More
A measurement of the branching fraction for the decay $\mathitΛ \to p μ^- \overlineν_μ$ is presented using $\textit{pp}$ collision data collected by the LHCb experiment at a centre-of-mass energy of 13 TeV. The analysis is based on data recorded between 2016 and 2018, corresponding to an integrated luminosity of $5.4 \ \text{fb}^{-1}$. The result is obtained using $\mathitΛ \to p π^-$ decays as a normalisation channel. The measured branching fraction is $B(\mathitΛ \to p μ^- \overlineν_μ)= (1.462 \pm 0.016 \pm 0.100 \pm 0.011 ) \times 10^{-4}$, where the uncertainties are statistical, systematic, and due to the limited knowledge of the normalisation mode branching fraction, respectively. This result improves the precision of the branching fraction measurement by a factor of two compared to the previous best measurement and sets a more stringent bound on lepton flavour universality in $s \to u$ quark transitions. It is consistent with previous measurements, and the extracted lepton flavour universality test observable, $R^{μe} = \frac{Γ(\mathitΛ \to p μ^- \overlineν_μ)}{Γ(\mathitΛ \to p e^- \overlineν_e)} = 0.175 \pm 0.012$, agrees with the Standard Model prediction.
△ Less
Submitted 19 November, 2025;
originally announced November 2025.
-
Search for the lepton number violating process $Ξ^- \rightarrow Σ^+ e^- e^- +c.c.$
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,
X. L. Bao,
V. Batozskaya,
K. Begzsuren,
N. Berger,
M. Berlowski,
M. B. Bertani,
D. Bettoni,
F. Bianchi,
E. Bianco,
A. Bortone,
I. Boyko,
R. A. Briere,
A. Brueggemann
, et al. (691 additional authors not shown)
Abstract:
We present a search for the lepton number violating decay $Ξ^-\rightarrowΣ^+e^-e^- +c.c.$ with $(10087\pm44)\times10^6$ $J/ψ$ events collected by the BESIII detector at the BEPCII collider. Employing a blind analysis strategy, no significant signal is observed above the expected background yield. The upper limit on the branching fraction is determined to be…
▽ More
We present a search for the lepton number violating decay $Ξ^-\rightarrowΣ^+e^-e^- +c.c.$ with $(10087\pm44)\times10^6$ $J/ψ$ events collected by the BESIII detector at the BEPCII collider. Employing a blind analysis strategy, no significant signal is observed above the expected background yield. The upper limit on the branching fraction is determined to be ${\rm Br}(Ξ^-\rightarrowΣ^+e^-e^-+c.c.)< 2.0\times10^{-5}$ at the $90\%$ confidence level.
△ Less
Submitted 19 November, 2025;
originally announced November 2025.
-
Measurement of charged-hadron distributions in heavy-flavor jets in proton-proton 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,
M. Akthar,
P. Albicocco,
J. Albrecht,
R. Aleksiejunas,
F. Alessio,
P. Alvarez Cartelle,
R. Amalric,
S. Amato,
J. L. Amey,
Y. Amhis
, et al. (1172 additional authors not shown)
Abstract:
Charged-hadron distributions in heavy-flavor jets are measured in proton-proton collisions at a center-of-mass energy of $\sqrt{s}$ = 13 TeV collected by the LHCb experiment. Distributions of the longitudinal momentum fraction, transverse momentum, and radial profile of charged hadrons are measured separately in beauty and charm jets. The distributions are compared to those previously measured by…
▽ More
Charged-hadron distributions in heavy-flavor jets are measured in proton-proton collisions at a center-of-mass energy of $\sqrt{s}$ = 13 TeV collected by the LHCb experiment. Distributions of the longitudinal momentum fraction, transverse momentum, and radial profile of charged hadrons are measured separately in beauty and charm jets. The distributions are compared to those previously measured by the LHCb collaboration in jets produced back-to-back with a $Z$ boson, which in the forward region are primarily light-quark-initiated, to compare the hadronization mechanisms of heavy and light quarks. The observed differences between the heavy- and light-jet distributions are consistent with the heavy-quark dynamics expected to arise from the dead-cone effect, as well as with a hard fragmentation of the heavy-flavor hadron as previously measured in single-hadron fragmentation functions. This measurement provides additional constraints for the extraction of collinear and transverse-momentum-dependent heavy-flavor fragmentation functions and offers another approach to probing the mechanisms that govern heavy-flavor hadronization.
△ Less
Submitted 13 November, 2025;
originally announced November 2025.
-
Search for $K_{\mathrm{S(L)}}^{0} \rightarrow π^{+}π^{-}μ^{+}μ^{-}$ decays at LHCb
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,
R. Aleksiejunas,
F. Alessio,
P. Alvarez Cartelle,
R. Amalric,
S. Amato,
J. L. Amey,
Y. Amhis,
L. An
, et al. (1180 additional authors not shown)
Abstract:
A search for $K_{\mathrm{S(L)}}^{0} \rightarrow π^{+}π^{-}μ^{+}μ^{-}$ decays is performed using proton-proton collision data collected by the LHCb experiment at a centre-of-mass energy of $13\,\mathrm{TeV}$, corresponding to an integrated luminosity of $5.4\,\mathrm{fb^{-1}}$. No $K_{\mathrm{S(L)}}^{0} \rightarrow π^{+}π^{-}μ^{+}μ^{-}$ signals are found and upper limits are set for the first time…
▽ More
A search for $K_{\mathrm{S(L)}}^{0} \rightarrow π^{+}π^{-}μ^{+}μ^{-}$ decays is performed using proton-proton collision data collected by the LHCb experiment at a centre-of-mass energy of $13\,\mathrm{TeV}$, corresponding to an integrated luminosity of $5.4\,\mathrm{fb^{-1}}$. No $K_{\mathrm{S(L)}}^{0} \rightarrow π^{+}π^{-}μ^{+}μ^{-}$ signals are found and upper limits are set for the first time on the branching fractions $\mathcal{B}(K_\text{S}^{0} \rightarrow π^{+}π^{-}μ^{+}μ^{-}) < 1.4 \times 10^{-9}$ and $\mathcal{B}(K_\text{L}^{0} \rightarrow π^{+}π^{-}μ^{+}μ^{-}) < 6.6 \times 10^{-7}$, at the 90% confidence level.
△ Less
Submitted 4 November, 2025;
originally announced November 2025.
-
Amplitude analysis and branching fraction measurement of the decay $D^0 \to K^0_Sπ^0π^0$
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. (703 additional authors not shown)
Abstract:
An amplitude analysis of the decay $D^0 \to K_S^0 π^0 π^0$ is performed to determine the relative magnitudes and phases of different intermediate processes. The analysis uses $e^+e^-$ collision data collected at the center-of-mass energy of 3.773 GeV by the BESIII detector corresponding to an integrated luminosity of 20.3 $\rm fb^{-1}$. The absolute branching fraction of $D^0 \to K^0_S π^0 π^0$ is…
▽ More
An amplitude analysis of the decay $D^0 \to K_S^0 π^0 π^0$ is performed to determine the relative magnitudes and phases of different intermediate processes. The analysis uses $e^+e^-$ collision data collected at the center-of-mass energy of 3.773 GeV by the BESIII detector corresponding to an integrated luminosity of 20.3 $\rm fb^{-1}$. The absolute branching fraction of $D^0 \to K^0_S π^0 π^0$ is measured to be $(1.026 \pm 0.008_{\rm{stat.}} \pm 0.009_{\rm{syst.}}) \%$. The dominant intermediate process is $D^0 \to \bar{K}^{*}(892)^{0}(\to K^0_S π^0) π^0$, with a branching fraction of $(4.22\pm0.09_{\rm{stat.}}\pm0.14_{\rm{syst.}})\times 10^{-3}$.
△ Less
Submitted 28 October, 2025;
originally announced October 2025.
-
Search for the charmonium semi-leptonic weak decay $J/ψ\rightarrow D_s^-e^+ν_e+c.c.$
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. B. Bertani,
D. Bettoni,
F. Bianchi,
E. Bianco,
A. Bortone,
I. Boyko,
R. A. Briere,
A. Brueggemann,
H. Cai
, et al. (683 additional authors not shown)
Abstract:
Using a data sample of $(10087 \pm 44) \times 10^6$ $J/ψ$ events collected with the BESIII detector at a centre-of-mass energy of $\sqrt{s}=3.097\ \textrm{GeV}$, a dedicated search for the charmonium semileptonic weak decay $J/ψ\rightarrow D_s^-e^+ν_e + \text{c.c.}$ is performed. No significant signal is observed. An upper limit on the branching fraction is set at…
▽ More
Using a data sample of $(10087 \pm 44) \times 10^6$ $J/ψ$ events collected with the BESIII detector at a centre-of-mass energy of $\sqrt{s}=3.097\ \textrm{GeV}$, a dedicated search for the charmonium semileptonic weak decay $J/ψ\rightarrow D_s^-e^+ν_e + \text{c.c.}$ is performed. No significant signal is observed. An upper limit on the branching fraction is set at $\mathcal{B}(J/ψ\rightarrow D_s^- e^+ ν_e + \text{c.c.}) < 1.0 \times 10^{-7}$ at the 90\% confidence level. This result improves upon previous constraints by an order of magnitude, representing the most stringent experimental limit to date. It thus provides a critical test of Standard Model predictions and new physics scenarios in heavy-quark dynamics.
△ Less
Submitted 28 October, 2025;
originally announced October 2025.
-
Test of $CP$ Symmetry in the Neutral Decays of $Λ$ via $J/ψ\toΛ\barΛ$
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. B. Bertani,
D. Bettoni,
F. Bianchi,
E. Bianco,
A. Bortone,
I. Boyko,
R. A. Briere,
A. Brueggemann,
H. Cai
, et al. (683 additional authors not shown)
Abstract:
Using $(10087\pm44)\times10^{6}$ $J/ψ$ events collected with the BESIII detector, a full angular distribution analysis is carried out on the process $J/ψ\rightarrowΛ\barΛ\rightarrow nπ^{0}\bar{p}π^{+}+c.c.$ The decay parameters $α_{0}$ for $Λ\rightarrow nπ^{0}$ and $\barα_{0}$ for $\barΛ\rightarrow \bar{n}π^{0}$ are measured to be $0.668\pm0.007\pm0.002$ and $-0.677\pm0.007\pm0.003$, respectively,…
▽ More
Using $(10087\pm44)\times10^{6}$ $J/ψ$ events collected with the BESIII detector, a full angular distribution analysis is carried out on the process $J/ψ\rightarrowΛ\barΛ\rightarrow nπ^{0}\bar{p}π^{+}+c.c.$ The decay parameters $α_{0}$ for $Λ\rightarrow nπ^{0}$ and $\barα_{0}$ for $\barΛ\rightarrow \bar{n}π^{0}$ are measured to be $0.668\pm0.007\pm0.002$ and $-0.677\pm0.007\pm0.003$, respectively, yielding the most precise test for $CP$ symmetry of neutral decays of $Λ$, $A_{CP}^{0}=(α_{0}+\barα_{0})/(α_{0}-\barα_{0})$, to be $-0.006\pm0.007\pm0.002$. The ratios $α_{0}/α_{-}$ and $\barα_{0}/α_{+}$ are determined to be $0.884\pm0.013\pm0.006$ and $0.885\pm0.013\pm0.004$, where $α_{-}$ and $α_{+}$ are the decay parameters of $Λ\rightarrow pπ^{-}$ and $\barΛ\rightarrow\bar{p}π^{+}$, respectively. The ratios, found to be smaller than unity by more than $5σ$, confirm the presence of the $ΔI = 3/2$ transition in the $Λ$ and $\barΛ$ decays, which is expected to improve the theoretical calculations for strong and weak phases, and $A_{CP}$, in hyperon decays. In all results, the first and second uncertainties are statistical and systematic, respectively.
△ Less
Submitted 28 October, 2025;
originally announced October 2025.
-
Precision Measurement of $D_{s}^{*+} - D_{s}^{+}$ Mass Difference with $D_{s}^{*+} \to D_{s}^{+}(\to K^{+} K^{-} π^{+})π^{0}$
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. B. Bertani,
D. Bettoni,
F. Bianchi,
E. Bianco,
A. Bortone,
I. Boyko,
R. A. Briere,
A. Brueggemann,
H. Cai
, et al. (681 additional authors not shown)
Abstract:
We measure the mass difference between $D_{s}^{*+}$ and $D_{s}^{+}$, $Δm_s$, using the decay chain $D_{s}^{*+} \to D_{s}^{+}(\to K^{+} K^{-} π^{+})π^{0}$, utilizing $e^+e^-$ annihilation data corresponding to an integrated luminosity of 3.19 fb$^{-1}$ collected at a center-of-mass energy of 4.178 GeV with the BESIII detector. The measured value of…
▽ More
We measure the mass difference between $D_{s}^{*+}$ and $D_{s}^{+}$, $Δm_s$, using the decay chain $D_{s}^{*+} \to D_{s}^{+}(\to K^{+} K^{-} π^{+})π^{0}$, utilizing $e^+e^-$ annihilation data corresponding to an integrated luminosity of 3.19 fb$^{-1}$ collected at a center-of-mass energy of 4.178 GeV with the BESIII detector. The measured value of $Δm_s = [144\,201.9 \pm 44.2({\rm stat.}) \pm 29.9({\rm syst.}) \pm 15.0({\rm PDG})]$ keV/$c^2$ is about seven times more precise than the current Particle Data Group average, where the last uncertainty is from the Particle Data Group average of the $D^{*+} - D^{+}$ mass difference.
△ Less
Submitted 23 October, 2025;
originally announced October 2025.
-
Evidence of Transverse Polarization of $Ξ^0$ Hyperon in $ψ(3686)\rightarrowΞ^0\barΞ^0$
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. B. Bertani,
D. Bettoni,
F. Bianchi,
E. Bianco,
A. Bortone,
I. Boyko,
R. A. Briere,
A. Brueggemann,
H. Cai
, et al. (681 additional authors not shown)
Abstract:
Using $(2.712\pm0.014)\times10^{9}$ $ψ(3686)$ events collected with the BESIII detector at the BEPCII collider, we report an evidence of $Ξ^{0}$ transverse polarization with a significance of 4.4$σ$, and a precise measurement of the branching fraction of $ψ(3686)\toΞ^{0}\barΞ^{0}$. The weak decay parameters ($φ_{Ξ^0/\barΞ^{0}}$, $α_{Ξ^0/\barΞ^{0}}$) and the angular distribution ($α_ψ$) are also me…
▽ More
Using $(2.712\pm0.014)\times10^{9}$ $ψ(3686)$ events collected with the BESIII detector at the BEPCII collider, we report an evidence of $Ξ^{0}$ transverse polarization with a significance of 4.4$σ$, and a precise measurement of the branching fraction of $ψ(3686)\toΞ^{0}\barΞ^{0}$. The weak decay parameters ($φ_{Ξ^0/\barΞ^{0}}$, $α_{Ξ^0/\barΞ^{0}}$) and the angular distribution ($α_ψ$) are also measured with higher precision compared to the previous measurements. Furthermore, two the $C\!P$ observables are also determined to be $A^{Ξ^0}_{C\!P} = -0.014 \pm 0.030 \pm 0.010$ and $Δφ^{Ξ^0}_{C\!P} = 0.000 \pm 0.028 \pm 0.003$ rad, which are still consistent with $C\!P$ conservation at 1$σ$ level under the current statistics.
△ Less
Submitted 22 October, 2025;
originally announced October 2025.
-
Measurements of absolute branching fractions of $D^{0(+)}\to KKKπ$ decays
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. (700 additional authors not shown)
Abstract:
Using an $e^+e^-$ sample of $20.3\,\rm fb^{-1}$ collected at the center-of-mass energy $\sqrt{s}=$ 3.773 GeV with the BESIII detector, we report measurements of several four-body hadronic decays of the $D$ mesons. The absolute branching fractions are determined to be ${\mathcal B}(D^0\to K^0_S K^+K^-π^0 )=( 18.4^{+2.6}_{-2.5}\pm 2.4)\times 10^{-5}$,…
▽ More
Using an $e^+e^-$ sample of $20.3\,\rm fb^{-1}$ collected at the center-of-mass energy $\sqrt{s}=$ 3.773 GeV with the BESIII detector, we report measurements of several four-body hadronic decays of the $D$ mesons. The absolute branching fractions are determined to be ${\mathcal B}(D^0\to K^0_S K^+K^-π^0 )=( 18.4^{+2.6}_{-2.5}\pm 2.4)\times 10^{-5}$, ${\mathcal B}(D^0\to K^0_S K^0_S K^-π^+ )=( 12.9^{+1.7}_{-1.6}\pm 2.5)\times 10^{-5}$, ${\mathcal B}(D^0\to K^0_S K^0_S K^+π^-)=(5.7^{+1.2}_{-1.1}\pm 1.3)\times 10^{-5}$, ${\mathcal B}(D^0\to K^+K^-K^-π^+ )=(17.4^{+1.8}_{-1.7}\pm { 2.2})\times 10^{-5}$, and ${\mathcal B}(D^+\to K^0_S K^+K^-π^+)=(13.8^{+2.4}_{-2.2}\pm 2.5)\times 10^{-5}$. Furthermore, significant $φ$ signals are found in the decay channels involving $K^+K^-$ pair, and the corresponding branching fractions are measured as ${\mathcal B}(D^0\to φK^0_Sπ^0 )=( 22.7^{+5.4}_{-5.1}\pm 3.7)\times 10^{-5}$, ${\mathcal B}(D^0\to φK^-π^+ )=(25.2^{+3.5}_{-3.3}\pm 4.6)\times 10^{-5}$, ${\mathcal B}(D^+\to φK^0_Sπ^+)=(16.5 ^{+6.0}_{-5.3}\pm 2.6 )\times 10^{-5}$. The branching fractions of
$D^0\to K^0_S K^+K^-π^0$, $D^0\to φK^0_Sπ^0$, and $D^+\to φK^0_S π^+$ are measured for the first time, and those of $D^0\to K^0_S K^0_SK^-π^+$, $D^0\to K^0_S K^0_SK^+π^-$, $D^0\to K^+K^-K^-π^+$, $D^0\to φK^-π^+$, and $D^+\to K^0_S K^+K^-π^+$ are measured with improved precision. The first uncertainties are statistical and the second are systematic.
△ Less
Submitted 23 October, 2025; v1 submitted 21 October, 2025;
originally announced October 2025.
-
Search for a hypothetical gauge boson and dark photons in charmonium transitions
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. B. Bertani,
D. Bettoni,
F. Bianchi,
E. Bianco,
A. Bortone,
I. Boyko,
R. A. Briere,
A. Brueggemann,
H. Cai
, et al. (677 additional authors not shown)
Abstract:
We report a direct search for a new gauge boson, $X$, with a mass of $17~\text{MeV}/c^2$, which could explain the anomalous excess of $e^+e^-$ pairs observed in the $^8\text{Be}$ nuclear transitions. The search is conducted in the charmonium decay $χ_{cJ}\to X J/ψ~(J=0,1,2)$ via the radiative transition $ψ(3686)\toγχ_{cJ}$ using $\left(2712.4\pm 14.3 \right)\times 10^6$ $ψ(3686)$ events collected…
▽ More
We report a direct search for a new gauge boson, $X$, with a mass of $17~\text{MeV}/c^2$, which could explain the anomalous excess of $e^+e^-$ pairs observed in the $^8\text{Be}$ nuclear transitions. The search is conducted in the charmonium decay $χ_{cJ}\to X J/ψ~(J=0,1,2)$ via the radiative transition $ψ(3686)\toγχ_{cJ}$ using $\left(2712.4\pm 14.3 \right)\times 10^6$ $ψ(3686)$ events collected with the BESIII detector at the BEPCII collider. No significant signal is observed, and the new upper limit on the coupling strength of charm quark and the new gauge boson, $ε_c$, at $17~\text{MeV}/c^2$ is set to be $|ε_c|<1.2\times 10^{-2}$ at $90\%$ confidence level. We also report new constraints on the mixing strength $ε$ between the Standard Model photon and dark photon $γ^\prime$ in the mass range from $5~\text{MeV}/c^2$ to $300~\text{MeV}/c^2$. The upper limits at $90\%$ confidence level vary within $(2.5-17.5)\times 10^{-3}$ depending on the $γ^\prime $ mass.
△ Less
Submitted 18 October, 2025;
originally announced October 2025.
-
Study of the Magnetic Dipole Transition of $J/ψ\toγη_c$ via $η_c\to p\bar{p}$
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. (700 additional authors not shown)
Abstract:
Using $(10.087\pm0.044)\times10^9$ $J/ψ$ events collected with the BESIII detector at the $e^+e^-$ BEPCII collider, we present the first amplitude analysis of $J/ψ\toγp\bar{p}$ with the $p\bar p$ invariant mass in the $η_c$ mass region $[2.70,3.05]$~GeV/$c^2$. The product branching fraction $\mathcal{B}(J/ψ\toγη_c)\times\mathcal{B}(η_c\to p\bar{p})$ is precisely determined to be…
▽ More
Using $(10.087\pm0.044)\times10^9$ $J/ψ$ events collected with the BESIII detector at the $e^+e^-$ BEPCII collider, we present the first amplitude analysis of $J/ψ\toγp\bar{p}$ with the $p\bar p$ invariant mass in the $η_c$ mass region $[2.70,3.05]$~GeV/$c^2$. The product branching fraction $\mathcal{B}(J/ψ\toγη_c)\times\mathcal{B}(η_c\to p\bar{p})$ is precisely determined to be $(2.11\pm0.02_{\rm stat}\pm0.07_{\rm syst})\times10^{-5}$. Combining with the product branching fractions $\mathcal{B}(η_c\to p\bar{p})\times\mathcal{B}(η_c\to γγ)$ and $\mathcal{B}(J/ψ\toγη_c)\times\mathcal{B}(η_c\to γγ)$, the branching fractions of $\mathcal{B}(J/ψ\toγη_c)$ and $\mathcal{B}(η_c\toγγ)$ are calculated to be $(2.29\pm0.01_{\rm stat}\pm0.04_{\rm syst}\pm0.18_{\rm opbf})\%$ and $(2.28\pm0.01_{\rm stat}\pm0.04_{\rm syst}\pm0.18_{\rm opbf})\times10^{-4}$, respectively, which are consistent with the latest lattice quantum chromodynamics calculations. Here, opbf is the uncertainty from the other product branching fractions used in the calculation.
△ Less
Submitted 16 October, 2025;
originally announced October 2025.
-
Measurement of $C\!P$ asymmetry in $D^0 \to K^0_{\rm S} K^0_{\rm S}$ decays with the LHCb Upgrade I detector
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,
M. Akthar,
P. Albicocco,
J. Albrecht,
R. Aleksiejunas,
F. Alessio,
P. Alvarez Cartelle,
R. Amalric,
S. Amato,
J. L. Amey,
Y. Amhis
, et al. (1187 additional authors not shown)
Abstract:
A measurement of $C\!P$ asymmetry in $D^0 \to K^0_{\rm S} K^0_{\rm S}$ decays is reported, based on a data sample of proton-proton collisions collected with the LHCb Upgrade I detector in 2024 at a centre-of-mass energy of $13.6\,$TeV, corresponding to an integrated luminosity of $6.2\,\mathrm{fb}^{-1}$. The $D^0 \to K^0_{\rm S} π^+ π^-$ decay is used as calibration channel to cancel residual dete…
▽ More
A measurement of $C\!P$ asymmetry in $D^0 \to K^0_{\rm S} K^0_{\rm S}$ decays is reported, based on a data sample of proton-proton collisions collected with the LHCb Upgrade I detector in 2024 at a centre-of-mass energy of $13.6\,$TeV, corresponding to an integrated luminosity of $6.2\,\mathrm{fb}^{-1}$. The $D^0 \to K^0_{\rm S} π^+ π^-$ decay is used as calibration channel to cancel residual detection and production asymmetries. The time-integrated $C\!P$ asymmetry for the $D^0 \to K^0_{\rm S} K^0_{\rm S}$ mode is measured to be $$ {\cal A}^{C\!P} (D^0 \to K^0_{\rm S} K^0_{\rm S}) = (1.86 \pm 1.04\pm 0.41)\%, $$ where the first uncertainty is statistical, and the second is systematic. This is the most precise determination of this quantity to date.
△ Less
Submitted 16 October, 2025;
originally announced October 2025.
-
Searches for $B^0\to K^+π^-τ^+τ^-$ and $B_s^0\to K^+K^-τ^+τ^-$ decays
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,
M. Akthar,
P. Albicocco,
J. Albrecht,
R. Aleksiejunas,
F. Alessio,
P. Alvarez Cartelle,
R. Amalric,
S. Amato,
J. L. Amey,
Y. Amhis
, et al. (1182 additional authors not shown)
Abstract:
The first searches for $B^0\to K^+π^-τ^+τ^-$ and $B^0_s\to K^+K^-τ^+τ^-$ decays at the LHCb experiment are conducted with $pp$ collision data corresponding to an integrated luminosity of $5.4\textrm{ fb}^{-1}$. The tau leptons are reconstructed using the $τ^+\to μ^+\overlineν_τν_μ$ decay and the results are presented in bins of $K^+π^-$ or $K^+K^-$ mass. No signal is observed and upper limits are…
▽ More
The first searches for $B^0\to K^+π^-τ^+τ^-$ and $B^0_s\to K^+K^-τ^+τ^-$ decays at the LHCb experiment are conducted with $pp$ collision data corresponding to an integrated luminosity of $5.4\textrm{ fb}^{-1}$. The tau leptons are reconstructed using the $τ^+\to μ^+\overlineν_τν_μ$ decay and the results are presented in bins of $K^+π^-$ or $K^+K^-$ mass. No signal is observed and upper limits are set on the branching fractions. The searches result in the first upper limits for $B^0\to K^+π^-τ^+τ^-$ decays outside the $K^*(892)^0$ region in $K^+π^-$ mass and the first limits for $B^0_s\to K^+K^-τ^+τ^-$ decays. The searches are recast into limits on the decays $B^0\to K^*(892)^0τ^+τ^-$ and $B^0_s\to φ(1020)τ^+τ^-$, yielding $2.8\times10^{-4}$ ($2.5\times10^{-4}$) and $4.7\times10^{-4}$ ($4.1\times10^{-4}$) at the $95\%$ ($90\%$) confidence level, respectively. For the decay $B^0\to K^*(892)^0τ^+τ^-$, this result improves on the current best upper limit by an order of magnitude.
△ Less
Submitted 15 October, 2025;
originally announced October 2025.
-
First measurement of the cross sections for $e^{+}e^{-}\to K^{0}K^{-}π^{+}J/ψ+c.c.$ at $\sqrt{s}$ from 4.396 to 4.951 GeV
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. (705 additional authors not shown)
Abstract:
Using $e^+e^-$ collision data at 19 center-of-mass energies ranging from $4.396$ to $4.951~\mathrm{GeV}$ corresponding to a total integrated luminosity of $8.86~{\rm fb}^{-1}$ collected by the BESIII detector, the process $e^+e^-\to K^{0}K^-π^+ J/ψ+c.c.$ is observed for the first time, with a statistical significance of $9.4σ$ summing up all the data samples. For this process, the cross section an…
▽ More
Using $e^+e^-$ collision data at 19 center-of-mass energies ranging from $4.396$ to $4.951~\mathrm{GeV}$ corresponding to a total integrated luminosity of $8.86~{\rm fb}^{-1}$ collected by the BESIII detector, the process $e^+e^-\to K^{0}K^-π^+ J/ψ+c.c.$ is observed for the first time, with a statistical significance of $9.4σ$ summing up all the data samples. For this process, the cross section and the upper limit at the $90\%$ confidence level are reported at each of the 19 center-of-mass energies.~No statistically significant vector structures are observed in the cross section line shape, nor are any intermediate states of $Kπ$, $K\bar{K}$, $K\bar{K}π$, $KJ/ψ$, $πJ/ψ$, and $KπJ/ψ$ seen at individual energy points or in the combined data sample.
△ Less
Submitted 15 October, 2025;
originally announced October 2025.
-
First measurements of the branching fractions of $J/ψ\to Ξ^0\barΛK^0_S+c.c.$, $J/ψ\to Ξ^0\barΣ^0 K^0_S+c.c.$, and $J/ψ\to Ξ^0\barΣ^- K^++c.c.$
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. B. Bertani,
D. Bettoni,
F. Bianchi,
E. Bianco,
A. Bortone,
I. Boyko,
R. A. Briere,
A. Brueggemann,
H. Cai
, et al. (684 additional authors not shown)
Abstract:
By analyzing $(10087 \pm 44)\times10^6$ $J/ψ$ events collected with the BESIII detector at the BEPCII, the decays $J/ψ\to Ξ^0\barΛK^0_S+c.c.$, $J/ψ\to Ξ^0\barΣ^0 K^0_S+c.c.$, and $J/ψ\to Ξ^0\barΣ^- K^++c.c.$ are observed for the first time. Their branching fractions are determined to be $\mathcal{B}(J/ψ\to Ξ^0\barΛK^0_S+c.c.)=(3.76\pm 0.14\pm 0.23)\times10^{-5}$,…
▽ More
By analyzing $(10087 \pm 44)\times10^6$ $J/ψ$ events collected with the BESIII detector at the BEPCII, the decays $J/ψ\to Ξ^0\barΛK^0_S+c.c.$, $J/ψ\to Ξ^0\barΣ^0 K^0_S+c.c.$, and $J/ψ\to Ξ^0\barΣ^- K^++c.c.$ are observed for the first time. Their branching fractions are determined to be $\mathcal{B}(J/ψ\to Ξ^0\barΛK^0_S+c.c.)=(3.76\pm 0.14\pm 0.23)\times10^{-5}$, $\mathcal{B}(J/ψ\to Ξ^0\barΣ^0 K^0_S+c.c.)=(2.24\pm 0.32\pm 0.31)\times10^{-5}$, and $\mathcal{B}(J/ψ\to Ξ^0\barΣ^- K^++c.c.)=(5.64\pm 0.17\pm 0.28)\times10^{-5}$, where the first uncertainties are statistical and the second systematic.
△ Less
Submitted 17 December, 2025; v1 submitted 9 October, 2025;
originally announced October 2025.
-
First Measurement of the $D_s^+\rightarrow K^0μ^+ν_μ$ Decay
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. (700 additional authors not shown)
Abstract:
We report the first measurement of the semileptonic decay $D^+_s \rightarrow K^0μ^+ν_μ$, using a sample of $e^+e^-$ annihilation data corresponding to an integrated luminosity of $7.33~\mathrm{fb}^{-1}$ collected at center-of-mass energies between 4.128 to 4.226~GeV with the BESIII detector at the BEPCII collider. The branching fraction of the decay is measured to be…
▽ More
We report the first measurement of the semileptonic decay $D^+_s \rightarrow K^0μ^+ν_μ$, using a sample of $e^+e^-$ annihilation data corresponding to an integrated luminosity of $7.33~\mathrm{fb}^{-1}$ collected at center-of-mass energies between 4.128 to 4.226~GeV with the BESIII detector at the BEPCII collider. The branching fraction of the decay is measured to be $\mathcal{B}(D^+_s\rightarrow K^0μ^+ν_μ) = (2.89 \pm 0.27_{\rm stat} \pm 0.12_{\rm syst})\times 10^{-3}$, where the first uncertainty is statistical and the second is systematic. Based on a simultaneous fit to the partial decay rates in $q^2$ intervals measured in $D^+_s \rightarrow K^0μ^+ν_μ$ and $D^+_s \rightarrow K^0e^+ν_{e}$ decays, the product value of the form factor $f^{K^0}_{+}(0)$ and the Cabibbo-Kobayashi-Maskawa matrix element $|V_{cd}|$ is measured to be $f^{K^0}_{+}(0)|V_{cd}|=0.140\pm0.008_{\rm stat}\pm0.002_{\rm syst}$. Using $|V_{cd}|=0.22486\pm0.00068$ as an input, the hadronic form factor is determined to be $f^{K^0}_{+}(0)=0.623\pm0.036_{\rm stat} \pm 0.009_{\rm syst}$ at $q^2=0$. This is the most precise determination of $f^{K^0}_{+}(0)$ in the $D^+_s \rightarrow K^0$ transition to date. The measured branching fraction and form factor presented in this work provide the most stringent test on various non-perturbative theoretical calculations. Taking $f^{K^0}_{+}(0)=0.6307\pm0.0020$ from lattice calculations as an input, we obtain $|V_{cd}|=0.220\pm0.013_{\rm stat}\pm0.003_{\rm syst}\pm0.001_{\rm LQCD}$, which is the most precise determination of $|V_{cd}|$ using the $D_s^+\rightarrow K^0\ell^+ν_{\ell}$ decays. In addition, lepton flavor universality is tested for the first time with $D^+_s \rightarrow K^0\ell^+ν_{\ell}$ decays in full and separate $q^2$ intervals. No obvious violation is found.
△ Less
Submitted 7 October, 2025;
originally announced October 2025.
-
Study of charm mixing and CP violation with $D^0\to K^\pmπ^\mpπ^\pmπ^\mp$ decays
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,
R. Aleksiejunas,
F. Alessio,
P. Alvarez Cartelle,
R. Amalric,
S. Amato,
J. L. Amey,
Y. Amhis,
L. An
, et al. (1186 additional authors not shown)
Abstract:
A study of charm mixing and CP violation in $D^0\to K^\pmπ^\mpπ^\pmπ^\mp$ decays is performed using data collected by the LHCb experiment in proton-proton collisions from 2015 to 2018, corresponding to an integrated luminosity of 6$\text{fb}^{-1}$. The ratio of promptly produced $D^0\to K^+π^- π^+π^-$ to $D^0\to K^-π^+ π^-π^+$ decay rates is measured as a function of $D^0$ decay time, both inclusi…
▽ More
A study of charm mixing and CP violation in $D^0\to K^\pmπ^\mpπ^\pmπ^\mp$ decays is performed using data collected by the LHCb experiment in proton-proton collisions from 2015 to 2018, corresponding to an integrated luminosity of 6$\text{fb}^{-1}$. The ratio of promptly produced $D^0\to K^+π^- π^+π^-$ to $D^0\to K^-π^+ π^-π^+$ decay rates is measured as a function of $D^0$ decay time, both inclusive over phase space and in bins of phase space. Taking external inputs for the $D^0 -\overline{D}^0$ mixing parameters $x$ and $y$ allows constraints to be obtained on the hadronic parameters of the charm decay. When combined with previous measurements from charm-threshold experiments and at LHCb, improved knowledge is obtained for these parameters, which is valuable for studies of the angle $γ$ of the Unitarity Triangle. An alternative analysis is also performed, in which external inputs are taken for the hadronic parameters, and the mixing parameters are determined, including $Δx$ and $Δy$, which are nonzero in the presence of CP violation. It is found that $x=\left(0.85^{+0.15}_{-0.24}\right)\%$, $y=\left( 0.21^{+0.29}{-0.27} \right)\%$, $Δx=\left( -0.02\pm {0.04} \right)\% $ and $Δy=\left( 0.02^{+0.04}_{-0.03} \right)\%$. These results are consistent with previous measurements and the hypothesis of \CP conservation.
△ Less
Submitted 6 October, 2025;
originally announced October 2025.
-
Observation of a resonance-like structure near the $π^+π^-$ mass threshold in $ψ(3686) \rightarrow π^{+}π^{-}J/ψ$
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. B. Bertani,
D. Bettoni,
F. Bianchi,
E. Bianco,
A. Bortone,
I. Boyko,
R. A. Briere,
A. Brueggemann,
H. Cai
, et al. (677 additional authors not shown)
Abstract:
Based on the $(2712.4\pm14.4)\times 10^{6}$ $ψ(3686)$ events collected with the BESIII detector, we present a high-precision study of the $π^+π^-$ mass spectrum in $ψ(3686)\rightarrowπ^{+}π^{-}J/ψ$ decays. A clear resonance-like structure is observed near the $π^+π^-$ mass threshold for the first time. A fit with a Breit-Wigner function yields a mass of $285.6\pm 2.5~{\rm MeV}/c^2$ and a width of…
▽ More
Based on the $(2712.4\pm14.4)\times 10^{6}$ $ψ(3686)$ events collected with the BESIII detector, we present a high-precision study of the $π^+π^-$ mass spectrum in $ψ(3686)\rightarrowπ^{+}π^{-}J/ψ$ decays. A clear resonance-like structure is observed near the $π^+π^-$ mass threshold for the first time. A fit with a Breit-Wigner function yields a mass of $285.6\pm 2.5~{\rm MeV}/c^2$ and a width of $16.3\pm 0.9~{\rm MeV}$ with a statistical significance exceeding 10$σ$. To interpret the data, we incorporate final-state interactions (FSI) within two theoretical frameworks: chiral perturbation theory (ChPT) and QCD multipole expansion (QCDME). ChPT describes the spectrum above 0.3 GeV/$c^2$ but fails to reproduce the threshold enhancement. In contrast, the QCDME model, assuming the $ψ(3686)$ is an admixture of S- and D-wave charmonium, reproduces the data well. The pronounced dip near 0.3 GeV/$c^2$ offers new insight into the interplay between chiral dynamics and low-energy QCD.
△ Less
Submitted 28 September, 2025;
originally announced September 2025.
-
Search for the electromagnetic Dalitz decays $χ_{cJ}\to e^{+}e^{-}φ$
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. (697 additional authors not shown)
Abstract:
Using a data sample of $(2.712 \pm 0.014)\times10^{9}$ $ψ(3686)$ events collected at $\sqrt{s}=3.686$ GeV by the BESIII detector, we search for the rare electromagnetic Dalitz decays $χ_{cJ}\to e^+e^-φ~(J=0,\,1,\,2)$ via the radiative transitions $ψ(3686)\toγχ_{cJ}$. No statistically significant $χ_{cJ}\to e^+e^-φ$ signals are observed. The upper limits on the branching fractions of…
▽ More
Using a data sample of $(2.712 \pm 0.014)\times10^{9}$ $ψ(3686)$ events collected at $\sqrt{s}=3.686$ GeV by the BESIII detector, we search for the rare electromagnetic Dalitz decays $χ_{cJ}\to e^+e^-φ~(J=0,\,1,\,2)$ via the radiative transitions $ψ(3686)\toγχ_{cJ}$. No statistically significant $χ_{cJ}\to e^+e^-φ$ signals are observed. The upper limits on the branching fractions of $χ_{cJ}\to e^+e^-φ~(J=0,\,1,\,2)$, excluding the $φ$ resonance to $e^+e^-$ final states, are set to be $2.4\times10^{-7},~6.7\times10^{-7}$ and $4.1\times10^{-7}$ at 90\% confidence level, respectively. This is the first search for the electromagnetic Dalitz transition of P-wave charmonium $χ_{cJ}$ states to a light vector meson.
△ Less
Submitted 27 September, 2025;
originally announced September 2025.
-
Search for the lepton number violating decay $η\to π^+π^+e^-e^- + c.c.$ via $J/ψ\toφη$
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. (697 additional authors not shown)
Abstract:
Based on a sample of $ (10.087\pm 0.044)\times 10^{9} J/ψ$ events collected by the BESIII detector at the BEPCII collider, we perform the first search for the lepton number violating decay $η\to π^+π^+ e^-e^- + \text{c.c.}$ No signal is found, and an upper limit on the branching fraction of $η\to π^+π^+ e^-e^- + c.c.$ is set to be $4.6 \times 10^{-6}$ at the 90\% confidence level.
Based on a sample of $ (10.087\pm 0.044)\times 10^{9} J/ψ$ events collected by the BESIII detector at the BEPCII collider, we perform the first search for the lepton number violating decay $η\to π^+π^+ e^-e^- + \text{c.c.}$ No signal is found, and an upper limit on the branching fraction of $η\to π^+π^+ e^-e^- + c.c.$ is set to be $4.6 \times 10^{-6}$ at the 90\% confidence level.
△ Less
Submitted 26 September, 2025;
originally announced September 2025.
-
Measurement of the $W \to μν_μ$ cross-sections as a function of the muon transverse momentum in $pp$ collisions at 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,
R. Aleksiejunas,
F. Alessio,
P. Alvarez Cartelle,
R. Amalric,
S. Amato,
J. L. Amey,
Y. Amhis,
L. An
, et al. (1184 additional authors not shown)
Abstract:
The $pp \to W^{\pm} (\to μ^{\pm} ν_μ) X$ cross-sections are measured at a proton-proton centre-of-mass energy $\sqrt{s} = 5.02$ TeV using a dataset corresponding to an integrated luminosity of 100 pb$^{-1}$ recorded by the LHCb experiment. Considering muons in the pseudorapidity range $2.2 < η< 4.4$, the cross-sections are measured differentially in twelve intervals of muon transverse momentum bet…
▽ More
The $pp \to W^{\pm} (\to μ^{\pm} ν_μ) X$ cross-sections are measured at a proton-proton centre-of-mass energy $\sqrt{s} = 5.02$ TeV using a dataset corresponding to an integrated luminosity of 100 pb$^{-1}$ recorded by the LHCb experiment. Considering muons in the pseudorapidity range $2.2 < η< 4.4$, the cross-sections are measured differentially in twelve intervals of muon transverse momentum between $28 < p_\mathrm{T} < 52$ GeV. Integrated over $p_\mathrm{T}$, the measured cross-sections are \begin{align*} σ_{W^+ \to μ^+ ν_μ} &= 300.9 \pm 2.4 \pm 3.8 \pm 6.0~\text{pb}, \\ σ_{W^- \to μ^- \barν_μ} &= 236.9 \pm 2.1 \pm 2.7 \pm 4.7~\text{pb}, \end{align*} where the first uncertainties are statistical, the second are systematic, and the third are associated with the luminosity calibration. These integrated results are consistent with theoretical predictions.
This analysis introduces a new method to determine the $W$-boson mass using the measured differential cross-sections corrected for detector effects. The measurement is performed on this statistically limited dataset as a proof of principle and yields \begin{align*} m_W = 80369 \pm 130 \pm 33~\text{MeV}, \end{align*} where the first uncertainty is experimental and the second is theoretical.
△ Less
Submitted 23 September, 2025;
originally announced September 2025.
-
First evidence of $CP$ violation in beauty baryon to charmonium decays
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,
R. Aleksiejunas,
F. Alessio,
Z. Aliouche,
P. Alvarez Cartelle,
R. Amalric,
S. Amato,
J. L. Amey,
Y. Amhis
, et al. (1172 additional authors not shown)
Abstract:
A study of the difference in the $CP$ asymmetries between $Λ^0_b \rightarrow J / ψp π^-$ and $Λ^0_b \rightarrow J / ψp K^-$ decays, $Δ{\cal A}_{CP}$, is performed using proton-proton collision data collected by the LHCb experiment in the years 2015--2018, corresponding to an integrated luminosity of $6 {\rm fb}^{-1}$. This quantity is measured to be $ Δ{\cal A}_{CP}=(4.03\pm 1.18\pm 0.23)\%$, wher…
▽ More
A study of the difference in the $CP$ asymmetries between $Λ^0_b \rightarrow J / ψp π^-$ and $Λ^0_b \rightarrow J / ψp K^-$ decays, $Δ{\cal A}_{CP}$, is performed using proton-proton collision data collected by the LHCb experiment in the years 2015--2018, corresponding to an integrated luminosity of $6 {\rm fb}^{-1}$. This quantity is measured to be $ Δ{\cal A}_{CP}=(4.03\pm 1.18\pm 0.23)\%$, where the first uncertainty is statistical and the second is systematic. When combined with the previous LHCb result, a value of $Δ{\cal A}_{CP} = (4.31 \pm 1.06 \pm 0.28)\%$ is obtained, corresponding to a significance of $3.9σ$ against the $CP$ symmetry hypothesis. Studies of triple-product asymmetries, which provide an additional probe of $CP$ violation, show no significant deviation from $CP$ symmetry.
△ Less
Submitted 19 September, 2025;
originally announced September 2025.
-
Observation of $B_c^+ \to D h^+ h^-$ decays
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,
R. Aleksiejunas,
F. Alessio,
P. Alvarez Cartelle,
R. Amalric,
S. Amato,
J. L. Amey,
Y. Amhis,
L. An
, et al. (1184 additional authors not shown)
Abstract:
Searches are presented for $B_{c}^{+} \to D h^+ h^-$ decays, where $D$ is a charmed meson and $h^{\pm}$ is a charged pion or kaon, using $pp$ collision data collected by the LHCb experiment corresponding to an integrated luminosity of $9~\text{fb}^{-1}$. The decays $B_c^+\to D^+ K^+π^-$, $B_c^+\to D^{*+} K^+π^-$ and $B_c^+\to D_s^+ K^+ K^-$ are observed for the first time. Their branching fraction…
▽ More
Searches are presented for $B_{c}^{+} \to D h^+ h^-$ decays, where $D$ is a charmed meson and $h^{\pm}$ is a charged pion or kaon, using $pp$ collision data collected by the LHCb experiment corresponding to an integrated luminosity of $9~\text{fb}^{-1}$. The decays $B_c^+\to D^+ K^+π^-$, $B_c^+\to D^{*+} K^+π^-$ and $B_c^+\to D_s^+ K^+ K^-$ are observed for the first time. Their branching fractions, expressed as ratios relative to that of the $B_c^+\to B_s^0π^+$ decay, are determined to be \begin{align*} \mathcal{R}(B_c^+\to D^+ K^+π^-) =(1.96 \pm 0.23\pm 0.08 \pm 0.10)\times 10^{-3},&\\ \mathcal{R}(B_c^+\to D^{*+} K^+π^-) =(3.67 \pm 0.55 \pm 0.24\pm 0.20)\times 10^{-3},&\\ \mathcal{R}(B_c^+\to D_s^+ K^+ K^-) =(1.61 \pm 0.35\pm 0.13\pm 0.07)\times 10^{-3}, \end{align*} where the first uncertainty is statistical, the second is systematic, and the third is due to the limited precision on the $D$-meson branching fractions. The decay channels proceed primarily through excited $K^0$ or $D^0$ resonances or $φ$ mesons, and open a new avenue for studies of charge-parity violation in beauty mesons.
△ Less
Submitted 19 September, 2025;
originally announced September 2025.
-
First Observation of $Λ$ Hyperon Transverse Polarization in $ψ(3686)\toΛ\barΛ$
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. B. Bertani,
D. Bettoni,
F. Bianchi,
E. Bianco,
A. Bortone,
I. Boyko,
R. A. Briere,
A. Brueggemann,
H. Cai
, et al. (687 additional authors not shown)
Abstract:
Based on $(448.1\pm2.9)\times10^{6}$ $ψ(3686)$ events collected with the BESIII detector at the BEPCII collider, we present the first observation of spin transverse polarization of $Λ$ and $\barΛ$ hyperons produced coherently in the decay $ψ(3686)\toΛ(\to pπ^-)\barΛ(\to\bar pπ^+)$. The relative phase between the electric and magnetic hadronic form factors is measured to be…
▽ More
Based on $(448.1\pm2.9)\times10^{6}$ $ψ(3686)$ events collected with the BESIII detector at the BEPCII collider, we present the first observation of spin transverse polarization of $Λ$ and $\barΛ$ hyperons produced coherently in the decay $ψ(3686)\toΛ(\to pπ^-)\barΛ(\to\bar pπ^+)$. The relative phase between the electric and magnetic hadronic form factors is measured to be $ΔΦ=(21.0\pm3.7_{\rm stat.}\pm0.8_{\rm syst.})^{\circ}$. The angular distribution parameter $α_ψ=0.83\pm0.02_{\rm stat.}\pm0.01_{\rm syst.}$ is determined with a precision improved by a factor of 3.7 compared to the previous measurement. The relative phase between the $S$- and $D$-wave amplitudes for $Λ\barΛ$ is observed, and the effective interaction radius is determined to be $0.0450\pm0.0026_{\rm stat.}\pm0.0012_{\rm syst.}$ fm. These results provide new insights into the strong interaction mechanisms and the internal structure of baryons.
△ Less
Submitted 18 September, 2025;
originally announced September 2025.
-
A model-independent measurement of the CKM angle $γ$ in the decays $B^\pm\to[K^+K^-π^+π^-]_D h^\pm$ and $B^\pm\to[π^+π^-π^+π^-]_D h^\pm$ ($h = K, π$)
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,
R. Aleksiejunas,
F. Alessio,
Z. Aliouche,
P. Alvarez Cartelle,
R. Amalric,
S. Amato,
J. L. Amey,
Y. Amhis
, et al. (1163 additional authors not shown)
Abstract:
A model-independent determination of the CKM angle $γ$ is presented, using the $B^\pm\to[K^+K^-π^+π^-]_D h^\pm$ and $B^\pm\to[π^+π^-π^+π^-]_D h^\pm$ decays, with $h=K,π$. This measurement is the first phase-space-binned study of these decay modes, and uses a sample of proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of $9$fb$^{-1}$. The phase…
▽ More
A model-independent determination of the CKM angle $γ$ is presented, using the $B^\pm\to[K^+K^-π^+π^-]_D h^\pm$ and $B^\pm\to[π^+π^-π^+π^-]_D h^\pm$ decays, with $h=K,π$. This measurement is the first phase-space-binned study of these decay modes, and uses a sample of proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of $9$fb$^{-1}$. The phase-space bins are optimised for sensitivity to $γ$, and in each bin external inputs from the BESIII experiment are used to constrain the charm strong-phase parameters. The result of this binned analysis is $γ= (53.9_{-8.9}^{+9.5})^\circ$, where the uncertainty includes both statistical and systematic contributions. Furthermore, when combining with existing phase-space-integrated measurements of the same decay modes, a value of $γ= (52.6_{-6.4}^{+8.5})^\circ$ is obtained, which is one of the most precise determinations of $γ$ to date.
△ Less
Submitted 18 September, 2025;
originally announced September 2025.
-
Measurement of the branching fraction of the $Λ_b^0\to J/ψΛ$ decay and isospin asymmetry of $B\to J/ψK$ decays
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,
M. Akthar,
P. Albicocco,
J. Albrecht,
R. Aleksiejunas,
F. Alessio,
P. Alvarez Cartelle,
R. Amalric,
S. Amato,
J. L. Amey,
Y. Amhis
, et al. (1191 additional authors not shown)
Abstract:
This paper describes a measurement of the $Λ_b^0\to J/ψΛ$ branching fraction using data collected with the LHCb experiment in proton-proton collisions from 2016 to 2018. The dataset corresponds to an integrated luminosity of 5.4$\,\text{fb}^{-1}$. The branching fraction is determined relative to that of $B^0\to J/ψK^0_\text{S}$ decays,…
▽ More
This paper describes a measurement of the $Λ_b^0\to J/ψΛ$ branching fraction using data collected with the LHCb experiment in proton-proton collisions from 2016 to 2018. The dataset corresponds to an integrated luminosity of 5.4$\,\text{fb}^{-1}$. The branching fraction is determined relative to that of $B^0\to J/ψK^0_\text{S}$ decays, $\frac{\mathcal{B}(Λ_b^0\to J/ψΛ)}{\mathcal{B}(B^0\to J/ψK^0_\text{S}} = 0.750 \pm 0.005 \pm 0.022 \pm 0.005 \pm 0.062\,,$ yielding $\mathcal{B}(Λ_b^0\to J/ψΛ) = (3.34 \pm 0.02 \pm 0.10 \pm 0.08 \pm 0.28)\times 10^{-4}$, where the first uncertainty is statistical, the second systematic, the third due to external inputs on branching fractions and the fourth due to the ratio of $Λ_b^0$ baryon and $B^0$ meson hadronisation fractions. In addition, the isospin asymmetry between the rates of $B^0\to J/ψK^0_\text{S}$ and $B^+\to J/ψK^+$ decays is measured to be $A_{\rm I} = -0.0135 \pm 0.0004 \pm 0.0133$, where the first uncertainty is statistical and the second systematic.
△ Less
Submitted 22 September, 2025; v1 submitted 16 September, 2025;
originally announced September 2025.
-
Determination of CKM matrix element and axial vector form factors from weak decays of quantum-entangled strange baryons
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. (705 additional authors not shown)
Abstract:
The electromagnetic structure of the nucleon can be determined from the scattering of electrons off a nucleon target. However, to study its axial structure, neutrino beams are required. The results from these experiments should be extrapolated to zero energy-momentum transfers to access the static properties of the nucleon. For baryons with strange quarks, hyperons, the static limit can instead be…
▽ More
The electromagnetic structure of the nucleon can be determined from the scattering of electrons off a nucleon target. However, to study its axial structure, neutrino beams are required. The results from these experiments should be extrapolated to zero energy-momentum transfers to access the static properties of the nucleon. For baryons with strange quarks, hyperons, the static limit can instead be approached in semi-leptonic decays, which give direct access to the weak magnetism and axial-vector coupling strengths that are inaccessible in electromagnetic interactions. The axial-vector coupling as while weak magnetism coupling and the overall normalization, given by form factor $f_1$, are being determined with increased precision from the theory of strong interactions using a first principles formulation on the space--time lattice. Furthermore, the probability of the semi-leptonic hyperon decay is approximately proportional to $|V_{us}|^2\cdot (f_1^2+3g_1^2)$, where $V_{us}$ is the CKM matrix element responsible for the transition between an $s$ and a $u$ quark. Current determinations of $|V_{us}|$ come from kaon decays, but the results are not consistent and could indicate a deviation from CKM matrix unitarity, a tell-tale sign of physics beyond the Standard Model (SM) of elementary particles. Here we determine the absolute branching fraction and weak coupling strengths for $Λ\to p e^-\barν_e$, and $\bar Λ\to \bar p e^+ν_e$. These observables combined with form factors determined from first-principle lattice QCD calculations allow for the extraction of the $|V_{us}|$ value. We demonstrate how $|V_{us}|$ can be extracted with increasing sensitivity using polarized hyperons from entangled, baryon-antibaryon pairs, thus enabling a complementary road to that of meson decays. In addition, the presented experimental method can be used for other semileptonic decays of baryons.
△ Less
Submitted 12 September, 2025; v1 submitted 11 September, 2025;
originally announced September 2025.