Showing 1–38 of 38 results for author: Somov, A

Long Range Outlook for Short-Range Correlations

Authors: Nadia Fomin, Or Hen, Julian Kahlbow, Dien Nguyen, Jackson Pybus, Noemi Rocco, Misak Sargsian, Sandra Nathaly Santiesteban, Ronen Weiss, Douglas W. Higinbotham, Lawrence Weinstein, Devi Adhikari, Hisham Albataineh, Massimiliano Alvioli, Lorenzo Andreoli, John Arrington, Carlos Ayerbe Gayoso, A. B. Balantekin, Carlos Bertulani, Hem Bhatt, Sudip Bhattarai, William J. Briscoe, Sayak Chatterjee, Hector Chinchay, E. O. Cohn , et al. (77 additional authors not shown)

Abstract: Short range correlated (SRC) N N pairs are pairs of nucleons with high relative momentum (prel > kF where kF ~ 250 MeV/c is the Fermi momentum in medium to heavy nuclei) and lower center of mass momentum. The motivation for studying SRC pairs ranges from a desire to achieve a more comprehensive understanding of the many-body nuclear wave-function at high-resolution to searching for explicit QCD-dy… ▽ More Short range correlated (SRC) N N pairs are pairs of nucleons with high relative momentum (prel > kF where kF ~ 250 MeV/c is the Fermi momentum in medium to heavy nuclei) and lower center of mass momentum. The motivation for studying SRC pairs ranges from a desire to achieve a more comprehensive understanding of the many-body nuclear wave-function at high-resolution to searching for explicit QCD-dynamics effects within the nuclear medium, not to mention connections to many other open problems in nuclear physics. Exploring short-range correlations was one of the physics motivations for building CEBAF (now Jefferson Lab). Scientists used the high luminosity and high energy of this cutting-edge machine to find kinematics that cleanly showed the signals of short-range correlations. This paved the way in the last two decades for tremendous progress understanding these correlations. This paper reviews recent progress and highlights outstanding questions and areas that need further study. △ Less

Submitted 14 January, 2026; originally announced January 2026.

$J/ψ$-Meson Nucleon Scattering Length from Threshold Photoproduction on Light Nuclei

Authors: Igor I. Strakovsky, William J. Briscoe, Philipp Gubler, Jackson R. Pybus, Axel Schmidt, Alexander Somov

Abstract: The quality of recent SRC/CT Collaboration $J/ψ$ photoproduction data off a $^4$He target from Hall~D at Jefferson Laboratory, combined with the feasibility of measuring the reaction close to the free-nucleon energy threshold, opens the door to using incoherent $J/ψ$ photoproduction to access a variety of interesting physics aspects. An example is an estimate of the $J/ψ~p$ scattering length… ▽ More The quality of recent SRC/CT Collaboration $J/ψ$ photoproduction data off a $^4$He target from Hall~D at Jefferson Laboratory, combined with the feasibility of measuring the reaction close to the free-nucleon energy threshold, opens the door to using incoherent $J/ψ$ photoproduction to access a variety of interesting physics aspects. An example is an estimate of the $J/ψ~p$ scattering length $|α_{J/ψ~p}|$ on the bound proton obtained using the Vector Meson Dominance model. This value can be compared with that of the free proton from the GlueX Collaboration. One may then project what would be expected from the SRC/CT Collaboration Experiment E12--25--002, which was recently approved by the JLab PAC. Using a plane-wave theoretical model to generate quasi-data, we find the experiment could achieve a result of $|α_{J/ψ~p}| = 3.08\pm 0.45~\mathrm{mfm}$, an uncertainty competitive with that of the free-proton measurement. A comparison between the two would allow an evaluation of the effects of medium modification in the case of light nuclei. △ Less

Submitted 9 December, 2025; originally announced December 2025.

Comments: 7 pages, 2 figures, 2 tables

Baryon-antibaryon photoproduction cross sections off the proton

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

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

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

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

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

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

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

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

Submitted 24 October, 2025; originally announced October 2025.

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

The beam test facility at Jefferson Lab for the precise energy measurement of future calorimeter concepts

Authors: Vladimir V. Berdnikov, Alexander Somov

Abstract: In experimental nuclear physics (NP), high-precision electromagnetic calorimetry typically requires a good energy resolution and linear photosensor response on the level of (1-2)% over a full dynamic range of the detector. The beam of secondary leptons at the Jefferson Lab experimental complex, provided by the Hall D pair spectrometer (PS), is an optimal facility for studies aiming to understand t… ▽ More In experimental nuclear physics (NP), high-precision electromagnetic calorimetry typically requires a good energy resolution and linear photosensor response on the level of (1-2)% over a full dynamic range of the detector. The beam of secondary leptons at the Jefferson Lab experimental complex, provided by the Hall D pair spectrometer (PS), is an optimal facility for studies aiming to understand the impact of light collection and signal processing on calorimetry energy resolution under real experimental conditions. The light emission and collection processes depend on radiator component quality and type, while signal processing depends on photosensor type and front-end electronics design. Various calorimeter tower components and detector assemblies for current and future NP experiments were tested within the lepton momentum range of (3-6) GeV/c using PS. The energy resolution of the PS itself is estimated to be better than approximately 0.6%. △ Less

Submitted 3 October, 2025; originally announced October 2025.

Journal ref: Proceedings Volume 13621, Hard X-Ray, Gamma-Ray, and Neutron Detector Physics XXVII; 1362109 (2025)

Lead tungstate calorimeter of the Jefferson Lab Eta Factory experiment

Authors: Alexander Somov

Abstract: A new electromagnetic calorimeter (ECAL) consisting of 1596 lead tungstate PbWO$_{\rm 4}$ scintillating crystals has been fabricated and installed in the experimental Hall D at Jefferson Lab (JLab). The high-granularity, high-resolution calorimeter is required by the JLab Eta Factory experiment, whose main physics goal is to study rare decays of eta mesons. The ECAL replaced the inner part of the… ▽ More A new electromagnetic calorimeter (ECAL) consisting of 1596 lead tungstate PbWO$_{\rm 4}$ scintillating crystals has been fabricated and installed in the experimental Hall D at Jefferson Lab (JLab). The high-granularity, high-resolution calorimeter is required by the JLab Eta Factory experiment, whose main physics goal is to study rare decays of eta mesons. The ECAL replaced the inner part of the forward lead glass calorimeter of the GlueX detector. Signals from the detector will be digitized using twelve-bit flash analog-to-digital converters operated at a sampling rate of 250 MHz. The ECAL is integrated into the trigger system of the GlueX detector using electronics modules designed at JLab. The ECAL is currently at the commissioning stage and should be ready for the physics run in January 2025. We will give an overview of the JEF experiment, the design and construction of the ECAL, and the integration of the detector and its infrastructure into the Hall D experimental setup. △ Less

Submitted 6 October, 2025; originally announced October 2025.

Comments: 4 pages, 9 figures, contribution to the 20th International Conference on Calorimetry in Particle Physics (CALOR2024)

Journal ref: EPJ Web Conf., 320, 00058 (2025)

Status of the PrimEx $η$ experiment at Jefferson Lab

Authors: Alexander Somov

Abstract: The GlueX detector in the experimental Hall $D$ at Jefferson Lab offers a unique opportunity to perform a measurement of the decay width of eta mesons through the Primakoff effect. The PrimEx $η$ experiment complements the physics program at Jefferson Lab on measuring the decay width of light pseudoscalar mesons via the Primakoff process. The goal of PrimEx $η$ is to measure differential cross sec… ▽ More The GlueX detector in the experimental Hall $D$ at Jefferson Lab offers a unique opportunity to perform a measurement of the decay width of eta mesons through the Primakoff effect. The PrimEx $η$ experiment complements the physics program at Jefferson Lab on measuring the decay width of light pseudoscalar mesons via the Primakoff process. The goal of PrimEx $η$ is to measure differential cross sections of $η$ mesons at forward angles using a beam of tagged photons incident on a liquid ${}^{4}{\rm He}$ target. The data will be used for the extraction of the decay width. This measurement is vital for understanding fundamental properties like the ratios of the light quark masses and the $η$-$η^\prime$ mixing angle, and will provide an important test of chiral symmetry breaking in QCD. Our experimental results will help reduce uncertainties on partial widths of all other $η$ decays. The experiment collected data during three physics runs between 2019 and 2022. We will give an overview of the PrimEx $η$ experiment and the current status of our data analyses. We will also discuss the feasibility of conducting future Primakoff measurements in light of the recent upgrade of the GlueX forward calorimeter and the potential accelerator energy upgrade to 22 GeV. △ Less

Submitted 5 October, 2025; originally announced October 2025.

Comments: 15 pages, 15 figures; contribution to the 11th International Workshop on Chiral Dynamics (CD2024). To be published in PoS, volume 479. as (CD2024)073

Installation and first commissioning results of the JEF lead tungstate calorimeter

Authors: Alexander Somov, Vladimir Berdnikov

Abstract: The Electromagnetic Calorimeter (ECAL), consisting of 1,596 lead tungstate scintillating crystals, has been recently constructed and installed in Experimental Hall D at Jefferson Lab (JLab). The calorimeter is a key component of the JLab Eta Factory Experiment, whose main goal is to measure the decays of eta and eta prime mesons into multi-photon final states. The ECAL replaces the inner part of t… ▽ More The Electromagnetic Calorimeter (ECAL), consisting of 1,596 lead tungstate scintillating crystals, has been recently constructed and installed in Experimental Hall D at Jefferson Lab (JLab). The calorimeter is a key component of the JLab Eta Factory Experiment, whose main goal is to measure the decays of eta and eta prime mesons into multi-photon final states. The ECAL replaces the inner part of the former forward lead-glass calorimeter. Scintillation light from each crystal is detected using Hamamatsu R4125 photomultiplier tubes. Calorimeter modules were fabricated and tested in the lab using light from light-emitting diodes before being installed in the detector frame. The detector is currently undergoing commissioning using the light monitoring system and cosmic rays. We will present an overview of the fabrication and testing of the calorimete modules, along with the first detector commissioning results. The ECAL was ready for data-taking in spring 2025. △ Less

Submitted 3 October, 2025; originally announced October 2025.

Journal ref: Proceedings Volume 13621, Hard X-Ray, Gamma-Ray, and Neutron Detector Physics XXVII; 136210C (2025)

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

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

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

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

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

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

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

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

Submitted 6 January, 2025; originally announced January 2025.

Comments: 8 pages, 4 figures plus supplemental material

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

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

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

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

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

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

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

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

Comments: 7 pages, 3 figures plus supplemental materials

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

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

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

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

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

Search for axion-like particles through nuclear Primakoff production using the GlueX detector

Authors: J. R. Pybus, T. Kolar, B. Devkota, P. Sharp, B. Yu, O. Hen, E. Piasetzky, S. N. Santiesteban, A. Schmidt, A. Somov, Y. Soreq, H. Szumila-Vance, C. S. Akondi, C. Ayerbe Gayoso, V. V. Berdnikov, H. Bhatt, D. Bhetuwal, M. M. Dalton, A. Deur, R. Dotel, C. Fanelli, J. Guo, T. J. Hague, D. W. Higinbotham, N. D. Hoffman , et al. (18 additional authors not shown)

Abstract: We report on the results of the first search for the production of axion-like particles (ALP) via Primakoff production on nuclear targets using the GlueX detector. This search uses an integrated luminosity of 100 pb$^{-1}\cdot$nucleon on a $^{12}$C target, and explores the mass region of 200 < $m_a$ < 450 MeV via the decay $X\rightarrowγγ$. This mass range is between the $π^0$ and $η$ masses, whic… ▽ More We report on the results of the first search for the production of axion-like particles (ALP) via Primakoff production on nuclear targets using the GlueX detector. This search uses an integrated luminosity of 100 pb$^{-1}\cdot$nucleon on a $^{12}$C target, and explores the mass region of 200 < $m_a$ < 450 MeV via the decay $X\rightarrowγγ$. This mass range is between the $π^0$ and $η$ masses, which enables the use of the measured $η$ production rate to obtain absolute bounds on the ALP production with reduced sensitivity to experimental luminosity and detection efficiency. We find no evidence for an ALP, consistent with previous searches in the quoted mass range, and present limits on the coupling on the scale of $O$(1 TeV). We further find that the ALP production limit we obtain is hindered by the peaking structure of the non-target-related dominant background in GlueX, which we treat by using data on $^4$He to estimate and subtract these backgrounds. We comment on how this search can be improved in a future higher-statistics dedicated measurement. △ Less

Submitted 11 August, 2023; originally announced August 2023.

Strong Interaction Physics at the Luminosity Frontier with 22 GeV Electrons at Jefferson Lab

Authors: A. Accardi, P. Achenbach, D. Adhikari, A. Afanasev, C. S. Akondi, N. Akopov, M. Albaladejo, H. Albataineh, M. Albrecht, B. Almeida-Zamora, M. Amaryan, D. Androić, W. Armstrong, D. S. Armstrong, M. Arratia, J. Arrington, A. Asaturyan, A. Austregesilo, H. Avagyan, T. Averett, C. Ayerbe Gayoso, A. Bacchetta, A. B. Balantekin, N. Baltzell, L. Barion , et al. (419 additional authors not shown)

Abstract: This document presents the initial scientific case for upgrading the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab (JLab) to 22 GeV. It is the result of a community effort, incorporating insights from a series of workshops conducted between March 2022 and April 2023. With a track record of over 25 years in delivering the world's most intense and precise multi-GeV electron… ▽ More This document presents the initial scientific case for upgrading the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab (JLab) to 22 GeV. It is the result of a community effort, incorporating insights from a series of workshops conducted between March 2022 and April 2023. With a track record of over 25 years in delivering the world's most intense and precise multi-GeV electron beams, CEBAF's potential for a higher energy upgrade presents a unique opportunity for an innovative nuclear physics program, which seamlessly integrates a rich historical background with a promising future. The proposed physics program encompass a diverse range of investigations centered around the nonperturbative dynamics inherent in hadron structure and the exploration of strongly interacting systems. It builds upon the exceptional capabilities of CEBAF in high-luminosity operations, the availability of existing or planned Hall equipment, and recent advancements in accelerator technology. The proposed program cover various scientific topics, including Hadron Spectroscopy, Partonic Structure and Spin, Hadronization and Transverse Momentum, Spatial Structure, Mechanical Properties, Form Factors and Emergent Hadron Mass, Hadron-Quark Transition, and Nuclear Dynamics at Extreme Conditions, as well as QCD Confinement and Fundamental Symmetries. Each topic highlights the key measurements achievable at a 22 GeV CEBAF accelerator. Furthermore, this document outlines the significant physics outcomes and unique aspects of these programs that distinguish them from other existing or planned facilities. In summary, this document provides an exciting rationale for the energy upgrade of CEBAF to 22 GeV, outlining the transformative scientific potential that lies within reach, and the remarkable opportunities it offers for advancing our understanding of hadron physics and related fundamental phenomena. △ Less

Submitted 24 August, 2023; v1 submitted 13 June, 2023; originally announced June 2023.

Comments: Updates to the list of authors; Preprint number changed from theory to experiment; Updates to sections 4 and 6, including additional figures

Report number: JLAB-PHY-23-3840

Measurement of Spin-Density Matrix Elements in $ρ(770)$ Production with a Linearly Polarized Photon Beam at $E_γ= 8.2\,-\,8.8\,\text{GeV}$

Authors: GlueX Collaboration, S. Adhikari, F. Afzal, C. S. Akondi, M. Albrecht, M. Amaryan, V. Arroyave, A. Asaturyan, A. Austregesilo, Z. Baldwin, F. Barbosa, J. Barlow, E. Barriga, R. Barsotti, T. D. Beattie, V. V. Berdnikov, T. Black, W. Boeglin, W. J. Briscoe, T. Britton, W. K. Brooks, D. Byer, E. Chudakov, P. L. Cole, O. Cortes , et al. (128 additional authors not shown)

Abstract: The GlueX experiment at Jefferson Lab studies photoproduction of mesons using linearly polarized $8.5\,\text{GeV}$ photons impinging on a hydrogen target which is contained within a detector with near-complete coverage for charged and neutral particles. We present measurements of spin-density matrix elements for the photoproduction of the vector meson $ρ$(770). The statistical precision achieved e… ▽ More The GlueX experiment at Jefferson Lab studies photoproduction of mesons using linearly polarized $8.5\,\text{GeV}$ photons impinging on a hydrogen target which is contained within a detector with near-complete coverage for charged and neutral particles. We present measurements of spin-density matrix elements for the photoproduction of the vector meson $ρ$(770). The statistical precision achieved exceeds that of previous experiments for polarized photoproduction in this energy range by orders of magnitude. We confirm a high degree of $s$-channel helicity conservation at small squared four-momentum transfer $t$ and are able to extract the $t$-dependence of natural and unnatural-parity exchange contributions to the production process in detail. We confirm the dominance of natural-parity exchange over the full $t$ range. We also find that helicity amplitudes in which the helicity of the incident photon and the photoproduced $ρ(770)$ differ by two units are negligible for $-t<0.5\,\text{GeV}^{2}/c^{2}$. △ Less

Submitted 9 July, 2024; v1 submitted 15 May, 2023; originally announced May 2023.

Comments: 15 pages, 11 figures

Journal ref: Phys. Rev. C 108, 055204 (2023)

Measurement of the J/$ψ$ photoproduction cross section over the full near-threshold kinematic region

Authors: GlueX Collaboration, S. Adhikari, F. Afzal, C. S. Akondi, M. Albrecht, M. Amaryan, V. Arroyave, A. Asaturyan, A. Austregesilo, Z. Baldwin, F. Barbosa, J. Barlow, E. Barriga, R. Barsotti, T. D. Beattie, V. V. Berdnikov, T. Black, W. Boeglin, W. J. Briscoe, T. Britton, W. K. Brooks, D. Byer, E. Chudakov, P. L. Cole, O. Cortes , et al. (128 additional authors not shown)

Abstract: We report the total and differential cross sections for $J/ψ$ photoproduction with the large acceptance GlueX spectrometer for photon beam energies from the threshold at 8.2~GeV up to 11.44~GeV and over the full kinematic range of momentum transfer squared, $t$. Such coverage facilitates the extrapolation of the differential cross sections to the forward ($t = 0$) point beyond the physical region.… ▽ More We report the total and differential cross sections for $J/ψ$ photoproduction with the large acceptance GlueX spectrometer for photon beam energies from the threshold at 8.2~GeV up to 11.44~GeV and over the full kinematic range of momentum transfer squared, $t$. Such coverage facilitates the extrapolation of the differential cross sections to the forward ($t = 0$) point beyond the physical region. The forward cross section is used by many theoretical models and plays an important role in understanding $J/ψ$ photoproduction and its relation to the $J/ψ-$proton interaction. These measurements of $J/ψ$ photoproduction near threshold are also crucial inputs to theoretical models that are used to study important aspects of the gluon structure of the proton, such as the gluon Generalized Parton Distribution (GPD) of the proton, the mass radius of the proton, and the trace anomaly contribution to the proton mass. We observe possible structures in the total cross section energy dependence and find evidence for contributions beyond gluon exchange in the differential cross section close to threshold, both of which are consistent with contributions from open-charm intermediate states. △ Less

Submitted 9 July, 2024; v1 submitted 7 April, 2023; originally announced April 2023.

Comments: 15 pages 18 figures

Search for photoproduction of axion-like particles at GlueX

Authors: GlueX Collaboration, S. Adhikari, C. S. Akondi, M. Albrecht, A. Ali, M. Amaryan, A. Asaturyan, A. Austregesilo, Z. Baldwin, F. Barbosa, J. Barlow, E. Barriga, R. Barsotti, T. D. Beattie, V. V. Berdnikov, T. Black, W. Boeglin, W. J. Briscoe, T. Britton, W. K. Brooks, E. Chudakov, S. Cole, P. L. Cole, O. Cortes, V. Crede , et al. (120 additional authors not shown)

Abstract: We present a search for axion-like particles, $a$, produced in photon-proton collisions at a center-of-mass energy of approximately 4 GeV, focusing on the scenario where the $a$-gluon coupling is dominant. The search uses $a\toγγ$ and $a\toπ^+π^-π^0$ decays, and a data sample corresponding to an integrated luminosity of 168 pb$^{-1}$ collected with the GlueX detector. The search for $a\toγγ$ decay… ▽ More We present a search for axion-like particles, $a$, produced in photon-proton collisions at a center-of-mass energy of approximately 4 GeV, focusing on the scenario where the $a$-gluon coupling is dominant. The search uses $a\toγγ$ and $a\toπ^+π^-π^0$ decays, and a data sample corresponding to an integrated luminosity of 168 pb$^{-1}$ collected with the GlueX detector. The search for $a\toγγ$ decays is performed in the mass range of $180 < m_a < 480$ MeV, while the search for $a\toπ^+π^-π^0$ decays explores the $600 < m_a < 720$ MeV region. No evidence for a signal is found, and 90% confidence-level exclusion limits are placed on the $a$-gluon coupling strength. These constraints are the most stringent to date over much of the mass ranges considered. △ Less

Submitted 24 March, 2022; v1 submitted 27 September, 2021; originally announced September 2021.

Comments: 8 pages, 4 figures, 2 tables; updated to published version

Report number: GlueX Doc 4971

Journal ref: Phys. Rev. D 105, 052007 (2022)

Measurement of Spin Density Matrix Elements in $Λ(1520)$ Photoproduction at 8.2-8.8 GeV

Authors: GlueX Collaboration, S. Adhikari, C. S. Akondi, M. Albrecht, A. Ali, M. Amaryan, A. Asaturyan, A. Austregesilo, Z. Baldwin, F. Barbosa, J. Barlow, E. Barriga, R. Barsotti, T. D. Beattie, V. V. Berdnikov, T. Black, W. Boeglin, W. J. Briscoe, T. Britton, W. K. Brooks, E. Chudakov, S. Cole, P. L. Cole, O. Cortes, V. Crede , et al. (121 additional authors not shown)

Abstract: We report on the measurement of spin density matrix elements of the $Λ(1520)$ in the photoproduction reaction $γp\rightarrow Λ(1520)K^+$, via its subsequent decay to $K^{-}p$. The measurement was performed as part of the GlueX experimental program in Hall D at Jefferson Lab using a linearly polarized photon beam with $E_γ=$ 8.2-8.8 GeV. These are the first such measurements in this photon energy r… ▽ More We report on the measurement of spin density matrix elements of the $Λ(1520)$ in the photoproduction reaction $γp\rightarrow Λ(1520)K^+$, via its subsequent decay to $K^{-}p$. The measurement was performed as part of the GlueX experimental program in Hall D at Jefferson Lab using a linearly polarized photon beam with $E_γ=$ 8.2-8.8 GeV. These are the first such measurements in this photon energy range. Results are presented in bins of momentum transfer squared, $-(t-t_\text{0})$. We compare the results with a Reggeon exchange model and determine that natural exchange amplitudes are dominant in $Λ(1520)$ photoproduction. △ Less

Submitted 3 March, 2022; v1 submitted 26 July, 2021; originally announced July 2021.

Comments: 11 pages, 8 figures, accepted version

Report number: GlueX-Doc 4258

Journal ref: Phys. Rev. C 105, 035201 (2022)

Deeply virtual Compton scattering using a positron beam in Hall-C at Jefferson Lab

Authors: A. Afanasev, I. Albayrak, S. Ali, M. Amaryan, J. R. M. Annand, A. Asaturyan, V. Bellini, V. V. Berdnikov, M. Boer, K. Brinkmann, W. J. Briscoe, A. Camsonne, M. Caudron, L. Causse, M. Carmignotto, D. Day, M. Defurne, S. Diehl, R. Ent, P. Chatagnon, R. Dupré, D. Dutta, M. Ehrhart, M. A. I. Fernando, T. Forest , et al. (49 additional authors not shown)

Abstract: We propose to use the High Momentum Spectrometer of Hall C combined with the Neutral Particle Spectrometer (NPS) to perform high precision measurements of the Deeply Virtual Compton Scattering (DVCS) cross section using a beam of positrons. The combination of measurements with oppositely charged incident beams is the only unambiguous way to disentangle the contribution of the DVCS$^2$ term in the… ▽ More We propose to use the High Momentum Spectrometer of Hall C combined with the Neutral Particle Spectrometer (NPS) to perform high precision measurements of the Deeply Virtual Compton Scattering (DVCS) cross section using a beam of positrons. The combination of measurements with oppositely charged incident beams is the only unambiguous way to disentangle the contribution of the DVCS$^2$ term in the photon electroproduction cross section from its interference with the Bethe-Heitler amplitude. This provides a stronger way to constrain the Generalized Parton Distributions of the nucleon. A wide range of kinematics accessible with an 11 GeV beam off an unpolarized proton target will be covered. The $Q^2-$dependence of each contribution will be measured independently. △ Less

Submitted 22 January, 2022; v1 submitted 13 May, 2021; originally announced May 2021.

Studying Short-Range Correlations with Real Photon Beams at GlueX

Authors: O. Hen, M. Patsyuk, E. Piasetzky, A. Schmidt, A. Somov, H. Szumila-Vance, L. B. Weinstein, D. Dutta, H. Gao, M. Amaryan, A. Ashkenazi, A. Beck, V. Berdnikov, T. Black, W. J. Briscoe, T. Britton, W. Brooks, R. Cruz-Torres, M. M. Dalton, A. Denniston, A. Deur, H. Egiyan, C. Fanelli, S. Fegan, S. Furletov , et al. (37 additional authors not shown)

Abstract: The past few years has seen tremendous progress in our understanding of short-range correlated (SRC) pairing of nucleons within nuclei, much of it coming from electron scattering experiments leading to the break-up of an SRC pair. The interpretation of these experiments rests on assumptions about the mechanism of the reaction. These assumptions can be directly tested by studying SRC pairs using al… ▽ More The past few years has seen tremendous progress in our understanding of short-range correlated (SRC) pairing of nucleons within nuclei, much of it coming from electron scattering experiments leading to the break-up of an SRC pair. The interpretation of these experiments rests on assumptions about the mechanism of the reaction. These assumptions can be directly tested by studying SRC pairs using alternate probes, such as real photons. We propose a 30-day experiment using the Hall D photon beam, nuclear targets, and the GlueX detector in its standard configuration to study short-range correlations with photon-induced reactions. Several different reaction channels are possible, and we project sensitivity in most channels to equal or exceed the 6 GeV-era SRC experiments from Halls A and B. The proposed experiment will therefore decisively test the phenomena of np dominance, the short-distance NN interaction, and reaction theory, while also providing new insight into bound nucleon structure and the onset of color transparency. △ Less

Submitted 3 October, 2020; v1 submitted 21 September, 2020; originally announced September 2020.

Comments: 38 pages, 26 figures, proposal for Jefferson Lab Experiment E12-19-003, submitted to Jefferson Lab PAC 47 (2019)

Measurement of beam asymmetry for $π^-Δ^{++}$ photoproduction on the proton at $E_γ$=8.5 GeV

Authors: GlueX Collaboration, S. Adhikari, C. S. Akondi, A. Ali, M. Amaryan, A. Asaturyan, A. Austregesilo, Z. Baldwin, F. Barbosa, J. Barlow, E. Barriga, R. Barsotti, T. D. Beattie, V. V. Berdnikov, T. Black, W. Boeglin, W. J. Briscoe, T. Britton, W. K. Brooks, B. E. Cannon, E. Chudakov, S. Cole, O. Cortes, V. Crede, M. M. Dalton , et al. (112 additional authors not shown)

Abstract: We report a measurement of the $π^-$ photoproduction beam asymmetry for the reaction $\vecγ p \rightarrow π^- Δ^{++}$ using data from the GlueX experiment in the photon beam energy range 8.2--8.8 GeV. The asymmetry $Σ$ is measured as a function of four-momentum transfer $t$ to the $Δ^{++}$ and compared to phenomenological models. We find that $Σ$ varies as a function of $t$: negative at smaller va… ▽ More We report a measurement of the $π^-$ photoproduction beam asymmetry for the reaction $\vecγ p \rightarrow π^- Δ^{++}$ using data from the GlueX experiment in the photon beam energy range 8.2--8.8 GeV. The asymmetry $Σ$ is measured as a function of four-momentum transfer $t$ to the $Δ^{++}$ and compared to phenomenological models. We find that $Σ$ varies as a function of $t$: negative at smaller values and positive at higher values of $|t|$. The reaction can be described theoretically by $t$-channel particle exchange requiring pseudoscalar, vector, and tensor intermediaries. In particular, this reaction requires charge exchange, allowing us to probe pion exchange and the significance of higher-order corrections to one-pion exchange at low momentum transfer. Constraining production mechanisms of conventional mesons may aid in the search for and study of unconventional mesons. This is the first measurement of the process at this energy. △ Less

Submitted 8 January, 2021; v1 submitted 15 September, 2020; originally announced September 2020.

Comments: 7 pages, 5 figures

Report number: GlueX-Doc 4272

Journal ref: Phys. Rev. C 103, 022201 (2021)

Strange Hadron Spectroscopy with Secondary KL Beam in Hall D

Authors: KLF Collaboration, Moskov Amaryan, Mikhail Bashkanov, Sean Dobbs, James Ritman, Justin Stevens, Igor Strakovsky, Shankar Adhikari, Arshak Asaturyan, Alexander Austregesilo, Marouen Baalouch, Vitaly Baturin, Vladimir Berdnikov, Olga Cortes Becerra, Timothy Black, Werner Boeglin, William Briscoe, William Brooks, Volker Burkert, Eugene Chudakov, Geraint Clash, Philip Cole, Volker Crede, Donal Day, Pavel Degtyarenko , et al. (128 additional authors not shown)

Abstract: We propose to create a secondary beam of neutral kaons in Hall D at Jefferson Lab to be used with the GlueX experimental setup for strange hadron spectroscopy. The superior CEBAF electron beam will enable a flux on the order of $1\times 10^4~K_L/sec$, which exceeds the flux of that previously attained at SLAC by three orders of magnitude. The use of a deuteron target will provide first measurement… ▽ More We propose to create a secondary beam of neutral kaons in Hall D at Jefferson Lab to be used with the GlueX experimental setup for strange hadron spectroscopy. The superior CEBAF electron beam will enable a flux on the order of $1\times 10^4~K_L/sec$, which exceeds the flux of that previously attained at SLAC by three orders of magnitude. The use of a deuteron target will provide first measurements ever with neutral kaons on neutrons. The experiment will measure both differential cross sections and self-analyzed polarizations of the produced $Λ$, $Σ$, $Ξ$, and $Ω$ hyperons using the GlueX detector at the Jefferson Lab Hall D. The measurements will span CM $\cosθ$ from $-0.95$ to 0.95 in the range W = 1490 MeV to 2500 MeV. The new data will significantly constrain the partial wave analyses and reduce model-dependent uncertainties in the extraction of the properties and pole positions of the strange hyperon resonances, and establish the orbitally excited multiplets in the spectra of the $Ξ$ and $Ω$ hyperons. Comparison with the corresponding multiplets in the spectra of the charm and bottom hyperons will provide insight into he accuracy of QCD-based calculations over a large range of masses. The proposed facility will have a defining impact in the strange meson sector through measurements of the final state $Kπ$ system up to 2 GeV invariant mass. This will allow the determination of pole positions and widths of all relevant $K^\ast(Kπ)$ $S$-,$P$-,$D$-,$F$-, and $G$-wave resonances, settle the question of the existence or nonexistence of scalar meson $κ/K_0^\ast(700)$ and improve the constrains on their pole parameters. Subsequently improving our knowledge of the low-lying scalar nonet in general. △ Less

Submitted 4 March, 2021; v1 submitted 18 August, 2020; originally announced August 2020.

Comments: Final version of the KLF Proposal [C12-19-001] approved by JLab PAC48. The intermediate version of the proposal was posted in arXiv:1707.05284 [hep-ex]. 103 pages, 52 figures, 8 tables, 324 references. Several typos were fixed

An experimental program with high duty-cycle polarized and unpolarized positron beams at Jefferson Lab

Authors: A. Accardi, A. Afanasev, I. Albayrak, S. F. Ali, M. Amaryan, J. R. M. Annand, J. Arrington, A. Asaturyan, H. Atac, H. Avakian, T. Averett, C. Ayerbe Gayoso, X. Bai, L. Barion, M. Battaglieri, V. Bellini, R. Beminiwattha, F. Benmokhtar, V. V. Berdnikov, J. C. Bernauer, V. Bertone, A. Bianconi, A. Biselli, P. Bisio, P. Blunden , et al. (205 additional authors not shown)

Abstract: Positron beams, both polarized and unpolarized, are identified as essential ingredients for the experimental programs at the next generation of lepton accelerators. In the context of the hadronic physics program at Jefferson Lab (JLab), positron beams are complementary, even essential, tools for a precise understanding of the electromagnetic structure of nucleons and nuclei, in both the elastic an… ▽ More Positron beams, both polarized and unpolarized, are identified as essential ingredients for the experimental programs at the next generation of lepton accelerators. In the context of the hadronic physics program at Jefferson Lab (JLab), positron beams are complementary, even essential, tools for a precise understanding of the electromagnetic structure of nucleons and nuclei, in both the elastic and deep-inelastic regimes. For instance, elastic scattering of polarized and unpolarized electrons and positrons from the nucleon enables a model independent determination of its electromagnetic form factors. Also, the deeply-virtual scattering of polarized and unpolarized electrons and positrons allows unambiguous separation of the different contributions to the cross section of the lepto-production of photons and of lepton-pairs, enabling an accurate determination of the nucleons and nuclei generalized parton distributions, and providing an access to the gravitational form factors. Furthermore, positron beams offer the possibility of alternative tests of the Standard Model of particle physics through the search of a dark photon, the precise measurement of electroweak couplings, and the investigation of charged lepton flavor violation. This document discusses the perspectives of an experimental program with high duty-cycle positron beams at JLab. △ Less

Submitted 21 May, 2021; v1 submitted 29 July, 2020; originally announced July 2020.

Comments: 18 pages, 7 figures This version superseeds the previous version which scientific content was decomposed into several more elaborated articles. All of these articles will be collected in the EPJ A Topical Issue about "Positron beam and physics at Jefferson Lab (e+@Jlab)"

The GlueX Beamline and Detector

Authors: S. Adhikari, C. S. Akondi, H. Al Ghoul, A. Ali, M. Amaryan, E. G. Anassontzis, A. Austregesilo, F. Barbosa, J. Barlow, A. Barnes, E. Barriga, R. Barsotti, T. D. Beattie, J. Benesch, V. V. Berdnikov, G. Biallas, T. Black, W. Boeglin, P. Brindza, W. J. Briscoe, T. Britton, J. Brock, W. K. Brooks, B. E. Cannon, C. Carlin , et al. (165 additional authors not shown)

Abstract: The GlueX experiment at Jefferson Lab has been designed to study photoproduction reactions with a 9-GeV linearly polarized photon beam. The energy and arrival time of beam photons are tagged using a scintillator hodoscope and a scintillating fiber array. The photon flux is determined using a pair spectrometer, while the linear polarization of the photon beam is determined using a polarimeter based… ▽ More The GlueX experiment at Jefferson Lab has been designed to study photoproduction reactions with a 9-GeV linearly polarized photon beam. The energy and arrival time of beam photons are tagged using a scintillator hodoscope and a scintillating fiber array. The photon flux is determined using a pair spectrometer, while the linear polarization of the photon beam is determined using a polarimeter based on triplet photoproduction. Charged-particle tracks from interactions in the central target are analyzed in a solenoidal field using a central straw-tube drift chamber and six packages of planar chambers with cathode strips and drift wires. Electromagnetic showers are reconstructed in a cylindrical scintillating fiber calorimeter inside the magnet and a lead-glass array downstream. Charged particle identification is achieved by measuring energy loss in the wire chambers and using the flight time of particles between the target and detectors outside the magnet. The signals from all detectors are recorded with flash ADCs and/or pipeline TDCs into memories allowing trigger decisions with a latency of 3.3 $μ$s. The detector operates routinely at trigger rates of 40 kHz and data rates of 600 megabytes per second. We describe the photon beam, the GlueX detector components, electronics, data-acquisition and monitoring systems, and the performance of the experiment during the first three years of operation. △ Less

Submitted 26 October, 2020; v1 submitted 28 May, 2020; originally announced May 2020.

Comments: Accepted by Nuclear Instruments and Methods A, 78 pages, 54 figures

Report number: JLAB-PHY-20-3195

Journal ref: Nucl. Instrum. & Meth. A987, 164807 (2021)

Measurement of the Photon Beam Asymmetry in $\vecγ p\to K^+Σ^0$ at $E_γ = 8.5$ GeV

Authors: The GlueX Collaboration, S. Adhikari, A. Ali, M. Amaryan, A. Austregesilo, F. Barbosa, J. Barlow, E. Barriga, R. Barsotti, T. D. Beattie, V. V. Berdnikov, T. Black, W. Boeglin, W. J. Briscoe, T. Britton, W. K. Brooks, B. E. Cannon, N. Cao, E. Chudakov, S. Cole, O. Cortes, V. Crede, M. M. Dalton, T. Daniels, A. Deur , et al. (102 additional authors not shown)

Abstract: We report measurements of the photon beam asymmetry $Σ$ for the reaction $\vecγ p\to K^+Σ^0$(1193) using the GlueX spectrometer in Hall D at Jefferson Lab. Data were collected using a linearly polarized photon beam in the energy range of 8.2-8.8 GeV incident on a liquid hydrogen target. The beam asymmetry $Σ$ was measured as a function of the Mandelstam variable $t$, and a single value of $Σ$ was… ▽ More We report measurements of the photon beam asymmetry $Σ$ for the reaction $\vecγ p\to K^+Σ^0$(1193) using the GlueX spectrometer in Hall D at Jefferson Lab. Data were collected using a linearly polarized photon beam in the energy range of 8.2-8.8 GeV incident on a liquid hydrogen target. The beam asymmetry $Σ$ was measured as a function of the Mandelstam variable $t$, and a single value of $Σ$ was extracted for events produced in the $u$-channel. These are the first exclusive measurements of the photon beam asymmetry $Σ$ for the reaction in this energy range. For the $t$-channel, the measured beam asymmetry is close to unity over the $t$-range studied, $-t=(0.1-1.4)~$(GeV/$c$)$^{2}$, with an average value of $Σ= 1.00\pm 0.05$. This agrees with theoretical models that describe the reaction via the natural-parity exchange of the $K^{*}$(892) Regge trajectory. A value of $Σ= 0.41 \pm 0.09$ is obtained for the $u$-channel integrated up to $-u=2.0$~(GeV/$c$)$^{2}$. △ Less

Submitted 12 May, 2020; v1 submitted 18 March, 2020; originally announced March 2020.

Journal ref: Phys. Rev. C 101, 065206 (2020)

Conceptual Design of Beryllium Target for the KLF Project

Authors: Igor Strakovsky, Moskov Amaryan, Mikhail Bashkanov, William J. Briscoe, Eugene Chudakov, Pavel Degtyarenko, Sean Dobbs, Alexander Laptev, Ilya Larin, Alexander Somov, Timothy Whitlatch

Abstract: The Kaon Production Target (KPT) is an important component of the proposed K-Long facility which will be operated in JLab Hall~D, targeting strange baryon and meson spectroscopy. In this note we present a conceptual design for the Be-target assembly for the planned K-Long beam line, which will be used along with the GlueX spectrometer in its standard configuration for the proposed experiments. The… ▽ More The Kaon Production Target (KPT) is an important component of the proposed K-Long facility which will be operated in JLab Hall~D, targeting strange baryon and meson spectroscopy. In this note we present a conceptual design for the Be-target assembly for the planned K-Long beam line, which will be used along with the GlueX spectrometer in its standard configuration for the proposed experiments. The high quality 12-GeV CEBAF electron beam enables production of a K$_L$ flux at the GlueX target on the order of $1\times 10^4 K_L/sec$, which exceeds the K$_L$ flux previously attained at SLAC by three orders of magnitude. An intense K$_L$ beam would open a new window of opportunity not only to locate "missing resonances" in the strange hadron spectrum, but also to establish their properties by studying different decay channels systematically. The most important and radiation damaging background in K$_L$ production is due to neutrons. The Monte Carlo simulations for the proposed conceptual design of KPT show that the resulting neutron and gamma flux lead to a prompt radiation dose rate for the KLF experiment that is below the JLab Radiation Control Department radiation dose rate limits in the experimental hall and at the site boundary, and will not substantially affect the performance of the spectrometer. △ Less

Submitted 10 February, 2020; originally announced February 2020.

Comments: 9 pages, 9 figures

Scintillating crystals for the Neutral Particle Spectrometer in Hall C at JLab

Authors: T. Horn, V. V. Berdnikov, S. Ali, A. Asaturyan, M. Carmignotto, J. Crafts, A. Demarque, R. Ent, G. Hull, H. -S. Ko, M. Mostafavi, C. Munoz-Camacho, A. Mkrtchyan, H. Mkrtchyan, T. Nguyen Trung, I. L. Pegg, E. Rindel, A. Somov, V. Tadevosyan, R. Trotta, S. Zhamkochyan, R. Wang, S. A. Wood

Abstract: This paper discusses the quality and performance of currently available PbWO$_4$ crystals of relevance to high-resolution electromagnetic calorimetry, e.g. detectors for the Neutral Particle Spectrometer at Jefferson Lab or those planned for the Electron-Ion Collider. Since the construction of the Compact Muon Solenoid (CMS) at the Large Hadron Collider (LHC) and early PANDA (The antiProton ANnihi… ▽ More This paper discusses the quality and performance of currently available PbWO$_4$ crystals of relevance to high-resolution electromagnetic calorimetry, e.g. detectors for the Neutral Particle Spectrometer at Jefferson Lab or those planned for the Electron-Ion Collider. Since the construction of the Compact Muon Solenoid (CMS) at the Large Hadron Collider (LHC) and early PANDA (The antiProton ANnihilations at DArmstadt) electromagnetic calorimeter (ECAL) the worldwide availability of high quality PbWO$_4$ production has changed dramatically. We report on our studies of crystal samples from SICCAS/China and CRYTUR/Czech Republic that were produced between 2014 and 2019. △ Less

Submitted 24 November, 2019; originally announced November 2019.

Comments: 20 pages, 30 figures

Beam Asymmetry $\mathbfΣ$ for the Photoproduction of $\mathbfη$ and $\mathbf{η^{\prime}}$ Mesons at $\mathbf{E_γ=8.8}$GeV

Authors: The GlueX Collaboration, S. Adhikari, A. Ali, M. Amaryan, A. Austregesilo, F. Barbosa, J. Barlow, A. Barnes, E. Barriga, R. Barsotti, T. D. Beattie, V. V. Berdnikov, T. Black, W. Boeglin, M. Boer, W. J. Briscoe, T. Britton, W. K. Brooks, B. E. Cannon, N. Cao, E. Chudakov, S. Cole, O. Cortes, V. Crede, M. M. Dalton , et al. (109 additional authors not shown)

Abstract: We report on the measurement of the beam asymmetry $Σ$ for the reactions $\vecγp\rightarrow pη$ and $\vecγp \rightarrow pη^{\prime}$ from the GlueX experiment, using an 8.2--8.8 GeV linearly polarized tagged photon beam incident on a liquid hydrogen target in Hall D at Jefferson Lab. These measurements are made as a function of momentum transfer $-t$, with significantly higher statistical precisio… ▽ More We report on the measurement of the beam asymmetry $Σ$ for the reactions $\vecγp\rightarrow pη$ and $\vecγp \rightarrow pη^{\prime}$ from the GlueX experiment, using an 8.2--8.8 GeV linearly polarized tagged photon beam incident on a liquid hydrogen target in Hall D at Jefferson Lab. These measurements are made as a function of momentum transfer $-t$, with significantly higher statistical precision than our earlier $η$ measurements, and are the first measurements of $η^{\prime}$ in this energy range. We compare the results to theoretical predictions based on $t$--channel quasi-particle exchange. We also compare the ratio of $Σ_η$ to $Σ_{η^{\prime}}$ to these models, as this ratio is predicted to be sensitive to the amount of $s\bar{s}$ exchange in the production. We find that photoproduction of both $η$ and $η^{\prime}$ is dominated by natural parity exchange with little dependence on $-t$. △ Less

Submitted 24 November, 2019; v1 submitted 15 August, 2019; originally announced August 2019.

Comments: 18 pages, 7 figures

Report number: GlueX-Doc 4093

Journal ref: Phys. Rev. C 100, 052201 (2019)

Physics with Positron Beams at Jefferson Lab 12 GeV

Authors: A. Afanasev, I. Albayrak, S. Ali, M. Amaryan, A. D'Angelo, J. Annand, J. Arrington, A. Asaturyan, H. Avakian, T. Averett, L. Barion, M. Battaglieri, V. Bellini, V. Berdnikov, J. Bernauer, A. Biselli, M. Boer, M. Bondì, K. -T. Brinkmann, B. Briscoe, V. Burkert, A. Camsonne, T. Cao, L. Cardman, M. Carmignotto , et al. (102 additional authors not shown)

Abstract: Positron beams, both polarized and unpolarized, are identified as essential ingredients for the experimental program at the next generation of lepton accelerators. In the context of the Hadronic Physics program at the Jefferson Laboratory (JLab), positron beams are complementary, even essential, tools for a precise understanding of the electromagnetic structure of the nucleon, in both the elastic… ▽ More Positron beams, both polarized and unpolarized, are identified as essential ingredients for the experimental program at the next generation of lepton accelerators. In the context of the Hadronic Physics program at the Jefferson Laboratory (JLab), positron beams are complementary, even essential, tools for a precise understanding of the electromagnetic structure of the nucleon, in both the elastic and the deep-inelastic regimes. For instance, elastic scattering of (un)polarized electrons and positrons off the nucleon allows for a model independent determination of the electromagnetic form factors of the nucleon. Also, the deeply virtual Compton scattering of (un)polarized electrons and positrons allows us to separate unambiguously the different contributions to the cross section of the lepto-production of photons, enabling an accurate determination of the nucleon Generalized Parton Distributions (GPDs), and providing an access to its Gravitational Form Factors. Furthermore, positron beams offer the possibility of alternative tests of the Standard Model through the search of a dark photon or the precise measurement of electroweak couplings. This letter proposes to develop an experimental positron program at JLab to perform unique high impact measurements with respect to the two-photon exchange problem, the determination of the proton and the neutron GPDs, and the search for the $A^{\prime}$ dark photon. △ Less

Submitted 22 June, 2019; originally announced June 2019.

Comments: Letter-of-Intent to Jefferson Lab PAC46

Report number: Jefferson Lab LOI12-18-004

First measurement of near-threshold J/$ψ$ exclusive photoproduction off the proton

Authors: The GlueX Collaboration, A. Ali, M. Amaryan, E. G. Anassontzis, A. Austregesilo, M. Baalouch, F. Barbosa, J. Barlow, A. Barnes, E. Barriga, T. D. Beattie, V. V. Berdnikov, T. Black, W. Boeglin, M. Boer, W. J. Briscoe, T. Britton, W. K. Brooks, B. E. Cannon, N. Cao, E. Chudakov, S. Cole, O. Cortes, V. Crede, M. M. Dalton , et al. (110 additional authors not shown)

Abstract: We report on the measurement of the $γp \rightarrow J/ψp$ cross section from $E_γ= 11.8$ GeV down to the threshold at $8.2$ GeV using a tagged photon beam with the GlueX experiment. We find the total cross section falls toward the threshold less steeply than expected from two-gluon exchange models. The differential cross section $dσ/dt$ has an exponential slope of $1.67 \pm 0.39$ GeV$^{-2}$ at… ▽ More We report on the measurement of the $γp \rightarrow J/ψp$ cross section from $E_γ= 11.8$ GeV down to the threshold at $8.2$ GeV using a tagged photon beam with the GlueX experiment. We find the total cross section falls toward the threshold less steeply than expected from two-gluon exchange models. The differential cross section $dσ/dt$ has an exponential slope of $1.67 \pm 0.39$ GeV$^{-2}$ at $10.7$ GeV average energy. The LHCb pentaquark candidates $P_c^+$ can be produced in the $s$-channel of this reaction. We see no evidence for them and set model-dependent upper limits on their branching fractions $\mathcal{B}(P_c^+ \rightarrow J/ψp)$ and cross sections $σ(γp \to P_c^+)\times\mathcal{B}(P_c^+ \to J/ψp) $. △ Less

Submitted 10 September, 2019; v1 submitted 26 May, 2019; originally announced May 2019.

Comments: 12 pages, 7 figures

Journal ref: Phys. Rev. Lett. 123, 072001 (2019)

Measurement of the beam asymmetry $Σ$ for $π^0$ and $η$ photoproduction on the proton at $E_γ= 9$ GeV

Authors: GlueX Collaboration, H. Al Ghoul, E. G. Anassontzis, A. Austregesilo, F. Barbosa, A. Barnes, T. D. Beattie, D. W. Bennett, V. V. Berdnikov, T. Black, W. Boeglin, W. J. Briscoe, W. K. Brooks, B. E. Cannon, O. Chernyshov, E. Chudakov, V. Crede, M. M. Dalton, A. Deur, S. Dobbs, A. Dolgolenko, M. Dugger, R. Dzhygadlo, H. Egiyan, P. Eugenio , et al. (101 additional authors not shown)

Abstract: We report measurements of the photon beam asymmetry $Σ$ for the reactions $\vecγp\to pπ^0$ and $\vecγp\to pη$ from the GlueX experiment using a 9 GeV linearly-polarized, tagged photon beam incident on a liquid hydrogen target in Jefferson Lab's Hall D. The asymmetries, measured as a function of the proton momentum transfer, possess greater precision than previous $π^0$ measurements and are the fir… ▽ More We report measurements of the photon beam asymmetry $Σ$ for the reactions $\vecγp\to pπ^0$ and $\vecγp\to pη$ from the GlueX experiment using a 9 GeV linearly-polarized, tagged photon beam incident on a liquid hydrogen target in Jefferson Lab's Hall D. The asymmetries, measured as a function of the proton momentum transfer, possess greater precision than previous $π^0$ measurements and are the first $η$ measurements in this energy regime. The results are compared with theoretical predictions based on $t$-channel, quasi-particle exchange and constrain the axial-vector component of the neutral meson production mechanism in these models. △ Less

Submitted 15 May, 2017; v1 submitted 27 January, 2017; originally announced January 2017.

Comments: 6 pages, 6 figures, Published in Physical Review C: Rapid Communication

Report number: JLAB-PHY-17-2403

Journal ref: Phys. Rev. C 95, 042201 (2017)

First Results from The GlueX Experiment

Authors: The GlueX Collaboration, H. Al Ghoul, E. G. Anassontzis, F. Barbosa, A. Barnes, T. D. Beattie, D. W. Bennett, V. V. Berdnikov, T. Black, W. Boeglin, W. K. Brooks, B. Cannon, O. Chernyshov, E. Chudakov, V. Crede, M. M. Dalton, A. Deur, S. Dobbs, A. Dolgolenko, M. Dugger, H. Egiyan, P. Eugenio, A. M. Foda, J. Frye, S. Furletov , et al. (86 additional authors not shown)

Abstract: The GlueX experiment at Jefferson Lab ran with its first commissioning beam in late 2014 and the spring of 2015. Data were collected on both plastic and liquid hydrogen targets, and much of the detector has been commissioned. All of the detector systems are now performing at or near design specifications and events are being fully reconstructed, including exclusive production of $π^{0}$, $η$ and… ▽ More The GlueX experiment at Jefferson Lab ran with its first commissioning beam in late 2014 and the spring of 2015. Data were collected on both plastic and liquid hydrogen targets, and much of the detector has been commissioned. All of the detector systems are now performing at or near design specifications and events are being fully reconstructed, including exclusive production of $π^{0}$, $η$ and $ω$ mesons. Linearly-polarized photons were successfully produced through coherent bremsstrahlung and polarization transfer to the $ρ$ has been observed. △ Less

Submitted 14 January, 2016; v1 submitted 11 December, 2015; originally announced December 2015.

Comments: 8 pages, 6 figures, Invited contribution to the Hadron 2015 Conference, Newport News VA, September 2015

Report number: JLAB-PHY-16-2195

Journal ref: AIP Conf. Proc. 1735, 020001 (2016)

MesonNet 2014 International Workshop. Mini-proceedings

Authors: P. Adlarson, M. Bashkanov, J. Bijnens, L. Caldeira Balkeståhl, B. Cao, G. Colangelo, F. Curciarello, V. De Leo, K. Demmich, G. Eichmann, S. Eidelman, S. Fang, C. F. Redmer, C. Fritzsch, A. Gajos, S. Giovannella, S. Gonzàlez-Solís, E. Goudzovski, L. Heijkenskjöld, M. Hoferichter, T. Husek, N. Hüsken, W. I. Andersson, T. Kadavý, D. Kamińska , et al. (21 additional authors not shown)

Abstract: The MesonNet International Workshop was held in the Laboratori Nazionali di Frascati from September the 29th to October the 1st, 2014, being the concluding meeting of the MesonNet research network within EU HadronPhysics3 project. MesonNet is a research network focused on light meson physics gathering experimentalist and theoreticians from Europe and abroad. An overview of the research projects re… ▽ More The MesonNet International Workshop was held in the Laboratori Nazionali di Frascati from September the 29th to October the 1st, 2014, being the concluding meeting of the MesonNet research network within EU HadronPhysics3 project. MesonNet is a research network focused on light meson physics gathering experimentalist and theoreticians from Europe and abroad. An overview of the research projects related to the scope of the network is presented in these mini-proceedings. △ Less

Submitted 17 December, 2014; originally announced December 2014.

Comments: 93 pages, 12 figures, MesonNet 2014 International Workshop, 29/9 - 1/10 Frascati LNF INFN

Report number: MITP/14-089, MCTP-14-08

An initial study of mesons and baryons containing strange quarks with GlueX

Authors: The GlueX Collaboration, A. AlekSejevs, S. Barkanova, M. Dugger, B. Ritchie, I. Senderovich, E. Anassontzis, P. Ioannou, C. Kourkoumeli, G. Voulgaris, N. Jarvis, W. Levine, P. Mattione, W. McGinley, C. A. Meyer, R. Schumacher, M. Staib, P. Collins, F. Klein, D. Sober, D. Doughty, A. Barnes, R. Jones, J. McIntyre, F. Mokaya , et al. (75 additional authors not shown)

Abstract: The primary motivation of the GlueX experiment is to search for and ultimately study the pattern of gluonic excitations in the meson spectrum produced in $γp$ collisions. Recent lattice QCD calculations predict a rich spectrum of hybrid mesons that have both exotic and non-exotic $J^{PC}$, corresponding to $q\bar{q}$ states ($q=u,$ $d,$ or $s$) coupled with a gluonic field. A thorough study of the… ▽ More The primary motivation of the GlueX experiment is to search for and ultimately study the pattern of gluonic excitations in the meson spectrum produced in $γp$ collisions. Recent lattice QCD calculations predict a rich spectrum of hybrid mesons that have both exotic and non-exotic $J^{PC}$, corresponding to $q\bar{q}$ states ($q=u,$ $d,$ or $s$) coupled with a gluonic field. A thorough study of the hybrid spectrum, including the identification of the isovector triplet, with charges 0 and $\pm1$, and both isoscalar members, $|s\bar{s}\ >$ and $|u\bar{u}\ > + |d\bar{d}\ >$, for each predicted hybrid combination of $J^{PC}$, may only be achieved by conducting a systematic amplitude analysis of many different hadronic final states. Detailed studies of the performance of the \gx detector have indicated that identification of particular final states with kaons is possible using the baseline detector configuration. The efficiency of kaon detection coupled with the relatively lower production cross section for particles containing hidden strangeness will require a high intensity run in order for analyses of such states to be feasible. We propose to collect a total of 200 days of physics analysis data at an average intensity of $5\times 10^7$ tagged photons on target per second. This data sample will provide an order of magnitude statistical improvement over the initial GlueX running, which will allow us to begin a program of studying mesons and baryons containing strange quarks. In addition, the increased intensity will permit us to study reactions that may have been statistically limited in the initial phases of GlueX. Overall, this will lead to a significant increase in the potential for \gx to make key experimental advances in our knowledge of hybrid mesons and excited $Ξ$ baryons. △ Less

Submitted 7 May, 2013; originally announced May 2013.

Comments: 22 pages, 8 figures

A measurement of the energy and timing resolution of GlueX Forward Calorimeter using an electron beam

Authors: Kei Moriya, John P. Leckey, Matthew R. Shepherd, Kevin Bauer, Daniel Bennett, John Frye, Juan Gonzalez, Scott J. Henderson, David Lawrence, Ryan Mitchell, Elton S. Smith, Paul Smith, Alexander Somov, Hovanes Egiyan

Abstract: The performance of the GlueX Forward Calorimeter was studied using a small version of the detector and a variable energy electron beam derived from the Hall B tagger at Jefferson Lab. For electron energies from 110 MeV to 260 MeV, which are near the lower-limits of the design sensitivity, the fractional energy resolution was measured to range from 20% to 14%, which meets the design goals. The use… ▽ More The performance of the GlueX Forward Calorimeter was studied using a small version of the detector and a variable energy electron beam derived from the Hall B tagger at Jefferson Lab. For electron energies from 110 MeV to 260 MeV, which are near the lower-limits of the design sensitivity, the fractional energy resolution was measured to range from 20% to 14%, which meets the design goals. The use of custom 250 MHz flash ADCs for readout allowed precise measurements of signal arrival times. The detector achieved timing resolutions of 0.38 ns for a single 100 mV pulse, which will allow timing discrimination of photon beam bunches and out-of-time background during the operation of the GlueX detector. △ Less

Submitted 17 April, 2013; originally announced April 2013.

Comments: 8 pages, 11 figures, submitted to NIMA

A study of meson and baryon decays to strange final states with GlueX in Hall D (A proposal to the 39th Jefferson Lab Program Advisory Committee)

Authors: The GlueX Collaboration, M. Dugger, B. Ritchie, E. Anassontzis, P. Ioannou, C. Kourkoumeli, G. Voulgaris, N. Jarvis, W. Levine, P. Mattione, C. A. Meyer, R. Schumacher, P. Collins, F. Klein, D. Sober, D. Doughty, A. Barnes, R. Jones, J. McIntyre, F. Mokaya, B. Pratt, I. Senderovich, W. Boeglin, L. Guo, P. Khetarpal , et al. (54 additional authors not shown)

Abstract: The primary motivation of the GlueX experiment is to search for and ultimately study the pattern of gluonic excitations in the meson spectrum produced in gamma p collisions. Recent lattice QCD calculations predict a rich spectrum of hybrid mesons that have both exotic and non-exotic JPC, corresponding to q q-bar (q=u, d, or s) states coupled with a gluonic field. A thorough study of the hybrid spe… ▽ More The primary motivation of the GlueX experiment is to search for and ultimately study the pattern of gluonic excitations in the meson spectrum produced in gamma p collisions. Recent lattice QCD calculations predict a rich spectrum of hybrid mesons that have both exotic and non-exotic JPC, corresponding to q q-bar (q=u, d, or s) states coupled with a gluonic field. A thorough study of the hybrid spectrum, including the identification of the isovector triplet, with charges 0 and +-1, and both isoscalar members, |s s-bar> and |u u-bar> + |d d-bar>, for each predicted hybrid combination of JPC, may only be achieved by conducting a systematic amplitude analysis of many different hadronic final states. We propose the development of a kaon identification system, supplementing the existing GlueX forward time-of-flight detector, in order to cleanly select meson and baryon decay channels that include kaons. Once this detector has been installed and commissioned, we plan to collect a total of 200 days of physics analysis data at an average intensity of 5 x 10^7 tagged photons on target per second. This data sample will provide an order of magnitude statistical improvement over the initial GlueX data set and, with the developed kaon identification system, a significant increase in the potential for GlueX to make key experimental advances in our knowledge of hybrid mesons and Cascade baryons. △ Less

Submitted 16 October, 2012; originally announced October 2012.

Comments: 20 pages, 9 figures (submitted to the 39th Jefferson Lab PAC)

Report number: GlueX-doc 1962

Abundance of Delta Resonances in 58Ni+58Ni Collisions between 1 and 2 AGeV

Authors: FOPI Collaboration, B. Hong, N. Herrmann, J. L. Ritman, D. Best, A. Gobbi, K. D. Hildenbrand, M. Kirejczyk, Y. Leifels, C. Pinkenburg, W. Reisdorf, D. Schuell, U. Sodan, G. S. Wang, T. Wienold, J. P. Alard, V. Amouroux, N. Bastid, I. Belyaev, G. Berek, J. Biegansky, A. Buta, J. P. Coffin, P. Crochet, R. Dona , et al. (37 additional authors not shown)

Abstract: Charged pion spectra measured in 58Ni-58Ni collisions at 1.06, 1.45 and 1.93 AGeV are interpreted in terms of a thermal model including the decay of Delta resonances. The transverse momentum spectra of pions are well reproduced by adding the pions originating from the Delta-resonance decay to the component of thermal pions, deduced from the high transverse momentum part of the pion spectra. Abou… ▽ More Charged pion spectra measured in 58Ni-58Ni collisions at 1.06, 1.45 and 1.93 AGeV are interpreted in terms of a thermal model including the decay of Delta resonances. The transverse momentum spectra of pions are well reproduced by adding the pions originating from the Delta-resonance decay to the component of thermal pions, deduced from the high transverse momentum part of the pion spectra. About 10 and 18% of the nucleons are excited to Delta states at freeze-out for beam energies of 1 and 2 AGeV, respectively. △ Less

Submitted 4 June, 1997; originally announced June 1997.

Comments: 14 pages, LaTeX with 3 included figures; submitted to Physics Letters B

Journal ref: Phys.Lett.B407:115-120,1997