We measure the spin-density matrix elements (SDMEs) of the Delta(++)(1232) in the photoproduction reaction gamma p -> pi(-) Delta(++)(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 8.8GeV and the statistical precision of the SDMEs exceeds the previous measurement by three orders of magnitude for the momentum transfer squared region below 1.4GeV(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.

This White Paper presents an overview of the current status and future perspective of QCD research, based on the community inputs and scientific conclusions from the 2022 Hot and Cold QCD Town Meeting. We present the progress made in the last decade toward a deep understanding of both the fundamental structure of the sub-atomic matter of nucleon and nucleus in cold QCD, and the hot QCD matter in heavy ion collisions. We identify key questions of QCD research and plausible paths to obtaining answers to those questions in the near future, hence defining priorities of our research over the coming decades.

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.

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→ωπ^{+}π^{-}p, γp→ωπ^{0}π^{0}p, and γp→ωπ^{-}π^{0}Δ^{++} 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_{1}^{0}(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).

. - Close to threshold photoproduction -yp -+ J/psi p probes small -size gluon configurations in the proton. Under certain assumptions, it allows us to study the proton properties, as gluonic GPDs, anomalous contribution to the mass of the proton, gravitational form factors, and the mass radius of the proton. A careful comparison of the experimental data with the theoretical predictions would help us to verify the validity of those assumptions. The first cross-section measurements of near-threshold reaction -yp -+ J/psi p by the GlueX Collaboration (ALI A. et al. , Phys. Rev. Lett. , 123 (2019) 072001) has attracted a considerable theoretical interest. Along with the relation to the gluonic properties of the proton, the measurement exploited a possibility of the LHCb Pentaquark (P) production in the s -channel of the observed reaction, placing a limit on the decay probability P -+ J/psi p . Here we present new GlueX results (ADHIKARI S. et al. , Phys. Rev. C , 108 (2023) 025201) based on a four-times larger data set. The higher statistics, along with the full acceptance of the GlueX spectrometer allows us to measure the differential crosssection in several energy ranges and compare the results with several theoretical calculations. The new results have already been used in a number of theoretical papers.

The GlueX experiment at Jefferson Lab studies photoproduction of mesons using linearly polarized 8.5 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 rho(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 rho(770) differ by two units are negligible for -t < 0.5 GeV2/c(2).

New high-statistics total cross-section data for $\ensuremath{\gamma}p\ensuremath{\rightarrow}J/\ensuremath{\psi}p$ from the gluonic excitation (GlueX) experiment are fitted in a search for the exotic ${P}_{c}{(4312)}^{+}$ state observed by the Large Hadron Collider beauty (LHCb) Collaboration. The integrated luminosity of this GlueX experiment was about 320 ${\mathrm{pb}}^{\ensuremath{-}1}$. The fits show that destructive interference involving an $S$-wave resonance and associated nonresonance background produces a sharp dip structure about 77 MeV below the LHCb mass, in the same location as a similar structure is seen in the data. Limitations of the employed model and the need for improved statistics are discussed.

and GRETINA a 1{pi} detector is under construction. However, the momentum in developing this technology to its full potential must continue towards GRETA, a full 4{pi} calorimeter. GRETA will carry {gamma}-ray spectroscopy into the next generation where it will be needed to fully exploit the science opportunities at radioactive beam facilities and increase the reach of stable beam facilities. In addition, {gamma}-ray tracking technology will have important applications for science, medicine, and homeland security.

New high-statistics total cross section data for $\gamma p\to J/\psi p$ from the GLUonic EXcitation (GlueX) experiment are fitted in a search for the exotic $P_c(4312)^+$ state observed by the Large Hadron Collider beauty (LHCb) collaboration. The integrated luminosity of this GlueX experiment was about $320~\mathrm{pb^{-1}}$. The fits show that destructive interference involving an $S$-wave resonance and associated non-resonance background produces a sharp dip structure about $75~\mathrm{MeV}$ below the LHCb mass, in the same location as a similar structure is seen in the data. Limitations of the employed model and the need for improved statistics are discussed.

We report the total and differential cross sections for J/& psi; 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/& psi; photoproduction and its relation to the J/& psi;-proton interaction. These measurements of J/& psi; 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 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.

The gravitational form factors (GFFs) are a fundamental and elegant way to describe the structure of nucleons and nuclei. Their Fourier transform allows a description of the spatial distribution of the mass, angular momentum, pressure, and shear force densities for both quarks and gluons in the nucleon. While previous investigations predominantly focused on the proton electromagnetic form factors (EMFFs) leading to the charge and magnetization distributions determination, the current emphasis has shifted towards expanding our understanding of the gravitational form factors of quarks and gluons where little is known. In particular, more recently, the proton {\it gluonic} GFFs have been the target of an intensive investigation at Jefferson Lab. This endeavor, is not without its challenges, particularly in navigating the complexities associated with the near-threshold region. Nevertheless, it provides a bedrock for future nucleon and nuclei gluonic structure studies at the future EIC. In this talk, I will focus on the recent results of $J/\psi$ photoproduction near-threshold on the proton at Jefferson Lab to determine, in particular, the elusive {\it gluonic} gravitational form factors. We discuss the caveats of their extraction in the threshold region and mention the complementary measurements of $\Upsilon$ at the EIC critical to access the trace anomaly and gain insight into the origin of the nucleon mass.

The proton is one of the main building blocks of all visible matter in the universe. Among its intrinsic properties are its electric charge, mass, and spin. These emerge from the complex dynamics of its fundamental constituents, quarks and gluons, described by the theory of quantum chromodynamics (QCD). Using electron scattering its electric charge and spin, shared among the quark constituents, have been the topic of active investigation until today. An example is the novel precision measurement of the proton's electric charge radius. In contrast, little is known about the proton's inner mass density, dominated by the energy carried by the gluons, which are hard to access through electron scattering since gluons carry no electromagnetic charge. In the present work we chose to probe this gluonic gravitational density using a small color dipole, the $J/\psi$ particle, through its threshold photoproduction. From our data we determined, for the first time, the proton's gluonic gravitational form factors, which encode its mass density. We used a variety of methods and determined in all cases a mass radius that is notably smaller than the electric charge radius. In some cases, the determined radius is in excellent agreement with first-principle predictions from lattice QCD. This work paves the way for a deeper understanding of the salient role of gluons in providing gravitational mass to visible matter.

The GlueX experiment at Jefferson Laboratory aims to perform quantitative tests of non-perturbative QCD by studying the spectrum of light-quark mesons and baryons. A Detector of Internally Reflected Cherenkov light (DIRC) was installed to enhance the particle identification (PID) capability of the GlueX experiment by providing clean π/K separation up to 3.7 GeV/c momentum in the forward region (θ < 11°), which will allow the study of hybrid mesons decaying into kaon final states with significantly higher efficiency and purity. The new PID system is constructed with radiators from the decommissioned BaBar DIRC counter, combined with new compact photon cameras based on the SuperB FDIRC concept. The full system was successfully installed and commissioned with beam during 2019/2020. The initial PID performance of the system was evaluated and compared to one from Geant4 simulation.

We summarize the ongoing scientific program of the 12 GeV Continuous Electron Beam Accelerator Facility (CEBAF) and give an outlook into future scientific opportunities. The program addresses important topics in nuclear, hadronic, and electroweak physics including nuclear femtography, meson and baryon spectroscopy, quarks and gluons in nuclei, precision tests of the standard model, and dark sector searches. Potential upgrades of CEBAF are considered, such as higher luminosity, polarized and unpolarized positron beams, and doubling the beam energy.

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, M. M. Dalton, T. Daniels, A. Deur, S. Dobbs, A. Dolgolenko, R. Dotel, M. Dugger, R. Dzhygadlo, H. Egiyan, T. Erbora, A. Ernst, P. Eugenio, C. Fanelli, S. Fegan, ∗ J. Fitches, A. M. Foda, S. Furletov, L. Gan, H. Gao, A. Gasparian, C. Gleason, 28 K. Goetzen, V. S. Goryachev, L. Guo, M. Hagen, H. Hakobyan, A. Hamdi, J. Hernandez, N. D. Hoffman, G. Hou, G. M. Huber, A. Hurley, D. G. Ireland, M. M. Ito, I. Jaegle, N. S. Jarvis, R. T. Jones, V. Kakoyan, G. Kalicy, M. Kamel, V. Khachatryan, M. Khatchatryan, C. Kourkoumelis, S. Kuleshov, A. LaDuke, I. Larin, 14 D. Lawrence, D. I. Lersch, H. Li, W. B. Li, B. Liu, K. Livingston, G. J. Lolos, K. Luckas, V. Lyubovitskij, D. Mack, A. Mahmood, H. Marukyan, V. Matveev, M. McCaughan, M. McCracken, 29 C. A. Meyer, R. Miskimen, R. E. Mitchell, K. Mizutani, V. Neelamana, F. Nerling, L. Ng, A. I. Ostrovidov, Z. Papandreou, C. Paudel, P. Pauli, † R. Pedroni, L. Pentchev, K. J. Peters, J. Reinhold, B. G. Ritchie, J. Ritman, 15 G. Rodriguez, D. Romanov, C. Romero, K. Saldana, C. Salgado, S. Schadmand, A. M. Schertz, A. Schick, A. Schmidt, R. A. Schumacher, J. Schwiening, P. Sharp, X. Shen, M. R. Shepherd, A. Smith, E. S. Smith, D. I. Sober, A. Somov, S. Somov, O. Soto, J. R. Stevens, I. I. Strakovsky, B. Sumner, K. Suresh, V. V. Tarasov, S. Taylor, A. Teymurazyan, A. Thiel, G. Vasileiadis, T. Viducic, T. Whitlatch, N. Wickramaarachchi, M. Williams, Y. Yang, J. Zarling, Z. Zhang, Z. Zhao, J. Zhou, X. Zhou, Q. Zhou, and B. Zihlmann

We report on the measurement of spin density matrix elements of the (cid:2) (1520) in the photoproduction reaction γ p → (cid:2) (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 Laboratory using a linearly polarized photon beam with E γ = 8 . 2 GeV–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 0 ). We compare the results with a Reggeon exchange model and determine that natural exchange amplitudes are dominant in (cid:2) (1520) photoproduction.

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 → γγ and a → π + 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 → γγ decays is performed in the mass range of 180 < m a < 480 MeV, while the search for a → π + 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.

This report describes the physics case, the resulting detector requirements, and the evolving detector concepts for the experimental program at the Electron-Ion Collider (EIC). The EIC will be a powerful new high-luminosity facility in the United States with the capability to collide high-energy electron beams with high-energy proton and ion beams, providing access to those regions in the nucleon and nuclei where their structure is dominated by gluons. Moreover, polarized beams in the EIC will give unprecedented access to the spatial and spin structure of the proton, neutron, and light ions. The studies leading to this document were commissioned and organized by the EIC User Group with the objective of advancing the state and detail of the physics program and developing detector concepts that meet the emerging requirements in preparation for the realization of the EIC. The effort aims to provide the basis for further development of concepts for experimental equipment best suited for the science needs, including the importance of two complementary detectors and interaction regions. This report consists of three volumes. Volume I is an executive summary of our findings and developed concepts. In Volume II we describe studies of a wide range of physics measurements and the emerging requirements on detector acceptance and performance. Volume III discusses general-purpose detector concepts and the underlying technologies to meet the physics requirements. These considerations will form the basis for a world-class experimental program that aims to increase our understanding of the fundamental structure of all visible matter