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).

Quantum Chromodynamics, the theory of quarks and gluons, whose interactions can be described by a local SU(3) gauge symmetry with charges called “color quantum numbers”, is reviewed; the goal of this review is to provide advanced Ph.D. students a comprehensive handbook, helpful for their research. When QCD was “discovered” 50 years ago, the idea that quarks could exist, but not be observed, left most physicists unconvinced. Then, with the discovery of charmonium in 1974 and the explanation of its excited states using the Cornell potential, consisting of the sum of a Coulomb-like attraction and a long range linear confining potential, the theory was suddenly widely accepted. This paradigm shift is now referred to as the November revolution. It had been anticipated by the observation of scaling in deep inelastic scattering, and was followed by the discovery of gluons in three-jet events. The parameters of QCD include the running coupling constant, α _s(Q^2) , that varies with the energy scale Q^2 characterising the interaction, and six quark masses. QCD cannot be solved analytically, at least not yet, and the large value of α _s at low momentum transfers limits perturbative calculations to the high-energy region where Q^2≫ _QCD ^2≃ (250 MeV) ^2 . Lattice QCD (LQCD), numerical calculations on a discretized space-time lattice, is discussed in detail, the dynamics of the QCD vacuum is visualized, and the expected spectra of mesons and baryons are displayed. Progress in lattice calculations of the structure of nucleons and of quantities related to the phase diagram of dense and hot (or cold) hadronic matter are reviewed. Methods and examples of how to calculate hadronic corrections to weak matrix elements on a lattice are outlined. The wide variety of analytical approximations currently in use, and the accuracy of these approximations, are reviewed. These methods range from the Bethe–Salpeter, Dyson–Schwinger coupled relativistic equations, which are formulated in both Minkowski or Euclidean spaces, to expansions of multi-quark states in a set of basis functions using light-front coordinates, to the AdS/QCD method that imbeds 4-dimensional QCD in a 5-dimensional deSitter space, allowing confinement and spontaneous chiral symmetry breaking to be described in a novel way. Models that assume the number of colors is very large, i.e. make use of the large N_c -limit, give unique insights. Many other techniques that are tailored to specific problems, such as perturbative expansions for high energy scattering or approximate calculations using the operator product expansion are discussed. The very powerful effective field theory techniques that are successful for low energy nuclear systems (chiral effective theory), or for non-relativistic systems involving heavy quarks, or the treatment of gluon exchanges between energetic, collinear partons encountered in jets, are discussed. The spectroscopy of mesons and baryons has played an important historical role in the development of QCD. The famous X,Y,Z states – and the discovery of pentaquarks – have revolutionized hadron spectroscopy; their status and interpretation are reviewed as well as recent progress in the identification of glueballs and hybrids in light-meson spectroscopy. These exotic states add to the spectrum of expected qq̅ mesons and qqq baryons. The progress in understanding excitations of light and heavy baryons is discussed. The nucleon as the lightest baryon is discussed extensively, its form factors, its partonic structure and the status of the attempt to determine a three-dimensional picture of the parton distribution. An experimental program to study the phase diagram of QCD at high temperature and density started with fixed target experiments in various laboratories in the second half of the 1980s, and then, in this century, with colliders. QCD thermodynamics at high temperature became accessible to LQCD, and numerical results on chiral and deconfinement transitions and properties of the deconfined and chirally restored form of strongly interacting matter, called the Quark–Gluon Plasma (QGP), have become very precise by now. These results can now be confronted with experimental data that are sensitive to the nature of the phase transition. There is clear evidence that the QGP phase is created. This phase of QCD matter can already be characterized by some properties that indicate, within a temperature range of a few times the pseudocritical temperature, the medium behaves like a near ideal liquid. Experimental observables are presented that demonstrate deconfinement. High and ultrahigh density QCD matter at moderate and low temperatures shows interesting features and new phases that are of astrophysical relevance. They are reviewed here and some of the astrophysical implications are discussed. Perturbative QCD and methods to describe the different aspects of scattering processes are discussed. The primary parton–parton scattering in a collision is calculated in perturbative QCD with increasing complexity. The radiation of soft gluons can spoil the perturbative convergence, this can be cured by resummation techniques, which are also described here. Realistic descriptions of QCD scattering events need to model the cascade of quark and gluon splittings until hadron formation sets in, which is done by parton showers. The full event simulation can be performed with Monte Carlo event generators, which simulate the full chain from the hard interaction to the hadronic final states, including the modelling of non-perturbative components. The contribution of the LEP experiments (and of earlier collider experiments) to the study of jets is reviewed. Correlations between jets and the shape of jets had allowed the collaborations to determine the “color factors” – invariants of the SU(3) color group governing the strength of quark–gluon and gluon–gluon interactions. The calculated jet production rates (using perturbative QCD) are shown to agree precisely with data, for jet energies spanning more than five orders of magnitude. The production of jets recoiling against a vector boson, W^± or Z, is shown to be well understood. The discovery of the Higgs boson was certainly an important milestone in the development of high-energy physics. The couplings of the Higgs boson to massive vector bosons and fermions that have been measured so far support its interpretation as mass-generating boson as predicted by the Standard Model. The study of the Higgs boson recoiling against hadronic jets (without or with heavy flavors) or against vector bosons is also highlighted. Apart from the description of hard interactions taking place at high energies, the understanding of “soft QCD” is also very important. In this respect, Pomeron – and Odderon – exchange, soft and hard diffraction are discussed. Weak decays of quarks and leptons, the quark mixing matrix and the anomalous magnetic moment of the muon are processes which are governed by weak interactions. However, corrections by strong interactions are important, and these are reviewed. As the measured values are incompatible with (most of) the predictions, the question arises: are these discrepancies first hints for New Physics beyond the Standard Model? This volume concludes with a description of future facilities or important upgrades of existing facilities which improve their luminosity by orders of magnitude. The best is yet to come!

Past experiments [S. Depierreux et al., Phys. Rev. Lett. 102, 195005 (2009)] have exhibited the plasmainduced incoherence (PII) process and the reduced imprint in the multikilojoule regime when a thin low-density foam is disposed in front of a solid target. Complementary experiments have been designed to analyze the mechanisms involved, the important parameters, and the role of the optical smoothing in the case of the laser megajoule. Forward stimulated Brillouin scattering (FSBS) is identified as the dominant mechanism governing the angular spray of the laser. FSBS also increases the laser bandwidth and imparts levels of temporal and spatial incoherencies beyond the present capacities of the optical smoothing of the megajoule laser facilities. Such a PII beam becomes suitable to achieve the high degree of irradiation uniformity required to experiment high-convergence efficient direct-drive inertial confinement fusion configurations at the megajoule scale which would otherwise require major changes in the laser chains. By reducing backscattering losses and/or allowing less optically applied smoothing, PII could relax the constraints imposed on the laser system and open the road to an increase in the energy coupled to the target in indirect-drive experiments.

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).

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.

Abstract Aging is a major risk factor for impaired cardiovascular function. The aging heart is characterized by vascular dysfunction, increased hypertrophy, fibrosis and electrophysiological alterations. Studies show impaired endothelial cell (EC) function associates with senescence in aging. Since vessels and nerves align, and this interplay is critical for tissue homeostasis, we studied whether an impairment of the neuro-vascular interface may contribute to age-associated pathologies in the heart. To study the innervation of the aging mouse heart, we histologically assessed the cardiac autonomic nervous system in 3- and 20-month old mice using the pan-neuronal marker Tuj1 and the sympathetic marker TH. Interestingly, sympathetic innervation of the left ventricle, especially around arteries, was reduced by 0.66±0.07-fold with aging (p<0.05) indicating that aging reduces innervation of the left ventricle. Similar findings were observed in premature aging models of TERT-KO and EC-transgenic progeria mice. Electrophysiological studies confirmed an increased incidence of ventricular arrhythmias and reduced heart rate variability in aged mice. To determine the potential contribution of neurovascular cells, we analyzed gene expression of isolated ECs in aging mouse hearts by bulk RNA sequencing. Aging significantly induced the expression of genes associated with GO-terms related to neuronal cell death and axon injury. Sema3a, an axon repelling factor, was significantly increased in ECs of aged mice hearts, which was confirmed by qPCR and by histology (p<0.05). Next we determined the mechanism of Sema3a regulation. We show that miR-145 acts as an up-stream regulator of Sema3a expression. miR-145-/- mice showed increased Sema3a expression and reduced cardiac innervation. We observed an increase in acidic β-gal activity as a marker for cellular senescence in the aging heart, particularly in the proximate arterial space. In addition, Sema3a expression was significantly increased in senescent ECs in vitro, thus suggesting a putative role for senescence to impair cardiac innervation. To test whether eliminating senescent cells may restore left ventricular axon density, we treated 18-month old mice with a combination of the two senolytic drugs dasatinib and quercetin, which are known to deplete senescent cells in vivo. After 2 months of treatment, cellular senescence was reduced by 0.4±0.1-fold (p<0.05) in aged hearts. Endothelial expression of Sema3a was also reduced. Importantly, senolytic treatment restored ventricular innervation, augmented heart rate variability, and normalized electrophysiological abnormalities (all p<0.05). In conclusion, we show that aging augments axon repelling signals in ECs and reduces left ventricular innervation. The depletion of senescent cells prevented age-induced impairment of innervation and normalized electrophysiological abnormalities suggesting a critical role of senescence-associated axon repulsion in the aging heart.

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.

A bstract A search for the exclusive decays of the Higgs and Z bosons to a ϕ or ρ meson and a photon is performed with a pp collision data sample corresponding to an integrated luminosity of up to 35 . 6 fb −1 collected at $$ \sqrt{s}=13 $$ s = 13 TeV with the ATLAS detector at the CERN Large Hadron Collider. These decays have been suggested as a probe of the Higgs boson couplings to light quarks. No significant excess of events is observed above the background, as expected from the Standard Model. Upper limits at 95% confidence level were obtained on the branching fractions of the Higgs boson decays to ϕ γ and ρ γ of 4 . 8 × 10 −4 and 8 . 8 × 10 −4 , respectively. The corresponding 95% confidence level upper limits for the Z boson decays are 0 . 9 × 10 −6 and 25 × 10 −6 for ϕ γ and ρ γ, respectively.

A search for leptoquarks decaying into the bτ final state is performed using Run 2 proton-proton collision data from the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb−1 at √(s) = 13 TeV recorded by the ATLAS detector. The benchmark models considered in this search are vector leptoquarks with electric charge of 2/3e and scalar leptoquarks with an electric charge of 4/3e. No significant excess above the Standard Model prediction is observed, and 95

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.

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 mu 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.

This letter presents a search for narrow, high-mass resonances in the Zγ final state with the Z boson decaying into a pair of electrons or muons. The s=13 TeV pp collision data were recorded by the ATLAS detector at the CERN Large Hadron Collider and have an integrated luminosity of 140 fb−1. The data are found to be in agreement with the Standard Model background expectation. Upper limits are set on the resonance production cross section times the decay branching ratio into Zγ. For spin-0 resonances produced via gluon–gluon fusion, the observed limits at 95% confidence level vary between 65.5 fb and 0.6 fb, while for spin-2 resonances produced via gluon–gluon fusion (or quark–antiquark initial states) limits vary between 77.4 (76.1) fb and 0.6 (0.5) fb, for the mass range from 220 GeV to 3400 GeV.