Search

The trace of the stress tensor characterizes the transformation of a theory under rescaling. In quantum chromodynamics (QCD), this trace contains contributions from the bare masses of the quarks and also from a purely quantum effect, called the QCD trace anomaly. It affects all masses in the theory. We present an estimation of the QCD trace anomaly from the near-threshold J/${\rm \Psi}$ photo-production data of the GlueX experiment, at JLab. We apply a vector meson dominance model to describe the photo-production of J/${\rm \Psi}$ and a running strong coupling which includes the nonperturbative effects in the low $\mu^2$ region. Despite the large uncertainty, we find that the experimental data favors a small value of the trace anomaly parameter $b=0.07\pm 0.17$. We report the resulting proton mass decompositions at $\mu^2=0.41$ GeV$^2$ and $\mu^2=4$ GeV$^2$., Comment: 6 pages, 4 figures

We report a measurement of the π − photoproduction beam asymmetry for the reaction → γ p → 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.

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

The near threshold photo or electroproduction of heavy vector quarkonium off the proton is studied in quantum chromodynamics. Similar to the high-energy limit, the production amplitude can be factorized in terms of gluonic Generalized Parton Distributions and the quarkonium distribution amplitude. At the threshold, the threshold kinematics has a large skewness parameter $\xi$, leading to the dominance of the spin-2 contribution over higher-spin twist-2 operators. Thus threshold production data are useful to extract the gluonic gravitational form factors, allowing studying the gluonic contributions to the quantum anomalous energy, mass radius, spin and mechanical pressure in the proton. We use the recent GlueX data on the $J/\psi$ photoproduction to illustrate the potential physics impact from the high-precision data from future JLab 12 GeV and EIC physics program., Comment: 11 pages, 10 figures

A constituent gluon model that is informed by recent lattice field theory is developed. The model is then used to compute hybrid strong decay widths that could be useful for the GlueX Collaboration at Jefferson Lab and the PANDA Collaboration at FAIR. Commensurately, forthcoming data from GlueX and PANDA will test the model. Widths tend to be typical of charmonia, except for those of the lightest hybrid S-wave multiplet. Selection rules, extensions, limitations, and applications are discussed., Facultad de Ciencias Exactas

We report measurements of the photon beam asymmetry Σ for the reaction γp→K+Σ0 (1193) using the GlueX spectrometer in Hall D at Jefferson Lab. Data were collected by 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 ± 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 ± 0.09 is obtained for the u channel integrated up to − u = 2.0 ( GeV / c ) 2 .

The high accuracy $\phi $-meson photoproduction data from the CLAS experiment in Hall~B of Jefferson Laboratory allow us to determine the near-threshold total cross section of the $\gamma p\to\phi p$ reaction and use it for evaluating the $\phi p$ scattering length $\alpha_{\phi p}$. These data result in an absolute value of $|\alpha_{\phi p}| = (0.063\pm 0.010)$~fm, which is smaller than the typical hadron size. A comparative analysis of $\alpha_{\phi p}$ with the previously determined scattering lengths for $\omega p$ and $J/\psi p$ from the A2 and GlueX experiments is performed.

The quality of the recent GlueX $J/\psi $ photoproduction data from Hall~D at Jefferson Laboratory, and the proximity of the data to the energy threshold, gives access to a variety of interesting physics aspects. As an example, an estimation of the $J/\psi$-nucleon scattering length $\alpha_{J/\psi p}$ is provided within the vector meson dominance model. It results in $|\alpha_{J/\psi p}| = (3.08\pm 0.55 ({\rm stat.}) \pm 0.45 ({\rm syst.}))$~mfm., Comment: 5 pages, 2 figures, v1 had a typo

The near-threshold photo-productions of heavy quarkonia are important ways to test the QCD-inspired models and to constrain the gluon distribution of nucleon in the large x region. Investigating the various models, we choose a photon–gluon fusion model and a pomeron exchange model for $$\hbox {J}/\varPsi $$J/Ψ photo-production near threshold, emphasising on the explanation of the recent experimental measurement by GlueX at JLab. We find that these two models are not only valid in a wide range of the center-of-mass energy of $$\gamma $$γ and proton, but also can be generalized to describe the $$\varUpsilon \hbox {(1S)}$$Υ(1S) photo-production. Using these two models, we predict the electro-production cross-sections of $$\varUpsilon \hbox {(1S)}$$Υ(1S) at EicC to be 48 fb to 85 fb at the center-of-mass energy of 16.75 GeV.

This work reports a dynamical Markov state model of CLC-2 “fast” (pore) gating, based on 600 microseconds of molecular dynamics (MD) simulation. In the starting conformation of our CLC-2 model, both outer and inner channel gates are closed. The first conformational change in our dataset involves rotation of the inner-gate backbone along residues S168-G169-I170. This change is strikingly similar to that observed in the cryo-EM structure of the bovine CLC-K channel, though the volume of the intracellular (inner) region of the ion conduction pathway is further expanded in our model. From this state (inner gate open and outer gate closed), two additional states are observed, each involving a unique rotameric flip of the outer-gate residue GLUex. Both additional states involve conformational changes that orient GLUex away from the extracellular (outer) region of the ion conduction pathway. In the first additional state, the rotameric flip of GLUex results in an open, or near-open, channel pore. The equilibrium population of this state is low (∼1%), consistent with the low open probability of CLC-2 observed experimentally in the absence of a membrane potential stimulus (0 mV). In the second additional state, GLUex rotates to occlude the channel pore. This state, which has a low equilibrium population (∼1%), is only accessible when GLUex is protonated. Together, these pathways model the opening of both an inner and outer gate within the CLC-2 selectivity filter, as a function of GLUex protonation. Collectively, our findings are consistent with published experimental analyses of CLC-2 gating and provide a high-resolution structural model to guide future investigations., Author summary In contrast to sodium-, potassium-, and calcium-selective ion channels, the roles of chloride-selective ion channels in mammalian physiology have been studied much less and are not sufficiently understood, despite known associations of chloride-channel defects with a variety of pathological conditions. CLC-2 is a voltage-activated chloride channel (one of 9 human CLC homologs) with broad tissue and organ distribution. In this work, we use simulations to model the conformational dynamics of the CLC-2 chloride ion channel selectivity filter (SF), which is the part of the protein that controls whether the channel is in an ion-conducting or non-conducting state. Our analysis identifies four primary conformational states and a specific progression through these states. Our results are consistent with structural and functional data in the literature and provide a high-resolution model for guiding further studies of CLC-2. These results will inform our understanding of how CLC-2 regulates electrical activity and ion homeostasis in the many tissues where it is expressed.

Hybrid/exotic meson spectroscopy searches at Jefferson Lab require the accurate theoretical description of the production mechanism in peripheral photoproduction. We develop a model for π Δ photoproduction at high energies ( 5 ≤ E lab ≤ 16 GeV ) that incorporates both the absorbed pion and natural-parity cut contributions. We fit the available observables, providing a good description of the energy and angular dependencies of the experimental data. We also provide predictions for the photon beam asymmetry of charged pions at E lab = 9 GeV which is expected to be measured by GlueX and CLAS12 experiments in the near future.

A new electromagnetic calorimeter consisting of 140 lead tungstate (PbWO 4 ) scintillating crystals was constructed for the PrimEx- η experiment at Jefferson lab. The calorimeter was integrated into the data acquisition and trigger systems of the GlueX detector and used in the experiment to reconstruct Compton scattering events. The experiment started collecting data in the spring of 2019 and acquired about 30% of the required statistics. The calorimeter is a prototype for two PbWO 4 -based detectors: the Neutral Particle Spectrometer (NPS) and the lead tungstate insert of the Forward CALorimeter (FCAL) of the GlueX detector. The article presents the design and performance of the Compton calorimeter and gives a brief overview of the FCAL and NPS projects.

Silicon photomultipliers (SiPMs) are used in detectors of the GlueX experiment devoted to studying the nature of confinement. These detectors are operable at counting rates as high as 2 MHz with a time resolution (FWHM) of approximately 0.3 ns and a number of excited pixels of up to 104. For SiPMs that operate under these conditions, the measured dependences of the recovery time and the time resolution are presented as functions of the number of excited pixels and the excitation frequency. Using a picosecond laser, the time resolution has been measured for an array of 4 × 4 SiPMs, which was specially developed for the experiment.

An overview is presented of recent measurements of (i) proton and neutron scalar polarizabilities $\alpha_{E1}$ and $\beta_{M1}$, (ii) proton spin-polarizabilites $\gamma_{E1E1}$, $\gamma_{M1M1}$, $\gamma_{E1M2}$, and $\gamma_{M1E2}$, and (iii) charged and neutral pion scalar polarizabilities. The experiments completed, in progress, or in preparation are at Compass (CERN), HIGS, GlueX (JLab), Lund, and Mainz A2. These experiments span a range in beam energy from 100 MeV to 190 GeV, and target mass number from A=1 to 208

The JLab Eta Factory (JEF) program aims to use decays of the $\eta$ meson to study higher order terms in Chiral Pertubation theory, to determine the up-down quark mass ratio, and to probe for C-violating/P-conserving processes and other physics beyond the Standard Model. The program will take place at Jefferson Lab using the GlueX detector in Hall D. This article focuses on the rare $\eta\to\pi^0\gamma\gamma$ decay, which requires an upgrade to the existing forward calorimeter in the GlueX detector.

The GlueX forward calorimeter is an array of 2800 lead glass modules that was constructed to detect photons produced in the decays of hadrons. A background to this process originates from hadronic interactions in the calorimeter, which, in some instances, can be difficult to distinguish from low energy photon interactions. Machine learning techniques were applied to the classification of particle interactions in the GlueX forward calorimeter. The algorithms were trained on data using decays of the $\omega$ meson, which contain both true photons and charged particles that interact with the calorimeter. Algorithms were evaluated on efficiency, rate of false positives, run time, and implementation complexity. An algorithm that utilizes a multi-layer perceptron neural net was deployed in the GlueX software stack and provides a signal efficiency of 85% with a background rejection of 60% for an inclusive $\pi^0$ data sample for an intermediate quality constraint., Comment: 12 pages, 10 figures, submitted to JINST

We present measurements of the photon beam asymmetry Σ for the reaction γp → K+Σ0(1193) using the GlueX experiment in Jefferson Lab's Hall D. Data were collected using a linearly polarized photon beam with energy range 8.2-8.8 GeV incident on a liquid hydrogen target. Asymmetries are measured as functions of Mandelstam variables −t and −u. These are the first fully exclusive measurements of the photon beam asymmetry Σ in this reaction at high energies with detection of all final state particles. In the t-channel, results show that the reaction is dominated by the natural-parity exchange of presumably the K*(892) meson, as predicted by theoretical models. Results obtained for the u-channel are consistent with an intermediate baryon exchange mechanism predicted by theoretical models.

© 2020 IOP Publishing Ltd and Sissa Medialab. The GLUEX experiment is located in experimental Hall D at Jefferson Lab (JLab) and provides a unique capability to search for hybrid mesons in high-energy photoproduction, utilizing a ∼9 GeV linearly polarized photon beam. The initial, low-intensity phase of GLUEX was recently completed and a high-intensity phase has begun in 2020 which includes an upgraded kaon identification system, known as the DIRC (Detection of Internally Reflected Cherenkov light), utilizing components from the decommissioned BaBar DIRC. The identification of kaon final states will significantly enhance the GLUEX physics program, to aid in inferring the quark flavor content of conventional (and potentially hybrid) mesons. In these proceedings, we describe the installation of the GLUEX DIRC and the analysis of initial commissioning data.

The GlueX experiment is a photoproduction experiment located at Thomas Jefferson National Lab in Newport News, Virginia. GlueX is capable of making beam asymmetry (Σ) measurements using a tagged, linearly-polarized 9 GeV photon beam incident on a hydrogen target. Measurements of the beam asymmetry for the exclusive reactions γp → π0 p, γp → ηp and γp → η′p will provide insight into the meson production mechanisms. GlueX measurements are the first beam asymmetry results for the η and η′ in this energy range and are expected to further constrain Regge theory models for photoproduced pseudoscalar mesons. This talk will present preliminary results of the photon beam asymmetries as a function of the Mandelstam variable, t, for multiple η decay modes and the η′ → π+π− η decay mode.

The GlueX facility, featuring a linearly polarized 9 GeV real photon beam delivered to a large-acceptance detector system, has recently completed its first phase of running, and analysis efforts of this dataset are well underway. It has been suggested that at GlueX energies, quark systems beyond the three quark and quark-antiquark systems of baryons and mesons, such as hybrid mesons, tetraquarks and glueballs, should exist, and studies of these systems could shed new light on how quarks combine under the strong force, particularly the role played by gluons.GlueX data encompasses final states at energies where photoproduction of light scalar mesons, such as a0(980) and f0(980), can provide discriminatory evidence between various models, manifested in experimental observables such as the cross section and beam asymmetry, however many of these analyses comprise multi-particle final states, which can arise from numerous intermediate resonances formed via different production mechanisms.The work presented showcases efforts to measure the beam asymmetry of the reaction γp → pηπ, with a particular interest in future studies of the a0(980) meson, and discusses the application of longitudinal phase space plots, originally introduced by van Hove fifty years ago, as a means of optimizing event selection. This technique has found traction in several multi-particle final state analyses in GlueX, and provides an effective additional means of separately visualising meson and baryon production events with the same final state.

Understanding the nature of the baryon spectrum will provide useful insight in the non-perturbative regime of quantum chromodynamics. Significant progress has been made in the N* regime, but little is known about doubly-strange hyperons. Most knowledge of the Cascade baryons stems from kaon-nucleon experiments from the 1960s and 1970s or the more recent CLAS experiment at Jefferson Lab. This research studies doubly-strange baryons via photoproduction using the GlueX experiment at Jefferson Lab. The Cascade octet ground state Ξ− can be studied in exclusive t-channel production in the reaction γp → KY* → K+(Ξ−K+) with the subsequent decay of the Ξ− into Λπ−. The production model suggests the intermediate hyperon Y* is broad and possibly consists of overlapping states. With GlueX Phase-I data taking concluded, preliminary total cross section results of the Cascade ground state Ξ−(1320) are presented. An exploration into the reaction Ξ−* → K−Λ is also shown.

The Jefferson Lab 12GeV accelerator upgrade completed in 2015 is now producing data at volumes unprecedented for the lab. The resources required to process this data now exceed the capacity of the onsite farm necessitating the use of offsite computing resources for the first time in the history of JLab. GlueX is now utilizing NERSC for raw data production using the new SWIF2 workflow tool developed at JLab. In addition, simulation is being done on the OSG utilizing the same container and distributed file system technologies deployed for NERSC. Details of the workflow will be presented.

One of the most striking phenomenon of quantum chromodynamics (QCD) is the formation of the nucleon out of massless gluons and almost massless quarks. This system of confined quarks and gluons serves as the basic constituent of ordinary baryonic matter and exhibits the characteristic spectra of excited states, which are sensitive to the details of quark confinement. Complementary to nucleon structure studies in deep inelastic scattering experiments, nucleon excitations provide the unique opportunity to explore the many aspects of non-perturbative QCD. The last few years have seen significant progress toward the mapping of the nucleon spectrum. The rapidly growing database of high-quality experimental results on exclusive meson photo- and elec- troproduction on the nucleon from experimental facilities around the world now allows the hadron spectroscopy community to determine the scattering amplitudes of the underlying reactions more accurately and to identify nucleon resonance contributions with minimal model dependence. At Jefferson Laboratory (JLab), the excited baryon program now continues in the 12-GeV era with the successful data-taking of the GlueX experiment. Part of the GlueX scientific program is to search for and study the poorly-known multi-strange baryons which will provide an important missing link between the light- and the heavy-flavor baryons.

We report on the measurement of the beam asymmetry Σ for the reactions → γ p → p η and → γ p → p η ′ 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 Laboratory. 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 ′ in this energy range. We compare the results to theoretical predictions based on t -channel quasiparticle exchange. We also compare the ratio of Σ η to Σ η ′ to these models as this ratio is predicted to be sensitive to the amount of s ¯ s exchange in the production. We find that photoproduction of both η and η ′ is dominated by natural parity exchange with little dependence on − t .

The GlueX experiment, located in experimental Hall D of Jefferson Lab, seeks to map the spectrum of light mesons in search of exotic hybrid mesons, a predicted class of hadronic states with explicit gluonic degrees of freedom. GlueX is a photoproduction experiment utilizing a linearly polarized photon beam at $E_\gamma=$ 8-9 GeV and a large acceptance spectrometer. The experiment has already collected orders of magnitude more data than previous experiments at similar energies. We show results on asymmetry measurements in the production of pseudoscalars mesons, which refine our understanding of production mechanisms in photoproduction at our energies. We also present results on $J/\psi$ photoproduction, which provides model constraints on heavy quark photoproduction and the ability to search for s-channel production of pentaquark candidate $P_c^+$ states.

The GlueX experiment uses a tagged-photon beam produced by electrons from the 12 GeV CEBAF machine. The detector system is based on a 2 T solenoid and includes electro-magnetic calorimeters and drift chambers providing full acceptance coverage. The J/ψ particles are registered by their decay into e^+e^− pairs identified in the calorimeters. Taking advantage of the exclusivity of the reaction and the precise knowledge of the beam energy, we achieve a high mass resolution and a very low background, allowing us to perform a more sensitive unbinned analysis.

The Central Drift Chamber is a straw-tube wire chamber of cylindrical structure located surrounding the target inside the bore of the GlueX spectrometer solenoid. Its purpose is to detect and track charged particles with momenta as low as 0.25 GeV/c as well as to identify low-momentum protons via energy loss. The construction of the detector is described and its operation and calibration are discussed in detail. The design goal of 150 microns in position resolution has been reached., 27 pages, 17 figures

Quantum Chromodynamics (QCD) is the theory that describes how hadrons are built from quarks and gluons via the strong interaction. Many predictions have been experimentally confirmed, but others remain under experimental investigation. Of particular interest is how gluonic excitations give rise to states with constituent glue. One class of such states are hybrid mesons that are predicted by theoretical models and Lattice QCD calculations. Searching for and understanding the nature of these states is a primary physics goal of the GlueX experiment at the CEBAF accelerator at Jefferson Lab in the US. We will give an overview of the experiment, and present the status of the search for a hybrid meson candidate, Y (2175). This work is supported by HGS-HIRe., 5 pages, 6 figures, FAIRness 2019, submitted to Open Access Journal of Physics: Conference Series (JPCS)

We present preliminary results for the $J/\psi$ close-to-threshold photoproduction obtained in the GlueX experiment at Jefferson Lab. Close-to-threshold photoproduction $\gamma+p\rightarrow{}J/\psi+p$ probes small-size gluon configurations in the proton. This reaction may also contain a contribution from the s-channel production of the LHCb pentaquark $P(4450)\rightarrow{}J/\psi{}+p$ at beam energies of about 10 GeV. Measuring the size of the contribution allows to evaluate or put a limit on the branching ratio of the decay $P\rightarrow{}J/\psi+p$. The GlueX experiment is in the process of collecting data. The main research topic of the experiment is the spectroscopy of light mesons produced by a linearly polarized photon beam with the end point of about 12~GeV.

In the search for exotic mesons, the GlueX collaboration will soon extract moments of the $\eta\pi^0$ angular distribution. In the perspective of these results, we generalize the formalism of moment extraction to the case in which the two mesons are produced with a linearly polarized beam, and build a model for the reaction $\vec \gamma p \to \eta \pi^0 p$. The model includes resonant $S$-, $P$-, $D$-waves in $\eta\pi^0$, produced by natural exchanges. Moments of the $\eta\pi^0$ angular distribution are computed with and without the $P$-wave, to illustrate the sensitivity to exotic resonances. Although little sensitivity to the $P$-wave is found in moments of even angular momentum, moments of odd angular momentum are proportional to the interference between the $P$-wave and the dominant $S$- and $D$-waves. We also generalize the definition of the beam asymmetry for two mesons photoproduction and show that, when the meson momenta are perpendicular to the reaction plane, the beam asymmetry enhances the sensitivity to the exotic $P$-wave., Comment: 17 pages, 7 figures, match the published version

We update our previous calculation of $J/\ensuremath{\psi}$ photoproduction near threshold [Y. Hatta and D. L. Yang, Phys. Rev. D 98, 074003 (2018)] by incorporating the recent developments in theory and the new experimental data from Ali et al. [the GlueX Collaboration] at Jefferson Laboratory. We then propose to study the near threshold production of $\mathrm{\ensuremath{\Upsilon}}$ and $J/\ensuremath{\psi}$ in ultraperipheral $pA$ collisions at RHIC. These processes are sensitive to the gluon condensate in the proton which is related to the proton mass via the QCD trace anomaly. Our result emphasizes the role of gluons in generating the proton mass.