Bulletin of the American Physical Society
2019 Fall Meeting of the APS Division of Nuclear Physics
Volume 64, Number 12
Monday–Thursday, October 14–17, 2019; Crystal City, Virginia
Session KM: Electromagnetic Interactions II |
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Chair: Ken Hicks, Ohio University Room: Salon J |
Wednesday, October 16, 2019 8:30AM - 8:42AM |
KM.00001: ABSTRACT WITHDRAWN |
Wednesday, October 16, 2019 8:42AM - 8:54AM |
KM.00002: Exclusive Eta and Eta’ Photoproduction and Beam Asymmetries at GlueX Will McGinley, Tegan Beattie, Zisis Papandreou, Curtis Meyer, Justin Stevens, Dave Mack The GlueX experiment is a photoproduction experiment located at Thomas Jefferson National Accelerator Facility (TJNAF) in Newport News, Virginia. GlueX is capable of making beam asymmetry ($\Sigma$) measurements using a tagged, linearly-polarized 9 GeV photon beam incident on a hydrogen target. Measurements of the beam asymmetry for the exclusive reactions, $\gamma p\rightarrow\eta p$ and $\gamma p\rightarrow\eta'p$, will provide insight into the meson production mechanisms. GlueX measurements are the first beam asymmetry results for the $\eta$ and $\eta^{\prime}$ in this energy range and are expected to further constrain Regge theory models for photoproduced pseudoscalar mesons. This talk will present results of the photon beam asymmetries as a function of the Mandelstam variable, t , for multiple $\eta$ decay modes and the $\eta'\rightarrow\pi^+\pi^-\eta$ decay mode. [Preview Abstract] |
Wednesday, October 16, 2019 8:54AM - 9:06AM |
KM.00003: Analysis of $K^* K$ states photoproduced from the proton Sebastian Cole No comprehensive theoretical description of hadronic matter can be achieved without a solid knowledge of the excited meson states. Of particular interest are the "exotic" states that can not be described by the constituent quark model. The meson spectrum decaying into $K^* K$ may contain such an exotic in the form of a hybrid-meson state, where a gluon has been promoted to being a real constituent. However, while the meson spectrum decaying into $K^* K$ may prove very useful in understanding hadronic matter, that spectrum has not been fully explored. Jefferson Lab data from the GlueX collaboration for the $\gamma p \rightarrow p K^* K$ reactions have been taken using a linearly polarized photon beam with energies of about 9 GeV at the coherent edge. Preliminary results of the $K^* K$ meson spectrum will be presented. [Preview Abstract] |
Wednesday, October 16, 2019 9:06AM - 9:18AM |
KM.00004: ABSTRACT WITHDRAWN |
Wednesday, October 16, 2019 9:18AM - 9:30AM |
KM.00005: Studies of the $\omega\pi\pi$ Final State at GlueX Amy Schertz Signals for exotic mesons, which have quantum numbers that aren't allowed for a quark-antiquark pair, have been experimentally observed, but their exact nature is still unknown. A candidate for these exotics is the hybrid meson, which consists of a quark, an antiquark, and an excited gluon. GlueX, a photoproduction experiment in Jefferson Lab's Hall D, aims to map the spectrum of light quark mesons by studying a multitude of final states allowed by the detector's large acceptance. Evidence for the lightest expected exotic hybrid meson has been shown in a partial wave analysis by the BNL E852 experiment of the $\omega\pi\pi$ final state in pion production. In this talk, studies of the reaction $\gamma p \rightarrow \omega\pi\pi p$ at GlueX will be presented. [Preview Abstract] |
Wednesday, October 16, 2019 9:30AM - 9:42AM |
KM.00006: The GlueX DIRC upgrade and its utilization in the upcoming high intensity experiments Andrew Hurley The GlueX experiment is a photoproduction experiment located in Hall D at Jefferson Lab (JLab). GlueX uses the 12 GeV electron beam from the Jlab accelerator to produce a 9 GeV, linear polarized photon beam that is incident on a stationary target. The primary goal of the GlueX experiment is to study the hadronic spectrum, especially states with gluonic excitation (hybrids) and other states that exist outside the quark model. With the completion of data taking for the initial low intensity phase of the GlueX in 2018, the detector has undergone upgrades in preparation for the high-intensity phase which begins in Fall 2019. One of these upgrades is the inclusion of a new PID detector known as the DIRC (Detection of Internally Reflected Cherenkov light). The GlueX DIRC is designed to aid in the separation of kaons from pions in order to improve the experiment’s ability to study the hadronic spectrum in states with strange quark content. This talk will give an overview of the installation and commissioning of the GlueX DIRC, as well as some examples of analyses that will make use of the GlueX DIRC’s kaon-pion separation power. [Preview Abstract] |
Wednesday, October 16, 2019 9:42AM - 9:54AM |
KM.00007: Beam Asymmetries for Eta Pi Photoproduction on the Proton at GlueX Stuart Fegan The GlueX facility, featuring a linearly polarised 9 GeV real photon beam delivered to a large-acceptance detector system, recently completed an initial phase of data taking at energies where quark systems beyond the known baryons and mesons, such as hybrid mesons, tetraquarks and glueballs, should exist. Analysis efforts are well underway, and results are expected to shed new light on how quarks combine under the strong force, particularly the role played by gluons. The work presented showcases efforts to measure beam asymmetries in the reaction $\gamma p\rightarrow p\eta\pi$, where both mesons decay to two photons, and whose invariant mass spectrum features both the $a_0(980)$ meson and a nearby signal from $a_2(1320)$. The beam asymmetry of the $\eta\pi$ system can be used to search for exotic signals, for instance through the presence of a non-zero P-wave contribution, which may be seen in asymmetry measurements at small opening angles in the meson decay frame. Additionally, the t-dependence of the $a_0(980)$ beam asymmetry can provide insight into production mechanisms of this state. Future prospects for related analyses in this reaction topology, informed by these measurements, will also be discussed. [Preview Abstract] |
Wednesday, October 16, 2019 9:54AM - 10:06AM |
KM.00008: PrimEx-Eta: A Precision Measurement of the Eta Meson Radiative Decay Width Andrew Smith The $\eta$ meson is a unique probe of QCD symmetry breaking. Of particular importance is the $\eta\rightarrow\gamma\gamma$ decay, as it proceeds via the chiral anomaly. In the chiral limit, the amplitude for the two-photon decay of the pure SU(3) states, $\eta_{0}$ and $\eta_{8}$, is exactly calculable, and therefore a precision measurement of the $\eta$ radiative decay width provides both a precision test of this chiral anomaly prediction as well as information about the $\eta$-$\eta'$ mixing angle. In the past, this 2$\gamma$ decay width has been measured both in a fixed target experiment utilizing the Primakoff effect and in $e^{+}e^{-}$ collider experiments. However, a large discrepancy between the results of the two types of experiments remains unresolved. The PrimEx-$\eta$ experiment in Hall D at Jefferson Lab will perform a precision measurement of $\Gamma_{\eta\rightarrow\gamma\gamma}$ via the Primakoff method to address this discrepancy, and to reduce the overall uncertainty. Additionally, it will allow to significantly reduce uncertainties on partial widths for all other $\eta$ decays. In this talk the motivation and experimental techniques will be discussed along with a presentation of data from the experiment's first phase which was completed in the Spring of 2019. [Preview Abstract] |
Wednesday, October 16, 2019 10:06AM - 10:18AM |
KM.00009: Search for the onset of Color Transparency in Protons Deepak Bhetuwal Color transparency (CT) is a a unique prediction of Quantum Chromodynamics (QCD) where the final (and/or initial) state interactions of hadrons with the nuclear medium are suppressed for exclusive processes at high momentum transfers. During the spring of 2018, the experiment E1206107 to measure the Proton Transparency was the first to run in Hall C at Jefferson Lab using the upgraded 12 GeV electron beam. Our experiment used the High Momentum Spectrometer (HMS) and new Super High Momentum Spectrometer (SHMS) in coincidence to measure ${^1^2}$C(e,e p) proton knockout to extract the proton nuclear transparency with additional 1H measurements to determine the elementary process, over the range Q${^2}$ = 8 $-$ 14.3 (GeV/c)${^2}$ . A rise in the proton transparency as a function of Q${^2}$ is predicted to be a signature of the onset of Color Transparency. This talk will summarize the status of the experiment since the completion of data taking and show some preliminary results. [Preview Abstract] |
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