Bulletin of the American Physical Society
APS April Meeting 2019
Volume 64, Number 3
Saturday–Tuesday, April 13–16, 2019; Denver, Colorado
Session J05: Early Results From JLab 12 GeVInvited
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Sponsoring Units: DNP Chair: Julie Roche, Ohio University Room: Sheraton Governor's Square 14 |
Sunday, April 14, 2019 1:30PM - 2:06PM |
J05.00001: First results from the MARATHON Jefferson Lab Tritium DIS Experiment Invited Speaker: Gerassimos G Petratos Preliminary results from a Jefferson Lab (JLab) experiment on electron deep inelastic scattering (DIS) from the 3H and 3He mirror nuclei will be presented. The experiment (MARATHON, “MeAsurement of the F2n/F2p, d/u RAtios and A=3 EMC Effect in Deep Inelastic Electron Scattering Off the Tritium and Helium MirrOr Nuclei”) took data for 70 days in the period January-April 2018 in the Hall A Facility of JLab, using an 11 GeV electron beam, two High Resolution Spectrometers, and a high-pressure 2H/3H/3He target system. The experiment has measured DIS cross section ratios for 2H, 3H and 3He. It will determine, using a new novel method, free of theoretical uncertainties present in previous SLAC measurements, the ratio of the F2n/F2p structure functions of the neutron and proton, and extract the d/u ratio of the up and down quark probability distributions in the proton. The results from the experiment are expected to test predictions of the quark model of the nucleon and of perturbative quantum chromodynamics, and to constrain the nucleon’s parton distribution function parametrizations needed for the interpretation of high energy collider data. The experiment will also determine precisely the EMC effect of the two A=3 mirror nuclei. The results are considered essential for the explanation of the EMC effect, which describes the modification of the nucleon structure functions in the nuclear medium. |
Sunday, April 14, 2019 2:06PM - 2:42PM |
J05.00002: Recent Results From GlueX Invited Speaker: Colin Gleason The primary goal of the GlueX experiment at Jefferson Lab is to search for and map the spectrum of light hybrid mesons. GlueX began taking data in 2016 and in December 2018 completed its initial program of data collection, providing orders of magnitude more data than similar experiments at this energy. As a first step in developing it's analysis program to search for hybrid mesons, the GlueX Collaboration aims to measure polarization observables, spin density matrix elements (SDMEs), and cross-sections of mesons in order to understand their production mechanism. This talk will give an overview of recent results from GlueX, including beam asymmetries and SDMEs, current efforts to study light mesons through amplitude analysis, discuss the prospects for hybrid meson searches, and report on other measurements such as the cross-section of J/ψ at threshold. |
Sunday, April 14, 2019 2:42PM - 3:18PM |
J05.00003: CLAS12 First Experiments and Hadron Structure Invited Speaker: Daniel S Carman The new CLAS12 large acceptance spectrometer was recently installed in Hall B as part of the 12 GeV upgrade project at Jefferson Laboratory that served to double the maximum electron beam energy of the accelerator. The approved CLAS12 experimental physics program spans a broad scientific scope designed to address fundamental and critical issues in nuclear physics such as detailed spectroscopy of the excited baryon spectrum including a search for hybrid baryons where the glue serves as an active structural component, elucidation of the role of gluons in hadronic structure, studies of the implications of short range forces acting in nucleons and nuclei, and detailed investigations that serve to reveal the structure of ground and excited states including 3-D imaging of the ground state nucleons and exploration of the N --> N* form factors in the transition from the regimes of confinement to perturbative QCD. These studies will address questions on the nature of the mass of hadrons, quark-gluon confinement, and how such a diversity of hadrons emerges from QCD. The commissioning of the CLAS12 spectrometer was completed during an Engineering Run that took place in Dec. 2017 and Jan. 2018. This was followed by the first physics production running periods spanning 23 weeks in the spring and fall of 2018. This talk will review the initial CLAS12 physics program and highlight the current status of the ongoing physics analyses. |
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