Bulletin of the American Physical Society
5th Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Volume 63, Number 12
Tuesday–Saturday, October 23–27, 2018; Waikoloa, Hawaii
Session EE: Mini-symposium: Photoproduction and Electroproduction of Hadrons I |
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Chair: Ken Hicks, Ohio University Room: Hilton King's 1 |
Thursday, October 25, 2018 7:00PM - 7:30PM |
EE.00001: Advances in the studies of the nucleon resonance spectrum in experiments with electromagnetic probes. Invited Speaker: Victor Mokeev The studies of the nucleon resonance spectrum with the focus on the search for new baryon states for a long time remain the challenging topic in hadron physics. Full resonance spectrum plays a critical role in the evolution of ~ millisecond age Universe in the transition from the quark-gluon to the hadron gas phases. Recent LQCD evaluations of the N*-spectrum from the first QCD principles suggest existence as much new nucleon resonances as expected in the quark models employed SU(6)*O(3) symmetry. Discovery of several new nucleon resonances in the global analyses of exclusive meson photoproduction off protons data with decisive impact from the CLAS measurements of exclusive KY photoproduction will be presented. Combined studies of charged double pion photo- and electroproduction data from CLAS revealed strong evidence for another N'(1720)3/2+ new baryon state. The information on electroexcitation amplitudes of this state has become available for the first time offering the insight to the new baryon state structure. The prospects for the search of the new states of baryon matter with glue as the structural component in the experiments with the CLAS12 detector will be outlined. |
Thursday, October 25, 2018 7:30PM - 7:45PM |
EE.00002: GW Progress in Neutron Couplings Igor I Strakovsky, William J Briscoe An overview of the GW SAID group effort to analyze pion photoproduction on the neutron-target will be given. The disentangling of the isoscalar and isovector EM couplings of N∗ and Δ∗ resonances does require compatible data on both proton and neutron targets. The final-state interactions play a critical role in the state-of-the-art analysis in extraction of the γn → πN data from the deuteron target experiments. The new data help to constrain coupled-channel analysis fits used to disentangle the spectrum of N* resonances and extract their properties. Photon decay amplitudes N*àgamma+ n at the resonance poles will be determined. The neutron program is an important component of the current JLab, MAMI-C, SPring-8, ELSA, and ELPH studies. |
Thursday, October 25, 2018 7:45PM - 8:00PM |
EE.00003: Impact of CLAS meson photoproduction experiments on N* spectroscopy Eugene Pasyuk When the first nucleon resonance, Δ, was observed in pion-nucleon scattering in 1952, the nucleon resonance era begun Almost seven decades later the latest edition of the Review of the Particle Physics lists 50 non-strange baryons. Nonetheless, models consistently predict still more states yet to be observed - the so-called "missing resonance problem". Until the mid 90s, of the twentieth century most of the data on the nucleon resonances came from pion-nucleon scattering. However over the last two decades the focus has shifted to exclusive meson photoproduction experiments as the main source of new information about nucleon excitations. The CEBAF Large Acceptance Spectrometer, CLAS, emerged as the major contributors to this field. An overview of CLAS photoproduction experiments will be presented and their impact on N* spectroscopy will be discussed. |
Thursday, October 25, 2018 8:00PM - 8:15PM |
EE.00004: Photoproduction of light mesons at SPring-8 LEPS2/BGOegg experiments Norihito Muramatsu, Toshikazu Hashimoto, Tran Nam A photon beam with high linear polarization is available in the tagged energy range of 1.3¾2.4 GeV at the SPring-8 LEPS2 beamline. Large statistics data of hadron photoproduction have been collected at the LEPS2/BGOegg experiments by using a liquid hydrogen target, which is surrounded by a large acceptance electromagnetic calorimeter and charged particle detectors. The electromagnetic calorimeter consists of 1,320 BGO crystals, assembled in the "egg" shape covering the polar angle range of 24¾144 degrees. The reactions of γp ® π0p, γp ® ηp, and γp ® ωp have been analyzed in the meson decay modes of π0 / η ® γγ and ω ® π0γ. We measured the differential cross sections and photon beam asymmetries of these photoproduction processes to study baryon resonances. New experimental results will be shown, including the high energy region where the photon beam asymmetries had not been measured. |
Thursday, October 25, 2018 8:15PM - 8:30PM |
EE.00005: First Studies of Exclusive Reactions in the Resonance Region with CLAS12 Stefan Diehl, Kyungseon Joo The CLAS12 detector started data taking with a polarized 10.6-GeV electron beam at Jefferson Laboratory (JLab) this February. The N* program of CLAS12 is focussed on the study of the structure of excited nucleon states for the still unexplored regions of photon virtualities Q² down to 0.05 GeV² and for Q² from 5 – 12 GeV². The focus at low Q² is the search for new so-called hybrid baryon states. At high Q², CLAS12 will map out the N* core quark structure at distances where the transition from quark gluon confinement to pQCD takes place. The talk will focus on the first measurements of the different exclusive reactions with CLAS12. A special focus will be on the exclusive ep→epπ0 channel and the semi-inclusive ep→eπ0X production. For the exclusive channel, the beam spin asymmetry will be studied in the resonance region. These processes can be seen as a benchmark for the capabilities of CLAS12. In addition, the measurement and characterization of the Φ(1020) and Λ(1520) in the exclusive channel ep→epK+K- will be presented. For the Λ(1520), the first results for the beam-spin asymmetry will be shown. |
Thursday, October 25, 2018 8:30PM - 8:45PM |
EE.00006: Structures of the Λ(1405) in the Skyrme model Takashi Ezoe, Atsushi Hosaka The Λ(1405) is well-known as a candidate of an exotic hadron resonance. Historically, the Λ(1405) was identified with a bound state of the anti-kaon (Kbar) and the nucleon (N). However, it is now considered to be a resonance state of the KbarN and πΣ channels. There are many experimental and theoretical studies for the Λ(1405). In this talk, we have investigated the structures of the Λ(1405) in the Skyrme model, where a baryon is described by a soliton with finite structures. To do that, we derive the coupling constant for the KbarN-πΣ vertex. |
Thursday, October 25, 2018 8:45PM - 9:00PM |
EE.00007: First Measurements of Inclusive Electron Scattering off Protons with CLAS12 Nikolay Markov The first physics run with the new CLAS12 spectrometer in Hall B at Jefferson Laboratory has recently been completed. The data was taken with a 10.6-GeV longitudinally polarized electron beam on an unpolarized liquid-hydrogen target. The phase space covered by CLAS12 spans a wide kinematic range in W up to 4 GeV and Q2 up to 10-12 GeV2. These data offer new opportunities in the exploration of inclusive, semi-inclusive, and fully exclusive reactions covering a host of different physics topics. I will present initial results for one of the initial studies with the first CLAS12 data set aimed at the measurements of the inclusive electroproduction cross sections. I will also report measurements of the elastic electron-scattering cross section at a beam energy of 2.2 GeV. Comparison of the inclusive and elastic cross sections from CLAS12 with the available world data is essential for the understanding and validation of the CLAS12 performance. The inclusive electron-scattering cross sections from this study will provide the first data in the resonance region at high photon virtualities Q2 > 5.0 GeV2. |
Thursday, October 25, 2018 9:00PM - 9:15PM |
EE.00008: A study of the γp -> K+Λ* reaction Utsav Shrestha, Taya Chetry, Kenneth H Hicks Much is known about the photoproduction of the hyperon resonances Λ(1405)1/2- and Λ(1520)3/2-, but little is known about photoproduction to the higher-mass resonances Λ(1670)1/2- and Λ(1690)3/2-. Both pairs of resonances are spin-orbit partners and are rated as 4-star (well-known) by the Particle Data Group. In the quark model, the Λ(1405) and Λ(1520) resonances are assigned to the SU(3) singlet, where the Λ(1670) and Λ(1690) are assigned to the octet. In this presentation, we will present a first look at photoproduction data for these hyperon octet resonances using data from the CLAS detector at Jefferson Lab. Future plans for a partial wave analysis, which will be necessary to resolve the individual cross sections for these two resonances, will be outlined. |
Thursday, October 25, 2018 9:15PM - 9:30PM |
EE.00009: A Study of the γd->π+π-d Reaction using CLAS at JLab Taya N Chetry, Kenneth H Hicks, Reinhard A Schumacher This study investigates a recently-observed NΔ (d*) resonance decaying to the πd final state using CLAS at Jefferson Lab, Virginia. Tagged photons with beam energies between 0.8 and 3.6 GeV were produced using the Bremsstrahlung process incident on a liquid deuterium target. The final state particles detected were an energetic deuteron and two oppositely charged pions. The peak of the resonance-like structure is at about 2150 MeV. The possible d* resonance has been seen in two CLAS datasets1. Partial-wave analysis of pion-deuteron scattering has also shown a resonance at a mass of about 2145 MeV in the 1D2 partial wave. A preliminary differential cross section measurement of this possible resonance will be presented.
1R. Schumacher, YITP workshop MIN16 "Meson in Nucleus 2016", Kyoto University. |
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