Bulletin of the American Physical Society
APS April Meeting 2019
Volume 64, Number 3
Saturday–Tuesday, April 13–16, 2019; Denver, Colorado
Session D09: Meson Electro- and Photo-production |
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Sponsoring Units: DNP GHP Chair: Latifa Elouadrhiri, Jefferson Lab Room: Sheraton Governor's Square 11 |
Saturday, April 13, 2019 3:30PM - 3:42PM |
D09.00001: A Search for the LHCb Pentaquark in Hall C at Jefferson Lab Burcu Duran The Jefferson Lab experiment E12-16-007 will measure the elastic J/ψ photo-production cross section as a function of proton momentum transfer variable t and photon energy Eγ in the region of the recently discovered LHCb charmed pentaquark Pc(4380) and Pc(4450) resonances. The experiment will be performed using a bremsstrahlung beam generated by a 10.6 GeV incident electron beam traversing a copper radiator upstream of a hydrogen target in Hall C. The two high momentum spectrometers of Hall C, HMS and SHMS will detect the e+e- di-lepton J/ψ decay pair in coincidence. In combination with the high incident photon flux, the optimized spectrometer settings provide the preferred kinematics where the s-channel pentaquark signal, if it exists, should strongly dominate over that of the regular t-channel J/ψ production. I will discuss the very preliminary results that will either confirm or refute the resonance nature of the LHCb pentaquark Pc(4450). |
Saturday, April 13, 2019 3:42PM - 3:54PM |
D09.00002: Onset of the Color Transparency (CT) in Protons at 12 GeV in Hall C at Jefferson Lab (JLab) Deepak K Bhetuwal CT is a unique prediction of QCD where the final (and/or initial) state interactions of hadrons with the nuclear medium are suppressed for exclusive processes at high momentum transfers. While this phenomenon has been observed for mesons, there has never been a conclusive observation for baryons. A clear signal of CT for baryons would be the first evidence of baryons fluctuating to a small size in the nucleus, and the onset would show the transition from partonic picture to quark-gluon degrees of freedom. The experiment E12-06-107 searching for the onset of CT in protons, was completed in Hall C at JLab using the recently upgraded 12 GeV e- beam. It used HMS and new SHMS spectrometers in coincidence to measure the 12C(e,e’p) proton knockout reaction. Data were collected on a 12C target over the range of Q2 = 8 – 14.3 (GeV/c)2 covering the region where a previous A(p,2p) experiment at BNL had observed an enhancement. Additional data on a 1H target were collected to determine the elementary process. A rise in the Proton Transparency (PT) as a function of Q2 is predicted to be a signature of the onset of CT. This talk will summarize the status of the analysis and present preliminary results on hydrogen normalization and nuclear transparency. |
Saturday, April 13, 2019 3:54PM - 4:06PM |
D09.00003: CLAS12 at Jefferson Lab - Instrumentation and Performances Latifa Elouadrhiri The CEBAF Large Acceptance Spectrometer (CLAS12) is a state-of-the-art particle detector designed and built as part of the Jefferson Lab 12GeV Upgrade to map out distributions of quarks in space and momentum, culminating in a picture the internal structure of protons and neutrons. An international collaboration has designed fabricated, assembled, and commissioned CLAS12 in Hall B at Jefferson Lab. The CLAS12 detector is based on a combination of a 6-coils toroidal magnet and a high field solenoid magnet. The combined magnetic fields provide a large coverage in both azimuthal and polar angles. Trajectory reconstruction is provided using drift chambers at forward angles and silicon detectors at large angles Cherenkov counters, time-of-Flight systems and calorimeters provide good particle identification for electrons, charged pions, kaons and protons. Fast triggering and high data acquisition rates allow operation at luminosities of 10^35/cm^2/s. These capabilities are being used in a broad scientific program to study the structure and interactions of baryons, meson and nuclei using polarized and unpolarized targets. We will present general description of the design, construction and performance of CLAS12 enabling a new generation of experiments in hadronic physics. |
Saturday, April 13, 2019 4:06PM - 4:18PM |
D09.00004: The Search for Color Transparency at 12 GeV at JLab John Matter Color Transparency (CT) is a prediction of QCD that at high momentum transfer $Q^2$, a system of quarks, each of which would normally interact strongly with nuclear matter, could form a small color-neutral object whose compact transverse size would be maintained for some distance, passing through the nucleus undisturbed. A clear signature of CT would be a dramatic rise in nuclear transparency $T$ with increasing $Q^2$. The existence of CT would contradict traditional Glauber multiple scattering theory in its domain of validity, which predicts constant $T$. CT is a prerequisite to the validity of QCD factorization theorems, which provide access to the generalized parton distributions that contain information about the transverse and angular momenta carried by quarks in nucleons. The E12-06-107 experiment at JLab measured $T$ in quasielastic electron-proton scattering with carbon-12 and liquid hydrogen targets, for $Q^2$ between 8 and 14.3 $GeV^2$, a range over which $T$ should differ appreciably from Glauber calculations. |
Saturday, April 13, 2019 4:18PM - 4:30PM |
D09.00005: Determining the unknown Λ-n interaction by investigating the Λnn resonance Bishnu D Pandey Abstract We carried out the experiment E12-17-003 at Jefferson Lab in November 2018 by using the 3H(e,e’K+)Λnn reaction with the high quality CEBAF electron beam and the Hall A high resolution spectrometers. The goal of the experiment is to search for the possible Λnn three-body resonance. If such a resonance exists, it may provide, for the first time, experimental information that can be used to determine the unknown Λn interaction relative to the Λp interaction fitted from limited Λp scattering data. This can help to address the long existing puzzle of Charge-symmetry-breaking (CSB) in ΛN interactions.
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Saturday, April 13, 2019 4:30PM - 4:42PM |
D09.00006: Equivalency of Isospin and Particle Representations for NN{\bar K} Kaonic Clusters Igor Filikhine, Roman Ya Kezerashvili, Vladimir M Suslov, Branislav Vlahovic In the framework of the Faddeev equations in configuration space the quasi-bound states of the kaonic cluster NN{\bar K} are considered using both the isospin and particle representations. Within the isospin formalism, the '' ppK- '' cluster is determined as NN{\bar K}(sNN=0) system (the other possible cluster is " dK- ''). The alternative consideration of the kaonic clusters which was recently proposed (PRC 94, 054001-7 (2016)) is the isospinless ''particle model''. In this model, the system is presented as superposition of the ppK- and pnK0 states which are possible due to a particle transition. We show the equivalency of isospin and particle representations using an unitary transformation of isospin basis. Such equivalency is possible under the assumption that the probabilities to find the system in the ppK- or pnK0 state are equal. Numerical calculations using phenomenological potentials are presented for the case of weak coupling of the channels. The relation of the particle representation to the theory of two-level system is addressed and discussed.
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Saturday, April 13, 2019 4:42PM - 4:54PM |
D09.00007: A study of Lambda-Nucleon scattering using the CLAS detector Joseph Rowley, Kenneth H Hicks, John W Price Previous data for the elastic scattering of Lambda baryons from the nucleon |
Saturday, April 13, 2019 4:54PM - 5:06PM |
D09.00008: The reaction n p -> d π0 measured at CLAS as a probe of Nucleon-Delta Attraction Kenneth H Hicks, Nicholas Compton The CLAS detector setup, previously located in Hall B of Jefferson Lab, has been used to investigate secondary scattering reactions. In the first step, neutrons are produced via the photoproduction reaction γ p -> π+ n, which is tagged via detection of the π+ in CLAS. The neutrons then propagate through the 40-cm long liquid hydrogen target, and some of these neutrons undergo a secondary scattering reaction. The exclusive reaction n p -> d π0 is seen via detection of a deuteron in CLAS, coincident with the tagged π+. Cross sections from this reaction show a resonant peaking at a center-of-mass energy, W, corresponding to a resonant nucleon-delta system, which decays to a bound deuteron and a neutral pion. These data provide new information that can be used to extract details of the nuclear force in the N-Δ system. |
Saturday, April 13, 2019 5:06PM - 5:18PM |
D09.00009: Photoproduction of Λ* resonances at CLAS Utsav Shrestha, Taya N 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 partial wave analysis, which will be necessary to resolve the individual cross sections for these two resonances, will be outlined. |
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