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 GH: Electromagnetic Interactions I |
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Chair: Daniel Carman, Jefferson Laboratory Room: Salon B |
Tuesday, October 15, 2019 2:00PM - 2:12PM |
GH.00001: Helicity Asymmetry $ E $ for $\gamma p \to \pi^0 p$ from JLAB CLAS g9a/FROST dataset with application of Machine Learning Chan Wook Kim In pursuit of resolving the problem of missing baryon resonances, the measurement of the double polarization observable E for $\gamma p\to\pi^0 p $ was performed using a circularly polarized photon beam on longitudinally polarized proton target (FROzen Spin Target experiment) at $ W $ energies between 1450 MeV and 2050 MeV. The final state particles were detected with CEBAF Large Acceptance Spectrometer (CLAS) in Hall B at the Thomas Jefferson National Accelerator Facility. During analysis of the CLAS g9a/FROST data, various types of deep neural networks were tested and employed to control the effects of hydrogen contamination on carbon targets which emerged while polarizing nearby butanol targets via Dynamic Nuclear Polarization technique. The extracted data of helicity asymmetry E will be compared to the SAID, MAID and BnGa partial wave analysis predictions and included to GW SAID database to further investigate missing resonances. \\ In this talk, preliminary results of extracted helicity asymmetry E for $ \gamma p \to \pi^0 p $ and applications of machine learning techniques will be presented. [Preview Abstract] |
Tuesday, October 15, 2019 2:12PM - 2:24PM |
GH.00002: TDA measurements based on hard excusive pion electroproduction with CLAS at JLAB Stefan Diehl Many experiments showed the QCD factorisation mechanism in the "nearly forward region" (large Q\texttwosuperior and small \textbar t\textbar ) can be divided into a hard part, described by perturbative QCD (pQCD) and in two general structure functions, the GPDs for the nucleon and the pion distribution amplitudes (DAs). The recent measurement from CLAS in the "nearly backward" kinematic region (large Q\texttwosuperior and small \textbar u\textbar ) provided the potentially applicable collinear factorized description in terms of a convolution of the non-perturbative nucleon to-pion transitions (TDAs), the nucleon DAs and the hard interaction amplitude from pQCD. For the first time, we have measured single beam spin asymmetries to extract A$_{\mathrm{LU}}^{\mathrm{sin(\phi )\thinspace }}$moments from the hard exclusive $\pi^{\mathrm{+}}$ channel off the unpolarized hydrogen target in a wide range of kinematics from forward to backw. angles in CM frame. The measured moment in forward angles is known to be sensitive to generalized parton distributions (GPDs), while in backward angles, it is known to be sensitive to transition distribution amplitudes (TDAs). Our results clearly show that the sign of forward beam spin asymmetry measurements is positive whereas that of backward BSA measurements is negative, with the sign transition taking place around 90\textdegree . By performing accurate measurements over a wide range of Q\texttwosuperior , x$_{\mathrm{B}}$ and -t, we can explore the transition from hadronic to partonic reaction mechanisms. As an Outlook, first results on the exclusive pion electroproduction with CLAS12 will be presented. [Preview Abstract] |
Tuesday, October 15, 2019 2:24PM - 2:36PM |
GH.00003: Dihadron Beam Spin Asymmetries and Helicity-Dependent Fragmentation in SIDIS at CLAS Christopher Dilks Dihadron production in Semi-Inclusive Deep Inelastic Scattering (SIDIS) provides unprecedented access to hadron structure and to spin-orbit correlations in hadronization. Beam spin asymmetry measurements in dihadron production are sensitive to twist-3 collinear PDFs as well as dihadron fragmentation functions. In particular, the dihadron fragmentation function $G_1^{\perp}$ has not yet been experimentally constrained, and describes the correlation of the fragmenting quark helicity with azimuthal angles of the hadron pair. The quark-jet hadronization model predicts a sizeable $G_1^{\perp}$ and assumes a longitudinally polarized fragmenting quark recoils and acquires nonzero transverse polarization via a wormgear-type splitting. Measuring beam spin asymmetry modulations in various production channels, including charged and neutral pions as well as kaons, will probe the flavor dependence of $G_1^{\perp}$ and other relevant distributions. Progress on the beam spin asymmetry measurements in dihadron production from electron-proton scattering at CLAS will be shown, and their potential impact on $G_1^{\perp}$ extractions will be discussed. [Preview Abstract] |
Tuesday, October 15, 2019 2:36PM - 2:48PM |
GH.00004: Photoproduction of $\Lambda^*$ at CLAS Utsav Shrestha, Kenneth Hicks Much is known about the photoproduction of the hyperon resonances $\Lambda(1405)1/2^-$ and $\Lambda(1520)3/2^-$, but little is known about photoproduction to the higher-mass resonances $\Lambda(1670)1/2^-$ and $\Lambda(1690)3/2^-$. 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 $\Lambda(1405)$ and $\Lambda(1520)$ resonances are assigned to the SU(3) singlet, where the $\Lambda(1670)$ and $\Lambda(1690)$ are assigned to the octet. In this presentation, we will present differential cross sections for $\Lambda(1520)3/2^-$ and preliminary look at the two hyperon octet resonances using the photoproduction 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. [Preview Abstract] |
Tuesday, October 15, 2019 2:48PM - 3:00PM |
GH.00005: A Study of Lambda-Nucleon scattering using the CLAS detector Joseph Rowley, Ken Hicks Elastic scattering of Lambda baryons with protons is important to know, in part because these reactions might take place in the center of a neutron stars. Current $\Lambda N$ elastic scattering data comes primarily from bubble chamber experiments. The richness of $\Lambda$ production in modern day accelerators has thus never been realized. $\Lambda N$ data is very limited compared to other elastic scattering processes, such as $NN$, $KN$ and $\pi N$. Data was mined from existing experiments from the g12 run of the CLAS detector in Hall B of Jefferson Lab. A high luminosity photon beam incident on a 40 cm liquid hydrogen target allows for a $\Lambda$ beam to be created inside the target. We look at the reaction $\gamma p \rightarrow K^+ \Lambda$ to generate the $\Lambda$ beam. The created $\Lambda$ then proceeded to scatter elastically with a second proton in the target. The $K^+ \Lambda$ cross section is well known, which allows us to determine the flux of the $\Lambda$ beam. From this, preliminary results for the $\Lambda N$ cross section will be presented along with new data for its angular distribution. [Preview Abstract] |
Tuesday, October 15, 2019 3:00PM - 3:12PM |
GH.00006: Study of $\Lambda$ Hyperon Fragmentation in Current and Target Regions using CLAS Taya Chetry, Lamiaa El Fassi The color propagation and hadron production from hard interactions in nuclei have been extensively studied over the last few decades. These studies are related to one of the basic phenomena of quantum chromodynamics (QCD) dubbed as hadronization or fragmentation. In this process, an energetic struck quark transforms to color-neutral hadrons making it an effective probe of the confinement dynamics as well as the characteristic time-scales involved. This talk will report the first ever analysis of the semi-inclusive deep inelastic scattering of $\Lambda$ hyperons in the current and target fragmentation regions using the 5 GeV Jefferson Lab CLAS (EG2) datasets. It will also emphasize the ongoing efforts to correct the extracted preliminary results of multiplicity ratios and transverse momentum broadening for the apparatus acceptance and radiative effects. The results of this baryon study combined with the other EG2 mesons channels will be instrumental in understanding the space-time evolution of hadrons at intermediate beam energies. Furthermore, the results will lay a strong foundation for the hadronization studies using the upgraded CLAS12 spectrometer and the 11 GeV Jefferson Lab electron beam. [Preview Abstract] |
Tuesday, October 15, 2019 3:12PM - 3:24PM |
GH.00007: Exclusive electroproduction of pions at Hall A, Jefferson Lab Bishnu Karki Generalized Parton Distributions (GPDs) provide simultaneous spatial and momentum distribution of quarks and gluons inside the nucleons . GPDs can be accessed experimentally through hard exclusive processes like Deeply Virtual Compton Scattering (DVCS) or Deeply Virtual Meson Production (DVMP). Experiment E12-06-114 completed its data taking at the end of 2016 in Hall A at JLab. Main goal of this experiment is to measure the DVCS and exclusive $\pi^0 $ electroproduction cross-sections at various $Q^2$ for three Bjorken-x in valence regime. These result will provide stringent test of QCD factorization in hard exclusive processes over a wide range of $Q^2$ achieved with upgraded CEBAF to 12 GeV. I will show the most recent results for exclusive $\pi^0 $ electroproduction at high Bjorken-x (0.60). [Preview Abstract] |
Tuesday, October 15, 2019 3:24PM - 3:36PM |
GH.00008: Cross Section for {\$}$\backslash $gamma n$\backslash $to$\backslash $pi\textasciicircum 0n{\$} Measured at Mainz Igor Strakovsky, William Briscoe The {\$}$\backslash $gamma n$\backslash $to$\backslash $pi\textasciicircum 0n{\$} differential cross sections were evaluated for 27 energy bins and the full range of pion production angles, making use of model-dependent nuclear corrections to extract {\$}$\backslash $pi\textasciicircum 0{\$} production data on the neutron from measurements on the deuteron target. Additionally, the total photoabsorption cross section was measured. The tagged photon beam produced by the 883-MeV electron beam of the Mainz Microtron MAMI was used for the {\$}$\backslash $pi\textasciicircum 0{\$}-meson production. Our accumulation of {\$}3.6$\backslash $times 10$^{\mathrm{\wedge 6\thinspace }}\backslash $gamma n$\backslash $to$\backslash $pi\textasciicircum 0n{\$} events allowed a detailed study of the reaction dynamics. Our data are in reasonable agreement with previous A2 measurements and extend them to lower energies. The data are compared to predictions of previous SAID, MAID, and BnGa partial-wave analyses and to the latest SAID fit, MA19, that included our data. Selected photon decay amplitudes {\$}N\textasciicircum $\backslash $ast$\backslash $to$\backslash $gamma n{\$} at the resonance poles are determined for the first time. [Preview Abstract] |
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