Bulletin of the American Physical Society
APS April Meeting 2022
Volume 67, Number 6
Saturday–Tuesday, April 9–12, 2022; New York
Session L11: Mini-symposium: Multidimensional Structure of Hadrons IVMini-Symposium Recordings Available
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Sponsoring Units: DNP GHP Chair: Aurore Courtoy Room: Majestic |
Sunday, April 10, 2022 3:45PM - 3:57PM |
L11.00001: Transverse charge density and the radius of the proton Alexander Gramolin, Rebecca Russell A puzzling discrepancy exists between the values of the proton charge radius obtained using different experimental techniques: elastic electron-proton scattering and spectroscopy of electronic and muonic hydrogen. The proton radius is defined through the slope of the electric form factor, GE(Q2), at zero four-momentum transfer, which is inaccessible in scattering experiments. We propose a novel method for extracting the proton radius from scattering data over a broad Q2 range rather than attempting to directly determine the slope of GE at Q2=0. This method relates the radius of the proton to its transverse charge density, which is the two-dimensional Fourier transform of the Dirac form factor, F1(Q2). We apply our method to reanalyze the extensive data obtained by the A1 Collaboration [J.C. Bernauer et al., Phys. Rev. Lett. 105, 242001 (2010)] and extract a radius value, 0.889(5)stat(5)syst(4)model fm, that is consistent with the original result. We also provide new parametrizations for the Dirac and Pauli form factors and the transverse charge and magnetization densities of the proton. Our reanalysis shows that the proton radius discrepancy cannot be explained by issues with fitting and extrapolating the A1 data to Q2=0. |
Sunday, April 10, 2022 3:57PM - 4:09PM |
L11.00002: Deep Virtual Neutral Pion Production at 6.6 and 8.8 GeV with CLAS12 Francois-Xavier Girod Generalized Parton Distributions (GPDs) parameterize the amplitude for Deep Exclusive Hadronic Processes, |
Sunday, April 10, 2022 4:09PM - 4:21PM |
L11.00003: Deeply Virtual Neutral Pion Electro-production Cross Section Off Proton at CLAS12 Robert E Johnston Deeply virtual exclusive reactions provide unique channels to study both transverse and longitudinal properties of the nucleon simultaneously, allowing for a 3D image of nucleon substructure. This presentation will discuss work towards extracting an absolute cross section for one such exclusive process, deeply virtual neutral pion production, using 10.6 GeV electron scattering data off a proton target from the CLAS12 experiment in Jefferson Lab Hall B. This measurement is important as exclusive meson production has unique access to the chiral odd GPDs, and is also a background for other exclusive processes such as DVCS, making the determination of this cross section crucial for other exclusive analyses. |
Sunday, April 10, 2022 4:21PM - 4:33PM |
L11.00004: First measurement of timelike Compton scattering with CLAS12 at JLAB Stepan Stepanyan
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Sunday, April 10, 2022 4:33PM - 4:45PM |
L11.00005: Transversely polarized Timelike Compton Scattering off the proton in Hall C at Jefferson Lab Brannon A Semp, Marie Boer Generalized Parton Distributions, functions correlating the transverse distribution of partons with their longitudinal momenta, can be interpreted in terms of "3D images" of the nucleon. They can be accessed in hard exclusive processes, such as Timelike Compton Scattering (TCS). This process is measured in the reaction γ(P)->γ*(p)->e+e-(P) (photoproduction of a lepton pair at high invariant mass), where the virtual photon is scattered off a quark, and interferes with another process called Bethe-Heitler (BH). The spacelike-equivalent of TCS, (spacelike) Deeply Virtual Compton Scattering has been widely studied over the past two decades and provided data to parametrize GPD models. However, we still lack experimental data on some GPDs such as the GPD E, which contains information about the nucleon polarization and is needed to study parton's angular momenta from GPDs. We analyzed data in the context of the development of an experiment at JLab Hall C aimed at extracting the GPDs H and E from TCS. We will discuss our goals, our analysis method, and present projections of TCS transversely polarized spin asymmetries for both a circularly polarized and unpolarized beam and their sensitivities to the parametrization of the GPD E. |
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