Bulletin of the American Physical Society
APS April Meeting 2019
Volume 64, Number 3
Saturday–Tuesday, April 13–16, 2019; Denver, Colorado
Session R09: Proton Charge Radius and Low-Energy Properties. |
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Sponsoring Units: GHP DNP Chair: Tim Hobbs, Southern Methodist University Room: Sheraton Governor's Square 11 |
Monday, April 15, 2019 1:30PM - 1:42PM |
R09.00001: The Proton Charge Radius Experiment (PRad) at JLab Weizhi Xiong In order to investigate the proton charge radius puzzle, |
Monday, April 15, 2019 1:42PM - 1:54PM |
R09.00002: The Form Factor Program with the Super BigBite Spectrometer (SBS) Peter A Monaghan The Super Bigbite Spectrometer (SBS) has been developed for precise measurements of the proton electric form factor (GEP) and the neutron electric and magnetic form factors (GEn and GMn), at a momentum transfer higher than ever previously explored. These form factor measurements will be made in a suite of experiments to be run in Hall A at the Thomas Jefferson National Accelerator Facility (JLab). The SBS apparatus consists of a new, large acceptance dipole magnet, and new detector packages which are currently under construction. The present GEP form factor measurements are limited at a momentum transfer of Q2 = 3.4 (GeV/c)2. The new experiments will extend the Q2 range up to 10 (GeV/c)2, while significantly improving the precision of the measurements. An overview of the SBS apparatus and the physics measurements of the GEP , GMn and GEn will be presented. |
Monday, April 15, 2019 1:54PM - 2:06PM |
R09.00003: A Future Two-photon Exchange Experiment at DESY Douglas Hasell The discrepancy between unpolarised and polarised measurements of the proton form factor ratio μp GpE / GpM is still not resolved. Recent experiments: VEPP-3, CLAS, and OLYMPUS; measured the two-photon exchange contribution but only at Q2 < 2.3 (GeV/c)2 where the discrepancy is not so evident and two-photon exchange contributions are small, ∼1%. Two-photon exchange is still considered the leading explanation for the discrepancy but experiments are needed that probe higher Q2 where larger two-photon exchange contributions can be expected. A possibility exists in the near future at DESY that would reach Q2 ∼ 4.6 (GeV/c)2. Higher Q2 measurements could also be possible. The proposed experiment and Monte Carlo simulations to investigate the event rates and background conditions are presented. |
Monday, April 15, 2019 2:06PM - 2:18PM |
R09.00004: Beam Particle Tracking for MUSE Tanvi Patel, Michael Kohl The Muon Scattering Experiment (MUSE) at Paul Scherrer Institute (PSI) is being prepared to resolve the proton radius puzzle – the six-standard deviation discrepancy between proton charge radius measurements with electronic and muonic probes, respectively. MUSE is designed to measure the proton charge radius with elastic electrons and muons scattering simultaneously and with both charge polarities. For an accurate determination of the lepton scattering angle, event-by-event beam particle tracking is required to reconstruct the incoming particle track. A telescope of Gas Electron Multipliers (GEM), exposed to a high flux of beam particles is used to reconstruct the incoming tracks with high spatial resolution while representing minimal material for the beam to pass through. The status of the GEM performance will be reported in the presentation. |
Monday, April 15, 2019 2:18PM - 2:30PM |
R09.00005: Proton charge radius extraction from electron scattering data using dispersively improved chiral effective field theory Jose Manuel Alarcón, Douglas W Higinbotham, Christian Weiss, Zhihong Ye We will present an extraction of the proton charge radius from the elastic form factor data using a theoretical frame- work combining chiral effective field theory and dispersion analysis. Complex analyticity in the momentum transfer correlates the behavior of the spacelike form factor in different Q2 regions and permits the use of data up to Q2 ~ 0.5 GeV2 to constrain the radius. The radius appears as a parameter in the theoretical predictions of the form factors at finite Q2 and can be determined by comparing the predictions for different radii with the finite-Q2 data, without extrapolation to Q2 = 0. With this technique, we obtain a radius of 0.844(7) fm, consistent with the high-precision muonic hydrogen results. |
Monday, April 15, 2019 2:30PM - 2:42PM |
R09.00006: Proton Internal Dynamics from Thermodynamics Arne Peter Olson
Proton Internal Dynamics from Thermodynamics The goals of this work are to explain the origin of the proton’s mass, and to explain why it is stable. Predictions based on the Standard Model are unable to accurately predict measured physical quantities of charge radius, mass radius, magnetic moment, and magnetic-moment-weighted charge radius. New physics, derived with guidance from thermodynamics and statistical mechanics, enables constructing an extremely accurate model for the mass and charge structure of the proton. What makes this model unique is that it predicts measured proton properties to very high precision, using derived component properties of mass, charge, time-averaged radii, energies, and angular momenta. The proton is shown to be a dynamic system which satisfies laws of thermodynamics derived from Einstein-Bose statistics. Application of those statistics yield uncharged and charged component masses. Applying laws of mass conservation and momentum conservation enables deducing the energy, spatial distribution and motion of all components. A complete dynamic model of the proton is derived. For example, the magnetic moment is predicted as 2.792705 μN, which is within 0.005% of measurement. The proton’s mass is 935.045 MeV (photonic) and 3.2277 MeV (charge).
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Monday, April 15, 2019 2:42PM - 2:54PM |
R09.00007: Non-spherical bags. Gerard J Stephenson, T. Goldman There are no solutions of the Dirac equation confined to a rectilinear bag with simple MIT bag boundary conditions [1]. A study with spheroidal deformation [2] also produced this result. However, that study also demonstrated that the addition of a chiral phase on the boundary allowed for sensible solutions. We shall present the results of extending this notion to the rectilinear case. [1] A. Chodos, R. L. Jaffe, K. Johnson, C. B. Thorn, and V. F. Weisskopf, Phys. Rev. D9, (1974) 3417. |
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