Bulletin of the American Physical Society
2021 Fall Meeting of the APS Division of Nuclear Physics
Volume 66, Number 8
Monday–Thursday, October 11–14, 2021; Virtual; Eastern Daylight Time
Session JK: Nucleon Charges and Form Factors |
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Chair: Amy Nicholson, UNC Room: Arlington |
Wednesday, October 13, 2021 9:30AM - 9:42AM |
JK.00001: Overview of the Muon Proton Scattering Experiment, MUSE Haley R Reid The proton radius puzzle became prominent in 2010 when the muonic spectroscopy result from the CREMA collaboration found that the charge radius was at least five standard deviations smaller than the previously accepted value. In the past eleven years, a myriad of experiments have utilized different methods to gather information and learn more about the structure of the proton and its charge radius. The MUon-proton Scattering Experiment - MUSE - at Paul Scherrer Institut (PSI) in Villigen, Switzerland, aims to reassess the proton charge radius and the discrepancies that remain by performing the first simultaneous measurement of elastic electron and muon scattering off the proton with the PiM1 beamline at PSI. In addition, MUSE will be able to directly measure two-photon exchange effects by measuring both charge states. This talk will give an overview of MUSE, including the physics motivations, experimental hardware configuration and capabilities, as well as the current status of the collaboration. |
Wednesday, October 13, 2021 9:42AM - 9:54AM |
JK.00002: Lead-glass Calorimeter at MUSE Wan Lin, Lin Li, Steffen Strauch, Ronald Gilman The MUon proton Scattering Experiment (MUSE) at the PiM1 beam line of the Paul Scherrer Institute works to simultaneously measure elastic scattering of electrons and muons from a liquid hydrogen target to extract the charge radius of the proton. Both beam polarities are measured over the course of the experiment. By comparing the four scattering cross sections, the experiment will provide unique muon proton scattering data with a precision sufficient to address the proton radius puzzle, and will directly measure two-photon exchange effects for both muons and electrons. The lead glass calorimeter at MUSE was developed primarily to measure initial-state radiation for use in radiative corrections. It can also be used to study the energy of beam particles and the stability of the energies, complementing measurements based on the dipole magnet settings and beam particle RF times. While the other techniques determine the beam momentum out of the channel, the calorimeter determines the beam energy after it has passed through beamline detectors and the cryotarget. Thus, it directly provides a measurement of the energy loss in these materials, verifying simulations and allowing the vertex kinematics to be reliably determined. This presentation will discuss these additional energy measurements done by the calorimeter. |
Wednesday, October 13, 2021 9:54AM - 10:06AM |
JK.00003: Study of Radiative-Correction Uncertainties in MUSE with ESEPP Lin Li, Steffen Strauch, Anne Flannery, Wan Lin The MUon Scattering Experiment (MUSE) at Paul Scherrer Institute (PSI) intends to measure the proton charge radius from elastic electron-proton and muon-proton scattering data with positively and negatively charged beams in a four-momentum-transfer range from 0.002 to 0.08 GeV2. The data will test possible differences between the electron and muon interactions and two-photon exchange effects. Radiative corrections, which depend on detector properties, are essential to reduce uncertainties in the proton radius extraction. In this talk, the effects of using a downstream photon calorimeter on the radiative corrections are studied. Based on the ESEPP (Elastic Scattering of Electrons and Positrons on Protons) event generator, the size of radiative corrections for electron and muon scattering and their uncertainties were determined and will be discussed. |
Wednesday, October 13, 2021 10:06AM - 10:18AM |
JK.00004: Evaluation of GEM tracking quality at MUSE Angel Christopher, Tanvi Patel, Jesmin Nazeer, Michael Kohl The MUon Scattering Experiment (MUSE) at Paul-Scherrer Institute (PSI) will measure the proton charge radius by scattering of muons and electrons from the proton. The experiment uses a telescope of three Gas Electron Multiplier (GEM) detectors to track the beam paticle that is later scattered. This presensation will show the transformation of the track location at each GEM element compared with the local coordinates of the hits on each element. Three GEM elements will be used to make a track and the quality of the track will be assessed using the hits on the fourth GEM element. |
Wednesday, October 13, 2021 10:18AM - 10:30AM |
JK.00005: Abstract Withdrawn
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Wednesday, October 13, 2021 10:30AM - 10:42AM |
JK.00006: Abstract Withdrawn
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Wednesday, October 13, 2021 10:42AM - 10:54AM |
JK.00007: Probing Nucleon Polarizabilities with the Crystal Ball and TAPS in the A2 Tagged Photon Facility at MAMI Evangeline J Downie The polarizabilies of the nucleon are fundamental properties which characterize the nucleon's internal structure and dynamics. They play a role in many areas of physics. Uncertainties in polarizabilities play a role in the Proton Radius Problem, the electromagnetic contribution to the proton-neutron mass difference; and even in astrophysics, where they define the neutron star properties. Experimental capability over recent years has reached, and is further developing in some areas, to the point where higher precision extractions of the scalar polarizabilities can be made, and extractions of the spin polarizabilities with reasonable statistical precision have become attainable. Using the Crystal Ball and TAPS detectors in the A2 Tagged Photon facility of the MAinzer MIcroton (MAMI) accelerator, we aim to exploit, and further develop, this technology to further understand the structure and dynamics of the nucleon, and provide a clean test of Chiral Effective Field theories, by accessing the polarizabilities in Compton scattering experiments. We will report on the staus and recent results of the Compton Scattering program, and summarize future experiments. |
Wednesday, October 13, 2021 10:54AM - 11:06AM |
JK.00008: TPEX@DESY - Measuring Two-Photon Exchange at the DESY Test Beam Facility Ethan Cline The striking discrepancy in the proton form factor ratio, $\mu_p G_E^p/G_M^p$, measured using unpolarized and polarized techniques is still not resolved. The leading explanation is hard two-photon exchange (TPE). Hard TPE is difficult to calculate without significant model dependence, and has generally not been included in radiative corrections. Three recent experiments found only a small contribution but were limited to relatively low $Q^2$ where the discrepancy is not clear. A new proposal, TPEX@DESY, would use an extracted beam at the DESY test beam facility together with a liquid hydrogen target and high precision lead tungstate calorimeters to measure hard TPE at higher beam energies. This would permit measurements in a $Q^2$ regime where the discrepancy in the proton form factor ratio is significant and where the expected hard TPE contribution is predicted to be large. The motivation and overview of the proposed measurements will be presented. |
Wednesday, October 13, 2021 11:06AM - 11:18AM |
JK.00009: Renormalization of the fermion-charge due to electromagnetic self-interactions in time-dependent, relativistic quantum mechanics Athanasios Petridis, Timothy Kutnink, David Atri-Schuller, Scott Barcus The time-dependent electromagnetically self-coupled Dirac equation is solved numerically by means of the MSD2 algorithm with special attention to stability. The expectation values of several dynamic operators are evaluated as functions of time and the asymptotic, i.e., physical values are obtained. These include the fermion dynamic mass, and charge. The dependence of the expectation values on the spatial-grid size is evaluated and yields finite results due to the finiteness and continuity of the spinor. A statistical method, employing a canonical ensemble whose temperature is the inverse of the spatial-grid size, is used to remove the momentum-dependence. A result for each spatial-grid size value is obtained and the continuum limit is taken to calculate the fermion renormalized mass and charge. The charge renormalization is attributed to the contribution of the negative-energy components of the time-dependent Dirac spinors. The renormalization mass correction is 10% and the charge correction is about 5%. |
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