Bulletin of the American Physical Society
APS April Meeting 2022
Volume 67, Number 6
Saturday–Tuesday, April 9–12, 2022; New York
Session X10: Electromagnetic InteractionsRecordings Available
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Sponsoring Units: DNP Chair: Evangeline Downie, George Washington University Room: Lyceum |
Tuesday, April 12, 2022 10:45AM - 10:57AM |
X10.00001: New data on the proton form factor at low-Q^2 from Mainz using a cluster/gas-jet target Jan C Bernauer Motivated by the decade old, still not fully resolved proton radius puzzle and the striking difference in low-Q^2 form factor extractions between the PRad and Mainz measurements, the A1 collaboration measured several kinematic points in the overlap region between the two data sets. To improve on previous measurements, a cluster/gas-jet target and additional halo shielding and veto detectors were installed. In the talk, we discuss these upgrades and the results of the first measurements. |
Tuesday, April 12, 2022 10:57AM - 11:09AM |
X10.00002: Particle Identification Trigger for MUSE* Shraddha Dogra The Muon proton Scattering Experiment (MUSE) uses a mixed beam of electrons, muons and pions from the PiM1 beam line of the Paul Scherrer Institute (PSI) in Villigen, Switzerland. The experiment will simultaneously measure elastic scattering cross-sections of both electrons and muons, from a liquid hydrogen target, and will extract the charge radius of the proton. Comparison of scattering cross sections will provide data for the proton radius puzzle, and comparison of cross sections obtained with positive and negative polarity beams will determine two-photon exchange radiative corrections. Correct particle identification at the trigger level is required to obtain a data set that is mainly from electron and muon scattering, rather than a data set that is dominated by pion scattering. This is done using a particle identification trigger (PID). I will discuss recent developments and results related to the PID trigger along with other aspects of experiment triggering. |
Tuesday, April 12, 2022 11:09AM - 11:21AM |
X10.00003: Overview of MUSE Experiment Wan Lin The MUon proton Scattering Experiment (MUSE) at the PiM1 beam line of the Paul Scherrer Institute is simultaneously measuring the elastic scattering of electrons and muons from a liquid hydrogen target to extract the charge radius of the proton. Both beam polarities will be 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. This talk will give a brief overview of the MUSE experiment, including the initial motivation, measurement capability and detector setup. There will also be a brief discussion on the current status of the collaboration and the progress of current beam-time. |
Tuesday, April 12, 2022 11:21AM - 11:33AM |
X10.00004: Beam Stability in PSI MUSE Rujuta Mokal The Muon proton Scattering Experiment (MUSE) uses a mixed beam of electrons, muons and pions from the PiM1 beam line of the Paul Scherrer Institute (PSI) in Switzerland. The aim of the experiment is to measure elastic scattering cross-sections for both electrons and muons, from a liquid hydrogen target. From this, the charge radius of the proton will be extracted, providing data for the proton radius puzzle - a 4%discrepancy in the proton radius when measured through muonic hydrogen spectroscopy as compared to regular hydrogen spectroscopy and electron-proton scattering. Measuring precise cross sections to compare e and mu and the two beam polarities requires stability of the beam and electronics. I will be discussing recent analyses and observations of the time particles arrive at the experiment detectors relative to the accelerator clock. The studies were done to establish the stability of MUSE detectors and electronics and the PiM1 channel at PSI. Changes in the beam momentum of order 0.1% lead to measurable, correlated changes in the times of muons and pions relative to electrons, of a few tens of ps. |
Tuesday, April 12, 2022 11:33AM - 11:45AM |
X10.00005: PRad II: An Upgraded Electron-Proton Scattering Experiment for High Precision Measurement of the Charge Radius of the Proton at Jefferson Lab Vladimir Khachatryan
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Tuesday, April 12, 2022 11:45AM - 11:57AM |
X10.00006: Direct Measurement of Radiative Effects for ep Elastic Scattering at Very Low Q2 Chao Peng The recent PRad experiment at Jefferson Lab has precisely measured the cross sections for elastic electron proton scattering at four momentum transfer square (Q2) from 2×10-4 to 6×10-2 GeV2/c2. The charge radius of proton was extracted based on the measured proton form factors at very low Q2. This experiment utilized a high precision, hybrid calorimeter (HyCal) which can precisely determine the energy and position of electrons and photons. The inner part of HyCal, consisted of a 34×34 array of PbWO4 modules, can separate two incident particles with a distance greater than about 29 mm (√2 of the module size) on the detection plane. Together with the GEM detectors located in front of the HyCal, which serve as a veto detector for neutral particles, the PRad detector system is capable of measuring and identifying the scattered electrons and the radiative photons simultaneously from the elastic ep scattering process. In this talk, I will present the preliminary results of the direct radiative effects measurement from the PRad experiment. I will also discuss the expected improvements of the results with the upcoming PRad-II experiment. |
Tuesday, April 12, 2022 11:57AM - 12:09PM |
X10.00007: TPEX@DESY - A Two-Photon Exchange Experiment at DESY Ievgen Lavrukhin The striking discrepancy in the proton form factor ratio, μpGpE/GpM, measured using unpolarized and polarized techniques is still not resolved. The proposed explanation is that hard two-photon exchange (TPE) is responsible. Hard TPE is difficult to calculate without significant model dependence, and has generally not been included in radiative corrections. Furthermore, three recent experiments (VEPP-3, CLAS and OLYMPUS) found only a small contribution but were limited to relatively low Q2 < 2.5 (GeV/c)2 where the discrepancy is not pronounced. A new test beam experiment, TPEX@DESY, would use a proposed 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 Q2 range up to 4.7 (GeV/c)2, where the discrepancy in the proton form factor ratio is significant and where the expected hard TPE contribution is predicted to be large. An overview of the proposed experiment as well as results from the recent tests of a 5x5 prototype lead tungstate calorimeter at the DESY test beam facility will be presented and discussed. |
Tuesday, April 12, 2022 12:09PM - 12:21PM |
X10.00008: Measurements of Two-Photon Exchange Contributions to the Electron-Neutron Elastic Scattering Cross-Section Using the SBS Experimental Setup at Jefferson Lab John A Boyd The first two experiments to measure nucleon electromagnetic form factors to high four-momentum transfer $Q^2$ have recently concluded (Feb. 2022) at Jefferson Lab (JLab) using the Super BigBite Spectrometer (SBS). SBS is a large-acceptance spectrometer designed to handle high fluxes and high-momentum particles produced by JLab's 11\,GeV/c electron beam. One of them is nTPE: a measurement of the two-photon exchange contribution to the electron-neutron elastic scattering cross section at a four-momentum transfer of $Q^2 = 4.5$\,(GeV/c)$^2$. This experiment will assess the two photon contribution by Rosenbluth separation -- with precision at least 20-50 times greater than previously achieved -- and with accurate values of \nicefrac{$G^{n}_{E}$}{$G^{n}_{M}$} for the neutron found in companion SBS experiments. The experimental goal is achieved by measuring the ratio of rates \nicefrac{$e$-$n$}{$e$-$p$} for determination of the ratio of cross sections, and the precisely known Rosenbluth ratio for the proton. The trackers in BigBite and SBS are gaseous electron multipliers (GEMs). GEMs of various types and configurations are used to break analytical ambiguity created by high rates and improve tracking efficiencies. These GEMs are critical tracking components for all present and future high-impact experiments of the SBS program. |
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