Bulletin of the American Physical Society
2013 Fall Meeting of the APS Division of Nuclear Physics
Volume 58, Number 13
Wednesday–Saturday, October 23–26, 2013; Newport News, Virginia
Session FD: Proton Charge Radius |
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Chair: Ashot Gasparian, North Carolina A&T Room: Grand Ballroom IV |
Thursday, October 24, 2013 4:00PM - 4:12PM |
FD.00001: The PRad Experiment at JLab Dipangkar Dutta Recent measurements of the proton charge radius in muonic hydrogen, have found a large ($>$ 7 $\sigma$) discrepancy compared to the charge radius extracted from regular hydrogen, using either atomic spectroscopy or electron scattering. We are preparing a new high precision measurement of the proton charge radius using electron scattering (PRad) at JLab. This experiment will be the first magnetic spectrometer free measurement of the proton charge radius, using a novel window-less gas flow target and a high resolution calorimeter (HyCal). The systematic uncertainties will be controlled by detecting the elastic and the M\"{o}ller scattered electrons simultaneously within the same geometric acceptance. The experiment will cover a $Q^2$ range of $10^{-4} - 10^{-2}$ GeV$^2$, reaching the lowest $Q^2$ of any previous electron-proton scattering experiment. We will discuss the status of this experiment as it is being prepared to run in Hall-B, as soon as beam is available at the upgraded JLab. [Preview Abstract] |
Thursday, October 24, 2013 4:12PM - 4:24PM |
FD.00002: Target Simulation for PRad Experiment Yang Zhang The recently approved PRad experiment at Jefferson Laboratory Hall B aims to extract the proton charge radius at the sub-percent level using unpolarized electron-proton elastic scattering cross section in very low Q$^2$ region. This experiment will provide an important opportunity to address the ``proton radius puzzle.'' A novel feature of this experiment is the utilization of a windowless gas flow target, which greatly reduces the background contribution from the target cell. A differential pumping system has been designed in order to obtain high target density while at the same time maintain low vacuum pressure along the beamline. This talk will present the results of a calculation of the target density with the designed target and pumping system using finite element analysis software package COMSOL. This work is supported by the U.S. Department of Energy under contract number DE-FG02-03ER41231 and the National Science Foundation under award number PHY-1229153. [Preview Abstract] |
Thursday, October 24, 2013 4:24PM - 4:36PM |
FD.00003: Radiative corrections beyond the ultra relativistic approximation for the PRad experiment Mehdi Meziane The clear 7$\sigma$ discrepancy between measurements of the proton charge radius from muonic hydrogen Lamb shift and those from hydrogen Lamb shift and electron scattering lead to both intense theoretical and experimental efforts to understand and explain this difference. In this regard, an experiment (PRad) based on unpolarized ep elastic scattering cross section
measurements, has been proposed and approved at Jefferson Laboratory to extract the proton charge radius up to momentum transfer squared $Q^{2}$ as low as 2$\times$10$^{-4}$ (GeV/c)$^{2}$. Reaching such a small $Q^{2}$ region requires
reliable knowledge of radiative corrections. Results of a complete calculation of radiative corrections for unpolarized elastic ep and M\"oller scatterings performed within a covariant formalism beyond the ultra relativistic approximation $m_{e}^{2}< |
Thursday, October 24, 2013 4:36PM - 4:48PM |
FD.00004: The MUSE Measurement of the Proton Radius at PSI $\pi$M1: Overview Evangeline J. Downie The Proton Radius Puzzle, the difference between the proton radius measured using muonic hydrogen and the same quantity measured using atomic hydrogen and electron-proton elastic scattering, remains unresolved after three years. The MUon proton Scattering Experiment (MUSE) at the Paul Scherrer Institut (PSI) $\pi$M1 beam line is intended to help resolve the Puzzle through measurements of $\mu^{\pm}p$ and $e^{\pm}p$ elastic scattering. Measuring scattering of electrons and muons at the same time should provide a direct $e$/$\mu$ comparison with reduced systematic uncertainties. Measuring with both positive and negative beam charges allows two-photon exchange contributions to be studied. This talk will provide an overview of the MUSE motivation, measurements, schedule and expected results. [Preview Abstract] |
Thursday, October 24, 2013 4:48PM - 5:00PM |
FD.00005: Simulation study for PRad experiment Chao Peng Proton size puzzle was recently raised by the measurement of muonic hydrogen Lamb shift at Paul Scherrer Institute (PSI). The PSI value greatly increased the precision of the rms charge radius of the proton, but it deviated from the Committee on Data for Science and Technology (CODATA) 2010 recommended value by 7 $\sigma$. To investigate this discrepancy, the PRad experiment at Jefferson Lab was proposed to extract the proton charge radius with a sub-percent uncertainty by measuring the cross-sections of unpolarized electron-proton elastic scattering in a very low Q$^2$ region. Such a high precision measurement requires a thorough and accurate knowledge of the possible background sources. A simulation code based on Geant 4 was developed to characterize and quantify the background. Results of the simulation and several methods to suppress the background will be presented. This work is supported by the U.S. Department of Energy under contacts number DE-FG02-03ER41231 and U.S. National Science Foundation under contact number PHY-1229153. [Preview Abstract] |
Thursday, October 24, 2013 5:00PM - 5:12PM |
FD.00006: The MUSE Measurement of the Proton Radius at PSI $\pi$M1: Simulations Katherine Myers The MUon proton Scattering Experiment (MUSE) at the Paul Scherrer Institut (PSI) $\pi$M1 beam line uses secondary particles generated from the interactions of a proton beam in a carbon production target. As a result, the beam has low intensity and large emittance compared to electron beams typically used for electromagnetic studies. To partially compensate, MUSE uses a large solid angle nonmagnetic spectrometer to measure $\mu^{\pm}p$ and $e^{\pm}p$ elastic scattering. The combination of these features makes the experimental challenges quite different from the standard measurement of nucleon form factors with electron beams and magnetic spectrometers, necessitating extensive simulations to ensure that potential issues are identified and under control. I will discuss the MUSE simulations and the challenges facing the experiment. [Preview Abstract] |
Thursday, October 24, 2013 5:12PM - 5:24PM |
FD.00007: The MUSE Measurement of the Proton Radius at PSI $\pi$M1: Scattering Test Ronald Gilman The MUon proton Scattering Experiment (MUSE) measurements at the Paul Scherrer Institut (PSI) $\pi$M1 beam line utilizes a mixed $e/\mu/\pi$ beam to measure $\mu^{\pm}p$ and $e^{\pm}p$ elastic scattering. The experiment plans to use a large-acceptance non-magnetic spectrometer of wire chambers and scintillators to measure scattered particles. Triggering will also require determining beam particle type in hardware. Prominent backgrounds include in-flight decays of $\pi$'s and $\mu$'s in the beam, along with scattering from beam line detectors. To test elements of the plan, we performed a small scattering experiment during the 2013 test run with a plastic target, and a spectrometer consisting of GEM chambers and a fast scintillator for triggering. The scattering measurement will be described and some results will be presented. [Preview Abstract] |
Thursday, October 24, 2013 5:24PM - 5:36PM |
FD.00008: The MUSE Measurement of the Proton Radius at PSI $\pi$M1: Radiative Corrections and Two-Photon Exchange Andrei Afanasev The MUon proton Scattering Experiment (MUSE) at the Paul Scherrer Institut (PSI) $\pi$M1 beam line is intended to measure the proton charge radius from $\mu^\pm p$ and $e^\pm p$ elastic scattering. In this talk we present calculations and discuss the role of electromagnetic radiative corrections for the MUSE experiment. Since the muon is heavier than an electron, the bremsstrahlung corrections are reduced in the muon case. However, the two-photon corrections and the interference between lepton and proton bremsstrahlung are less dependent on the lepton mass. Model estimates of the two-photon corrections are presented. The MUSE experiment will provide a capability to measure two-photon effects by analyzing lepton charge dependence of the scattering cross sections. [Preview Abstract] |
Thursday, October 24, 2013 5:36PM - 5:48PM |
FD.00009: The MUSE Measurement of the Proton Radius at PSI $\pi$M1: Beam Studies Vincent Sulkosky The MUon proton Scattering Experiment (MUSE) measurements at the Paul Scherrer Institut (PSI) $\pi$M1 beam line utilizes a mixed $e/\mu/\pi$ beam to measure $\mu^{\pm}p$ and $e^{\pm}p$ elastic scattering. The beam properties have not previously been characterized at the level needed for MUSE. In 2012 and 2013, we used systems of fast scintillators, scintillating fiber detectors, beam Cerenkovs, and GEM chambers to characterize the beam properties (particle fluxes, emittances, and RF time separation of particles) and to test whether the beam is indeed adequate for the planned MUSE measurements. In this talk, I will describe the test beam measurements and the obtained results. [Preview Abstract] |
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