Bulletin of the American Physical Society
84th Annual Meeting of the APS Southeastern Section
Volume 62, Number 13
Thursday–Saturday, November 16–18, 2017; Milledgeville, Georgia
Session G3: Proton Charge Radius Puzzle |
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Chair: Ashot Gasparian, North Carolina AT&T State University Room: MSU Building Donohoo Lounge |
Friday, November 17, 2017 1:30PM - 2:00PM |
G3.00001: Extracting the Proton Radius from Electron Scattering Data Invited Speaker: Douglas Higinbotham Many methods have been used throughout the years to extract the proton radius from electron scattering data. I will summarize both the experimental results and the various techniques used to extract the proton radius. In particular, I will show how for a given set of data the extracted proton radius depends on the technique used to make the extraction and show how machine learning regression techniques can be applied to the problem. [Preview Abstract] |
Friday, November 17, 2017 2:00PM - 2:30PM |
G3.00002: Current Results of the PRad Experiment at JLab Invited Speaker: Maxime Levillain The latest measurements of the proton radius through muonic hydrogen Lamb shift show a discrepancy of about $7\sigma$ from a global analysis of standard hydrogen Lamb shift and elastic $ep$-scattering. In order to understand this \textit{proton radius puzzle}, the PRad experiment, that was designed through an independent method, successfully performed in June 2016, taking elastic $ep$ and M{\o}ller-scattering data with rich statistics in a wide $Q^2$ range including very low momentum transfer ($Q^2 \in [10^{-4},10^{-1}]$~GeV$^2$) with very accurate angle and energy measurements to minimize the systematic uncertainties to achieve a sub-percent precision. % After briefly reminding the framework around this \textit{proton radius puzzle} and how the specific setup of the PRad experiment was designed to improve the previous measurements on elastic $ep$-scattering cross-sections, using a high efficiency and high resolution calorimeter (HyCal) and a high resolution GEM detector, the presentation will focus on the data analysis and the extraction of $ep$ scattering cross-section normalized by the well known M{\o}ller cross-section, to finally show the latest physics results from the 2.2 GeV data. [Preview Abstract] |
Friday, November 17, 2017 2:30PM - 3:00PM |
G3.00003: The MUon proton Scattering Experiment (MUSE) at the Paul Scherrer Institute Invited Speaker: Steffen Strauch While consistent results for the charge radius of the proton have been extracted from elastic electron-scattering data and through the spectroscopy of atomic hydrogen, high-precision studies of muonic hydrogen found notably smaller values for the charge radius. This so-called proton-radius puzzle raises questions ranging from experimental and methodological issues to physics beyond the standard model. The puzzle certainly calls for new measurements. The MUon proton Scattering Experiment (MUSE) at the Paul Scherrer Institute (PSI) will provide elastic scattering data off the proton with electron and muon beams of positive and negative charge in a four-momentum-transfer range from 0.002 to 0.08 GeV$^2$. Each of the four sets of data will allow the extraction of the proton charge radius; in combination, the data test possible differences of the electron and muon interactions and additionally two-photon exchange effects. The experiment is presently being commissioned at PSI. An overview of the experiment will be presented. [Preview Abstract] |
Friday, November 17, 2017 3:00PM - 3:30PM |
G3.00004: The JLab recoil polarization measurements of the proton form factors ratio GEp/GMp Invited Speaker: Charles Perdrisat A series of experiments initiated at the then new CEBAF electron accelerator in Newport News Virginia in the late nineties, resulted in unexpected results, changing significantly our understanding of the structure of the proton. These experiments used a relatively new technique to obtain the two form factors of the proton, polarization. An intense beam of highly polarized electrons with energy up to 6 GeV was made to interact with protons in a hydrogen target, and the resulting polarization of the recoiling protons was obtain from a second interaction in a polarimeter. After a short introduction I will introduce the subject of elastic electron scattering, describe some of the apparatus required for such experiments, show results and then give a brief outline of several theoretical considerations to put the results in a proper perspective. [Preview Abstract] |
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