Elastic e+p to u+p Scattering Cross Section Ratios at 210 MeV/c with the MUon Scattering Experiment

Abstract

The proton radius puzzle names the discrepancy between measurements of the proton charge radius done with atomic hydrogen spectroscopy, muonic hydrogen spectroscopy, and elastic electron-proton scattering. This puzzle initialized in 2010 with the first published results of proton radius extraction from muonic hydrogen spectroscopy, and since then, the discrepancy found has been investigated without a conclusive result. The MUon proton Scattering Experiment (MUSE) simultaneously measures elastic electron-proton and muon-proton scattering using the PiM1 beam line at Paul Scherrer Institute in Villigen, Switzerland. Using both positive and negative beam polarities, MUSE will extract the proton charge radius by scattering o↵ a liquid hydrogen target and contribute precise data to the investigation of the proton radius puzzle. MUSE also aims to test lep- ton universality by comparing the scattering cross sections for electrons and muons at both polarities. In the quest for the radius, additional interesting physics such as two-photon- exchange e↵ects and the extraction of the electric and magnetic form factors are included in the physics goals of MUSE. The detector components of MUSE and their respective roles in data collection and anal- ysis are explained, as well as the trigger and data acquisition employed by MUSE. This thesis highlights and details the design, construction, commissioning, and operation of the liquid hydrogen target and all of its system components, which have operated successfully in beam times since 2019. Improvements to the system and their motivations will also be discussed. This thesis will discuss analysis development projects including path length reconstruction of scattered particles to contribute to scattering event identification, trigger reconstruction within the analysis for selecting on events that fire desired triggers, and corrections to the incident beam flux at the target to improve the accuracy of the scattering cross section calculation. Scattering data from ±210 MeV/c is analyzed and di↵erential cross section results are extracted. These di↵erential cross section and cross section ratio results will be presented for ep and μp elastic scattering and discussed with respect to MUSE’s physics goals as well as the test for lepton universality.