The Proton Charge Radius Experiment (PRad) at JLab

In order to investigate the proton charge radius puzzle,
the PRad experiment (E12-11-106) was performed in 2016 in Hall B at Jefferson Lab, with both 1.1 and 2.2 GeV electron beams. It aims to measure the e-p elastic scattering cross section in an unprecedented low values of momentum transfer squared region (Q² = 2×10^-4∼0.06 (GeV/c)²) with a sub-percent precision. The PRad experiment utilizes a calorimetric method that is magnetic spectrometer free. Its setup includes a large acceptance and high resolution calorimeter (HyCal), and two large area, high spatial resolution Gas Electron Multiplier (GEM) detectors. To have a better control over the systematic uncertainties, the absolute e-p elastic scattering cross section is normalized to that of the well-known Møller scattering process, which was measured simultaneously within similar kinematics and acceptances. The windowless H₂-gas-flow target utilized in the experiment largely removes a typical background source, the target cell windows. In this talk, we will discuss details of the data analysis and present the proton charge radius result.