Results of 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 unpolarized electron beams. The experiment aims to measure the $e-p$ elastic scattering cross section in an unprecedented low values of momentum transfer squared region ($\rm{Q}^2 = 2\times10^{-4} - 0.06~\rm{(GeV/c)}^2$), with a sub-percent precision. The PRad experiment utilizes a calorimetric method that is magnetic spectrometer free. Its detector 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 M$\o$ller scattering process, which was measured simultaneously within similar kinematics and detector acceptances. The windowless H$_2$-gas-flow target utilized in the experiment largely removes a typical background source, the target cell windows. In this talk, we will present results of the experiment.