Speaker
Description
In 2010, a new method using muonic hydrogen spectroscopy led to a proton charge radius ($r_p$) result that was nearly ten times more precise but significantly smaller than results obtained using the two traditional methods, namely e-p scattering and ordinary Hydrogen spectroscopy. This
discrepancy triggered the so-called "proton charge radius puzzle". To investigate this discrepancy, the PRad collaboration performed a new experiment in 2016 in Hall B at the Thomas Jefferson National Accelerator Facility. With both 1.1 and 2.2 GeV electron beams, the experiment measured the e-p elastic scattering cross sections in an unprecedentedly low values of momentum transfer squared region ($Q^2 = 2.1 \times 10^{-4} - 0:06$ (GeV/c)$^2$),
with a sub-percent precision. The PRad experiment utilized a magnetic-spectrometer-free setup, which was based on a large acceptance and high resolution calorimeter (HyCal), a plane of two large-area Gas Electron Multiplier (GEM) detectors, and a windowless H2 gas-flow target. In this talk, I
will discuss details of the data analysis and present the results of this experiment. I will also discuss briefy the PRad-II experiment, which will improve the uncertainty of $r_p$ by a factor of approx 4 compared to that of PRad.
