Speaker
Description
The proton charge radius ($r_p$) is a fundamental quantity for understanding QCD and is essential for high-precision QED calculations. It is typically measured using hydrogen spectroscopy or elastic electron-proton (e-p) scattering. Since 2010, there has been the so-called “proton charge radius puzzle,” which arose from the results of muonic hydrogen spectroscopy. To further address the puzzle, the PRad-II experiment in Hall B at Jefferson Lab conducted an upgraded, magnetic-spectrometer-free measurement of elastic e-p scattering to extract the $r_p$. Building upon the success of the PRad experiment, which supported a smaller value of $r_p$, PRad-II aims to improve the precision by a factor of 3.5, with a total uncertainty of ~0.0043 fm. To achieve this unprecedented precision, PRad-II implemented several upgrades: a new scintillator veto detector to reach extremely low $Q^2$ values, down to the level of $10^{-5}$ $GeV^2$ at extreme forward angles, a second GEM tracking plane to improve background subtraction and vertex reconstruction, and a new fADC readout system for the high-resolution electromagnetic calorimeter. PRad-II is currently taking data in Hall B at JLab, will complete data-taking in June. In this poster, I will present the status of data-taking and some preliminary analysis results on behalf of the PRad-II Collaboration.