PRad-II: Improving the High Precision e-p Proton Charge Radius Measurement and Preparing the Experimental Apparatus*

The Hybrid Calorimeter (HyCal) is a well-tested and high-precision calorimeter that has been used in a variety of experiments since its commissioning. The PRad-II experiment will take advantage of HyCal’s new flash-ADC data acquisition system. PRad-II is an upgraded version of the 2019 PRad experiment that this scheduled to start running in early 2026 in Hall B of Jefferson Lab. This experiment will extract the charge radius of the proton with the highest precision ever done via electron scattering. We expect an improvement by a factor of 3 to the precision of the results from the original PRad. This improvement will come from the use of the upgraded HyCal, which allows full waveforms to be saved along with several other improvements, such as using 2 GEM layers for improved tracking allowing for more precise event reconstruction. These improvements will help to address the discrepancies first seen in muonic hydrogen spectroscopy that created the Proton Radius Puzzle. It will also allow for the coverage of a ~4-order-of-magnitude range in Q², including the lowest ever reached for an electromagnetic form factor extraction to the order of 10^-5, and help understand discrepancies between the original PRad data and data from Mainz in the form factor value. This talk will briefly discuss the main goals and magnetless experimental setup of PRad-II. There will be a special focus on the testing and preliminary performance of HyCal as preparations have been made for its installation in Hall B at Jefferson Lab.