Gas Electron Multiplier (GEM) Tracker for PRad-II Experiment at Jefferson Lab

The PRad-II experiment at Jefferson Lab aims to resolve the proton charge radius puzzle through ultra-precise measurements of electron-proton scattering at small scattering angles (θₑ = 0.5° to 7.0°) and in an unprecedentedly low momentum transfer region (Q² = 6×10⁻⁵ to 6×10⁻² GeV²). Building on techniques used in the original PRad experiment conducted at JLab in 2016, PRad-II introduces several key upgrades—including two layers of large-area Gas Electron Multiplier (GEM) detectors for tracking capability, a fully upgraded data acquisition and readout system, and new scintillating detectors—with the goal of reducing the uncertainty in the extracted proton charge radius by a factor of three compared to PRad. The use of two GEM tracking layers in PRad-II will reduce uncertainty in GEM detection efficiency and significantly improve vertex reconstruction, non-target background rejection, and Q² resolution. This presentation will focus on the development and fabrication of the GEM tracking system for the PRad-II experiment, as well as the evaluation of uncertainty in GEM tracking efficiency based on simulated data for the PRad-II configuration. We will also present the upgraded MPD/VTP-based readout architecture, capable of handling event rates up to 25 kHz from the GEM detectors.