Speaker
Description
Abstract The PRad-II and X17 experiments are scheduled to run in Jefferson Lab’s Hall B from November 2025 to July 2026. These experiments strive to give definite answers to long-standing questions in hadron physics. PRad-II is addressing the discrepancy in elastic electron-proton scattering at momentum transfers between 0.01 and 0.06 GeV2 that are seen between the world’s most complete data set taken with focusing magnetic spectrometers on the one side and the data set from the proton charge radius experiment at Jefferson Lab (PRad) collected with a magnetic-spectrometer-free method using a windowless hydrogen gas target. The X17 experiment is addressing a hypothetical light boson with a mass of about 17 MeV/c2 that has been discussed to explain some anomalous nuclear transition data. A search will be achieved by performing a "bump hunt" in the spectrum of electron-positron pairs produced in a thin solid-state target. The beamline and detector set-ups are shared by the two experiments with only small variations except for the two different target systems. A main component is the calorimeter HyCal for the detection of scattered electrons with a large Q2 coverage at small scattering angles (PRad-II) or for the detection of electron-positron pairs (X17). Other critical components are two planes each made of two high-resolution gas electron multiplier (GEM) coordinate detectors located in front of HyCal, and a voluminous vacuum chamber spanning the distance from the target to the detectors. All parts are currently under test or development at the University of Virginia and Jefferson Lab. Installation is planned for Summer 2025. Running the experiments for more than 200 calendar days will provide data sets with unprecedented statistics, while several measures will be in place to minimize systematic uncertainties.
