A new experiment to search for hidden sector particles in the 3-60 MeV range using the PRad experimental setup*

A new experiment will search the 3-60 MeV mass region for hidden sector particles produced through a Bremsstrahlung-like process. This experiment is unique in that it will detect all final-state particles, will be sensitive to both charged and neutral decay products, and will have both high-resolution energy and position information for charged decay products. Two beam energies will be used to suppress “false bumps” from kinematical reflections from known physics processes. Our search will be able to resolve the hypothetical X17 anomaly seen in two measurements at the ATOMKI accelerator. This experiment will use the PRad experimental setup in Hall B at Jefferson Lab. The setup consists of a 1µm Tantalum target that is 7.5m upstream of two GEM planes separated by 0.1m and the HyCal calorimeter. New GEM planes will allow for tracking of the recoil electron and charged decay products to reduce beam-related backgrounds. This experiment will have a coupling constant, ε², sensitivity from 7.2×10^-8 to 5.9×10^-9. The proposal was brought to JLab PAC49 and is now a conditionally-approved experiment.