Prompt A′ Resonance Search with the Heavy Photon Search Experiment

The Heavy Photon Search Experiment (HPS) at Thomas Jefferson National Accelerator Facility (JLAB) is a fixed-target experiment searching for a U(1)′ gauge boson, i.e. A′, acting as a mediator between the dark sector and the standard model. HPS searches for A′ through its visible decay to an electron-positron pair and has unique reach for visibly decaying sub-GeV mediator particles at the target (prompt A′ decay) in the form of narrow resonances in the invariant mass distribution (IMD) of electron-positron pairs. In recently published results from the HPS at JLAB 2016 engineering run, a prompt A′ decay resonance search was conducted over the e+e− IMD between 39 MeV and 179 MeV by fitting local search windows centered about each mass hypothesis and found, in agreement with other searches, an exclusion of models in this mass range with ε2 ≳ 10−5. This presentation will summarize the search methodology and results of the 2016 dataset, introduce a preliminary methodology for a procedure in development of performing global fits to the IMD of 2016, and describe how this global fitting procedure will be applied to the HPS physics run datasets collected in 2019 and 2021.