Electroproduced Prompt A′ Resonance Search Techniques 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 can probe

sub-GeV mediator particles visibly decaying 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

demonstrate an improved methodology for the resonance search centered on global functional form background modeling of the

IMDs from the 2015 and 2016 engineering runs, show combined reach from these data sets, and preliminarily describe how this

global fitting procedure and a multivariate gaussian blinding procedure will be applied to the HPS physics run datasets

collected in 2019 and 2021. Additionally, this presentation will introduce recent collaborative efforts into novel

background modeling using a machine learning technique known as Gaussian Process Regression and compare the performance to

that of functional form fitting.