Matthew Solt (Stanford U) “The Heavy Photon Search Experiment

Abstract:

The Heavy Photon Search (HPS) experiment is a fixed target experiment at Jefferson Lab searching for a new dark-force mediator called a heavy photon (or dark photon or A’). A heavy photon is a hypothetical U(1) vector boson that couples to the Standard Model photon through kinetic mixing, and thus can be produced in a process analogous to bremsstrahlung by an electron beam incident on a dense target. If kinematically allowed, subsequent decays into e+e- pairs can be detected by the HPS detector – a compact, large acceptance spectrometer consisting of a silicon vertex tracker and lead-tungstate electromagnetic calorimeter. For large couplings, heavy photons would appear as a resonance peak in the invariant mass spectrum on top of a large QED background. For sufficiently small couplings, heavy photons are long-lived and would appear as decay vertices displaced from the target beyond a prompt QED background. In this talk, I will discuss the motivation for heavy photons and the HPS detector. I will then focus on the displaced vertex analysis and discuss the results from our engineering in 2015 (1.06 GeV beam energy), the ongoing analysis of the engineering run in 2016 (2.3 GeV beam energy), and finally the upgrades and commissioning of our most recent physics run in 2019 (4.55 GeV beam energy).