Resonance Search for a Heavy Photon in the 2015 Engineering Run Data of the Heavy Photon Search Experiment

The Heavy Photon Search (HPS) experiment at Jefferson Lab is searching for a new $U(1)$ vector boson (``heavy photon'',``dark photon'' or $A'$) in the mass range of 20-500 MeV/c$^{2}$. An $A'$ in this mass range is theoretically favorable and may also mediate dark matter interactions. The $A'$ couples to the ordinary photon through kinetic mixing, which induces their coupling to electric charge. Since heavy photons couple to electrons, they can be produced through a process analogous to bremsstrahlung, subsequently decaying to an $e^{+}e^{-}$, which can be observed as a narrow resonance above the dominant QED trident background. For suitably small couplings, heavy photons travel detectable distances before decaying, providing a second signature. Using the CEBAF electron beam at Jefferson Lab incident on a thin tungsten target, along with a compact, large acceptance forward spectrometer consisting of a silicon vertex tracker and lead tungstate electromagnetic calorimeter, HPS is accessing unexplored regions in the mass-coupling phase space. The HPS engineering run took place in spring of 2015 using a 1.056 GeV, 50 nA beam and collected 1165 nb$^{-1}$ (7.29 mC) of data. This talk will present the results of a resonance search for a heavy photon using the engineering run data.