Speaker
Description
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 region is natural in hidden sector models of light, thermal dark matter. The $A'$ couples to the ordinary photon through kinetic mixing, which induces its 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 located at the Thomas Jefferson National Accelerator Facility 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 coupling parameter space.
HPS conducted successful engineering runs in the springs of 2015 using a 1.056 GeV, 50 nA beam and 2016 using a 2.3 GeV, 200 nA beam. This talk will present the results of a resonance search for a heavy photon using the 1165 nb$^{-1}$ (7.29 mC) of data collected during the 2015 engineering run.
