Searching for A Dark Photon in the Hps Experiment

• Main Author: Paul, Sebouh Jacob
• Format: Others
• Language: English
• Published: W&M ScholarWorks 2018
• Subjects: Physics
• Online Access: https://scholarworks.wm.edu/etd/1530192707; https://scholarworks.wm.edu/cgi/viewcontent.cgi?article=1316&context=etd

The Heavy Photon Search (HPS) experiment at Jefferson Lab is designed to search for a hypothesized elementary particle called a dark (heavy) photon. Such a particle would behave as a mediator between dark matter and the Standard Model through a kinetic mixing with the Standard Model’s photon. The search is performed by scattering GeV-scale electrons off tungsten nuclei in a fixed target and looking for a resonance and/or displaced vertices amidst a background of radiative QED trident events. These background events are kinematically identical to the events in which dark photons are produced and decay into lepton pairs. Several other types of reactions take place in this experiment, such as Bethe-Heitler tridents, Moeller scattering, wide-angle bremsstrahlung and elastic scattering off the nucleus. Each of these types of background reactions are used for calibration of the detector. For one of these calibration studies, we have measured the form factors for electrons scattering elastically and nearly-elastically off a carbon target and compared these to predicted values. A resonance search, performed on 10% of the dataset taken in 2016 with a 2.306 GeV beam, shows no sign of a dark photon in the mass range 45-200 MeV. Preliminary upper limits on the square of the dark-photon’s kinetic coupling to the Standard Model photon have been set in the 10−6 − 10−5 range at 95% confidence for every mass hypothesis in this mass range.