Search for a Dark Photon in Electro-Produced $e^{+}e^{-}$ Pairs with the Heavy Photon Search Experiment at JLab

TL;DR

The Heavy Photon Search experiment at JLab conducted its first data run to detect dark photons via electron-positron pairs, setting upper limits on their coupling strength and confirming experimental readiness for future, more sensitive searches.

Contribution

First data from the Heavy Photon Search experiment at JLab searching for dark photons in the 19-81 MeV range, establishing experimental capability and setting new upper limits.

Findings

No evidence of dark photon decays was observed.

Upper limits on dark photon coupling were set at 6×10^{-6}.

Experiment demonstrated full functionality for future higher-luminosity runs.

Abstract

The Heavy Photon Search experiment took its first data in a 2015 engineering run at the Thomas Jefferson National Accelerator Facility, searching for a prompt, electro-produced dark photon with a mass between 19 and 81 MeV/$c^2$. A search for a resonance in the $e^{+}e^{-}$ invariant mass distribution, using 1.7 days (1170 nb$^{-1}$) of data, showed no evidence of dark photon decays above the large QED background, confirming earlier searches and demonstrating the full functionality of the experiment. Upper limits on the square of the coupling of the dark photon to the Standard Model photon are set at the level of 6$\times$10$^{-6}$. Future runs with higher luminosity will explore new territory.