Searching for Prompt and Long-Lived Dark Photons in Electro-Produced $e^+e^-$ Pairs with the Heavy Photon Search Experiment at JLab

TL;DR

The HPS experiment at JLab searched for prompt and long-lived dark photons in electron-positron pairs, finding no evidence but setting limits on their properties, and plans to explore new parameter space with future data.

Contribution

First displaced vertex search results from HPS, providing new constraints on dark photons and outlining future high-luminosity data runs for expanded exploration.

Findings

No evidence of prompt dark photons in 39-179 MeV range.

No excess signal for displaced vertices between 60-150 MeV.

Set limits on dark photon coupling strength.

Abstract

The Heavy Photon Search experiment (HPS) at the Thomas Jefferson National Accelerator Facility searches for electro-produced dark photons. We report results from the 2016 Engineering Run consisting of 10608/nb of data for both the prompt and displaced vertex searches. A search for a prompt resonance in the $e^+e^-$ invariant mass distribution between 39 and 179 MeV showed no evidence of dark photons above the large QED background, limiting the coupling of {\epsilon}^2 {\geq} 10^-5, in agreement with previous searches. The search for displaced vertices showed no evidence of excess signal over background in the masses between 60 and 150 MeV, but had insufficient luminosity to limit canonical heavy photon production. This is the first displaced vertex search result published by HPS. HPS has taken high-luminosity data runs in 2019 and 2021 that will explore new dark photon phase space.