Relaxing constraints on a broad dark photon

TL;DR

This paper explores how increasing the decay width of a dark photon, especially when it decays into dark matter, can relax existing experimental constraints on its parameters, notably the mixing parameter.

Contribution

It demonstrates that broader dark photon decay widths, including dark matter decay channels, significantly weaken previous exclusion limits from direct searches.

Findings

Relaxed bounds on the mixing parameter $$ with increased decay width.

Dark matter decay channels can increase the mixing parameter limit by an order of magnitude.

Existing experimental limits are sensitive to the dark photon decay width and decay modes.

Abstract

We revisit the exclusion constraints on the parameters of a narrow dark photon set by direct experimental searches. We investigate how a dark photon with a larger decay width impacts these limits, in particular, in the case where the dark photon also decays into light dark matter. As an example, taking the upper limits on the mixing parameter, $\epsilon$, reported by the CMS collaboration, we find that they could be significantly relaxed. Indeed, even a very modest coupling of the dark photon to dark matter can lead to an increase in the bound on the mixing parameter by an order of magnitude.