Search for Dark Photons with the FASER detector at the LHC

TL;DR

The FASER experiment at the LHC searched for dark photons in 2022 data, setting new constraints on their properties and also probing a U(1)$_{B-L}$ gauge boson, with no signals observed.

Contribution

First search for dark photons decaying to electron-positron pairs at the LHC using FASER, establishing world-leading constraints and exploring new parameter space.

Findings

No dark photon events observed, setting stringent limits.

Excluded new parameter space for a U(1)$_{B-L}$ gauge boson.

Provided the most restrictive bounds on dark photon couplings in the studied mass range.

Abstract

The FASER experiment at the LHC is designed to search for light, weakly-interacting particles produced in proton-proton collisions at the ATLAS interaction point that travel in the far-forward direction. The first results from a search for dark photons decaying to an electron-positron pair, using a dataset corresponding to an integrated luminosity of 27.0 fb$^{-1}$ collected at center-of-mass energy $\sqrt{s} = 13.6$ TeV in 2022 in LHC Run 3, are presented. No events are seen in an almost background-free analysis, yielding world-leading constraints on dark photons with couplings $\epsilon \sim 2 \times 10^{-5} - 1 \times 10^{-4}$ and masses $\sim$ 17 MeV - 70 MeV. The analysis is also used to probe the parameter space of a massive gauge boson from a U(1)$_{B-L}$ model, with couplings $g_{B-L} \sim 5 \times 10^{-6} - 2 \times 10^{-5}$ and masses $\sim$ 15 MeV - 40 MeV excluded for the first time.