Dark Photons and Displaced Vertices at the MUonE Experiment

TL;DR

The MUonE experiment, primarily designed for muon g-2 measurements, can also effectively search for light dark photons via displaced vertex signatures, offering new sensitivity in a specific mass and coupling range.

Contribution

This paper highlights MUonE's potential as a novel probe for dark photons through displaced vertex detection, expanding its scientific scope beyond muon g-2.

Findings

Excellent sensitivity to dark photons with masses 10-100 MeV.

Detectable kinetic mixing parameters between 10^{-5} and 10^{-3}.

Potential to observe dark photon decays into electron-positron pairs.

Abstract

MUonE is a proposed experiment designed to measure the hadronic vacuum polarization contribution to muon $g-2$ through elastic $\mu-e$ scattering. As such it employs an extremely high-resolution tracking apparatus. We point out that this makes MUonE also a very promising experiment to search for displaced vertices from light, weakly-interacting new particles. We demonstrate its potential by showing how it has excellent sensitivity to dark photons in the mass range $10~\mathrm{MeV} \le m_{A'} \le 100~\mathrm{MeV}$ and kinetic mixing parameter $10^{-5} \le \epsilon e \le 10^{-3}$, through the process $\mu^{\pm}\, e^- \to \mu^{\pm}\, e^-\, A'$ followed by $A'\to e^+e^-$.