Search for light Dark Sectors with GeV Muon Beams

TL;DR

This paper explores the potential of high-intensity muon beam experiments to detect light dark matter mediators, specifically a $Z'$ boson, using a novel detection method and machine learning background suppression.

Contribution

It introduces a new experimental approach using silicon detectors and BDT classifiers to search for light dark matter mediators in muon scattering experiments.

Findings

Can probe $Z'$ bosons in the 10 MeV mass range with improved sensitivity.

Nearly three orders of magnitude sensitivity enhancement with a 160 GeV muon beam at CERN.

Effective background suppression using trained BDT classifiers.

Abstract

Sub-GeV light dark matter often requires new light mediators, such as a dark $Z$ boson in the $L_\mu - L_\tau$ gauge theory. We study the search potential for such a $Z^\prime$ boson via the process $\mu e^- \to \mu e^- X$, with $X$ decaying invisibly, in a muon on-target experiment using a high-intensity 1-10 GeV muon beam from facilities such as HIAF-HIRIBL. Events are identified by the scattered muon and electron from the target using silicon strip detectors in a single-station telescope system. Backgrounds are suppressed through a trained boosted decision tree (BDT) classifier, and activity in downstream subdetectors remains low. This approach can probe a $Z^\prime$ boson in the 10 MeV mass range with improved sensitivity. Nearly three orders of magnitude improvement is achievable with a full multi-telescope station system employing a 160 GeV muon beam at CERN, such as in the MUonE experiment.