Search for light Dark Sectors with GeV Muon Beams

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.

Comments: 8 pages, 7 figures