Probing millicharged particles with NA64 experiment at CERN

Abstract

In this note we estimate the sensitivity of the NA64 experiment to millicharged particles ($\chi$). That experimental facility is dedicated to the searching for dark sector particles in missing energy events at the CERN SPS. We consider missing momentum signatures in the $\simeq$ 100 GeV electron and muon beams and show that the later one allows to obtain more stringent bounds on the millicharge $Q_{\chi }$, which for the $\chi$ masses $100$~MeV $\le m_{\chi }\le 500$~MeV at the level $Q_{\chi }/e\lesssim O(10^{-3})-O(10^{-2})$.

Comments: 9 pages, 3 figures, version accepted for publication in PRD