LAUSR

In this note we estimate the sensitivity of the NA64 experiment currently searching for dark sector particles in missing energy events at the CERN SPS to millicharged particles ($\chi$). We consider searches with 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 $100~MeV \leq m_{\chi} \leq 500~MeV$ at the level $ Q_{\chi}/e\lesssim O(10^{-3}) - O(10^{-2})$.