Probing millicharged particles with NA64 experiment at CERN

TL;DR

This paper evaluates the NA64 experiment's potential to detect millicharged particles, showing that muon beams provide more stringent bounds on their charge for certain mass ranges.

Contribution

It estimates the sensitivity of the NA64 experiment to millicharged particles using missing momentum signatures in electron and muon beams, highlighting the improved bounds with muon beams.

Findings

Muon beams yield more stringent bounds on millicharge.

Bounds on millicharge are $Q_{ ext{chi}}/e \\lesssim O(10^{-3}) - O(10^{-2})$ for masses 100-500 MeV.

NA64 can probe new parameter space for millicharged particles.

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 $\leq m_{\chi} \leq 500$~MeV at the level $ Q_{\chi}/e\lesssim O(10^{-3}) - O(10^{-2})$.