Dedicated Searches for Millicharged Particles at Intensity-Frontier Facilities: SpinQuest and SHiP

TL;DR

This study evaluates the potential of SpinQuest and SHiP experiments to detect millicharged particles, showing that proton bremsstrahlung is the dominant production mechanism and that future experiments could significantly improve current sensitivity limits.

Contribution

The paper provides a detailed analysis of mCP production mechanisms and sensitivity estimates for SpinQuest and SHiP, highlighting the dominance of proton bremsstrahlung in the sub-GeV mass range.

Findings

Proton bremsstrahlung dominates mCP production in the sub-GeV range.

Future experiments can improve sensitivity to mCP charge by up to two orders of magnitude.

Detailed simulations suggest substantial discovery potential at SpinQuest and SHiP.

Abstract

We conduct a dedicated study of searches for millicharged particles (mCPs) utilizing scintillator-based detectors at high-intensity fixed-target experiments, with particular focus on the SpinQuest and forthcoming Search for Hidden Particles experiment (SHiP) facilities. The analysis incorporates the three primary production mechanisms: meson decays, Drell-Yan processes, and proton bremsstrahlung. In particular, our updated analysis reveals that proton bremsstrahlung dominates the production rate in the sub-GeV mass regime. Detailed detector simulations and background evaluations are performed to obtain realistic sensitivity estimates. Our results demonstrate that future experiments located in the SpinQuest and SHiP facilities can achieve substantial improvements in discovery potential, enhancing sensitivity to the mCP charge parameter $\epsilon=q_{\chi}/e$ (with $q_\chi$ denoting the mCP electric charge) by up to two orders of magnitude relative to existing limits.