Millicharged particles at electron colliders

TL;DR

This paper explores the potential of electron colliders like Belle II, BESIII, BaBar, and STCF to detect millicharged particles in the MeV to GeV mass range using monophoton signals, extending the search into previously unexplored parameter space.

Contribution

It introduces a novel search strategy for millicharged particles at electron colliders and estimates their sensitivity to new parameter regions.

Findings

Electron colliders can probe millicharge $ o ext{~}10^{-1}$ for 0.5-3.5 GeV masses.

BESIII sensitivity reaches $ o ext{~}10^{-3}$ for 0.1-1.5 GeV masses.

STCF can detect millicharges $ o ext{~}10^{-4}$ for 1 MeV-1 GeV masses.

Abstract

We propose to search for millicharged particles in electron colliders operated with the center-of-mass energies at ${\cal O}$(1-10) GeV, which include Belle II, BESIII, BaBar, and also the proposed experiment STCF. We use the monophoton final state at electron colliders to probe the parameter space of millicharged particles, that is spanned by millicharge $\epsilon$ and mass $m$. We find that electron colliders have sensitivity to the previously unexplored parameter space for millicharged particles with MeV-GeV mass: $\epsilon \lesssim {\cal O}(10^{-1})$ for $0.5$ GeV $\lesssim m \lesssim 3.5$ GeV in BaBar, $\epsilon \lesssim {\cal O}(10^{-3})$ for $0.1$ GeV $\lesssim m \lesssim 1.5$ GeV in BESIII, $\epsilon \lesssim 10^{-3}-10^{-2}$ for $0.1$ GeV $\lesssim m \lesssim 4$ GeV in Belle II, and $\epsilon \lesssim {\cal O}(10^{-4})$ for $1$ MeV $\lesssim m \lesssim 1$ GeV in STCF.