On direct observation of millicharged particles at $c$-$\tau$ factories and other $e^+e^-$-colliders

TL;DR

This paper proposes a novel method to detect millicharged particles directly via energy deposits in trackers at $c$-$ au$ factories, potentially probing lower charges and mass ranges than traditional missing energy searches.

Contribution

It introduces a new direct detection technique for millicharged particles at $e^+e^-$ colliders, especially effective for non-relativistic MCPs and in mass regions inaccessible to existing methods.

Findings

Can probe MCP charges down to 3×10^{-3} of electron charge.

Effective for MCP masses around 5 MeV near each beam energy.

Potentially background-free searches at $c$-$ au$ factory.

Abstract

Hypothetical particles with tiny electric charges (millicharged particles or MCPs) can be produced in electron-positron annihilation if kinematically allowed. Typical searches for them at $e^+e^-$ colliders exploit a signature of a single photon with missing energy carried away by the undetected MCP pair. We put forward an idea to look alternatively for MCP energy deposits inside a tracker, which is a direct observation. The new signature is relevant for non-relativistic MCPs, and we illustrate its power on the example of the $c$-$\tau$ factory, where we argued that the corresponding searches may be background-free. We find that it can probe the MCP charge down to $3\times10^{-3}$ of the electron charge for the MCP masses in ${\cal O}(5)$ MeV vicinity of each energy beam value where the factory will collect a luminosity of 100 fb$^{-1}$ in one year. This mass region is unreachable with the searches for missing energy and single photon.