Can millicharge be probed at future Super Tau Charm Facility via mono-$\pi^0$ searches?

TL;DR

This paper explores the potential of the future Super Tau Charm Facility to detect millicharged particles through mono-$ pi^0$ searches, providing new calculations of signal and background, and setting upper limits on millicharge.

Contribution

It introduces a novel mono-$ pi^0$ search channel at STCF for millicharged particles and computes expected signals and limits, which had not been done before.

Findings

Upper limits on millicharge can be improved for particles under 500 MeV.

Mono-$ pi^0$ searches are competitive with some past experiments.

This method offers a complementary approach to dark matter detection.

Abstract

We propose a new channel to search for millicharged particles at the future Super Tau Charm Facility (STCF) via mono-$\pi^0$ signature. For the first time, we compute the mono-$\pi^0$ signal events at the future STCF due to millicharged particle production, as well as due to standard model irreducible/reducible backgrounds. By utilizing the assumed 20 ab$^{-1}$ luminosity for each running energy with $\sqrt{s}= 2$ GeV, 4 GeV and 7 GeV, we derive the corresponding upper limits on millicharge, respectively. Via mono-$\pi^0$ searches at the future STCF with $\sqrt{s}=2$ GeV, the upper limits on millicharge can be improved than ArgoNeuT when the mass of millicharged particle is less than about 500 MeV, but are not very competitive compared to a latest derivation from a past BEBC experiment and a new SENSEI experiment. Regardless, the mono-$\pi^0$ searches could be an important complement to investigate the invisible particles, such as dark matter.