Searching for $\tau \rightarrow \mu \gamma$ lepton-flavor-violating decay at super charm-tau factory

TL;DR

This paper explores the potential to detect the rare lepton-flavor-violating decay $ au ightarrow extmu extgamma$ at the Super Charm-Tau Factory, proposing optimized event selection and deriving new constraints on new physics models.

Contribution

It introduces an optimized method for searching $ au ightarrow extmu extgamma$ decay at the CTF and sets new bounds on leptoquark model parameters based on expected data.

Findings

Projected upper limit on $Br( au ightarrow extmu extgamma)$ is about $1.9 imes 10^{-9}$.

Constraints on leptoquark couplings and masses are derived from the decay bounds.

The CTF can surpass Super-B factory in sensitivity to this decay mode.

Abstract

We investigate the possibility of searching the lepton-flavor-violating (LFV) $\tau\rightarrow \mu\gamma$ rare decay at the Super Charm-Tau Factory (CTF). By comparing the kinematic distributions of the LFV signal and the standard model (SM) background, we develop an optimized event selection criteria which can significantly reduce the background events. It is concluded that new $2 \sigma$ upper limit of about $1.9 \times 10^{-9}$ on $Br(\tau \rightarrow \mu \gamma)$ can be obtained at the CTF, which is beyond the capability of Super-B factory in searching $\tau$ lepton rare decay. Within the framework of the scalar leptoquark model, a joint constraint on $\lambda_1 \lambda_2$ and $M_{LQ}$ can be derived from the upper bound on $Br(\tau \rightarrow \mu \gamma)$. With $1000~ fb^{-1}$ data expected at the CTF, we get $\lambda_1\lambda_2 < 7.2 \times 10^{-2}~(M_{LQ} = 800~ {\rm GeV})$ and $M_{LQ} > 900~{\rm GeV}~(\lambda_1 \lambda_2 = 9 \times 10^{-2})$ at $95\%$ confidence level (C.L.).