Sensitivity study of searching for τ− → γμ− at HIEPA

The charged lepton flavor violation process is a clean and sensitive probe of new physics beyond the Standard Model. A sensitivity study is performed to the process τ−→ γμ− based on a 3 fb−1 inclusive Monte Carlo sample of e+e− collisions at a center-of-mass energy of 4.26 or 4.6 GeV, in the framework of the BESIII software system. The 90% confidence level upper limits on ℬ(τ−→γμ−) are estimated assuming no signal is produced. We also obtain the sensitivity on ℬ(τ−→γμ−) as a function of the integrated luminosity, to serve as a reference for the HIEPA being proposed in China. It is found that 6.34 ab−1 are needed to reach the current best upper limit of 4.4 × 10−8 and about 2510 ab−1 are needed to reach a sensitivity of 10−9 if the detector design is similar to that of BESIII.