Search for charged lepton flavor violation in J/ψ decays at BESIII

The observation of any charged lepton flavor violation (CLFV) process would be a clear signal of new physics beyond the Standard Model. Various decay modes, including lepton ( μ , τ ) decays, pseudoscalar meson ( K , π ) decays, vector meson ( ϕ , J / ψ , Υ ) decays, and Higgs decays, have been explored to detect CLFV. Focusing on the search for CLFV at the τ -charm region, the results of the search for J / ψ → eτ / eμ using the 10 billion J / ψ events collected by the BESIII experiment are presented. The upper limits (ULs) at the 90% confidence level are ℬ( J / ψ → e ± τ ∓ ) < 7.5 × 10 -8 and ℬ( J / ψ → e ± μ ∓ ) < 4.5 × 10 -9 , respectively. Improving the previously published limits by two orders of magnitudes, the results are the most stringent CLFV searches in heavy quarkonium system.