Searching for lepton flavor violating interactions at future electron-positron colliders

Abstract

Lepton flavor violating interactions are absent in the standard model but are expected in various beyond standard models. In this work, the potential of the future circular electron-positron collider to probe the four fermion lepton flavor couplings via the $e^{+}e^{-}\rightarrow e^{\pm}\tau^{\mp}$ process is revisited by means of an effective field theory approach. We provide constraints at $95\%$ CL on the dimension-six Wilson coefficients including major sources of background processes and considering realistic detector effects at four expected operation energies $\sqrt{s}=157.5$, $162.5$, $240$ and $365$ GeV according to their corresponding integrated luminosities. We demonstrate that statistical combination of the results from four center-of-mass energies improves the sensitivity to the LFV couplings significantly. We compare the results with the prospects from Belle II with $50~ ab^{-1}$ and other studies at electron-positron colliders.