Exploring Optimal Sensitivity of Lepton Flavor Violating Effective Couplings at the $e^+e^-$ Colliders

TL;DR

This paper investigates the potential to detect lepton flavor violation at future $e^+e^-$ colliders using SMEFT, focusing on tau production with electron/muon, and employs optimal observable techniques to estimate sensitivities.

Contribution

It introduces a detailed analysis of LFV sensitivities at future colliders using the SMEFT framework and optimal observable methods, considering beam polarization effects.

Findings

Sensitivity of flavor-violating couplings can be enhanced by an order of magnitude at 3 TeV colliders.

Optimal observable technique improves the estimation of coupling sensitivities.

Beam polarization and background interplay are crucial for sensitivity enhancement.

Abstract

We analyze lepton flavor violation (LFV) using the Standard Model Effective Field Theory (SMEFT) framework at the future lepton colliders. Our focus is on the associated production of tau lepton with electron/muon at the electron-positron ($e^+e^-$) colliders, related to four-Fermi SMEFT effective operators. In accordance with the upper limits on effective couplings from lepton flavor violating tau decays, we conduct a cut-based analysis to achieve sufficient signal significance. We utilize the optimal observable technique (OOT) to estimate the optimal sensitivity of the effective couplings. The impact of electron beam polarization and the interplay of signal and background in enhancing the optimal sensitivity of the effective couplings are discussed in detail. We find that the sensitivity of flavor-violating effective couplings is enhanced by order of one for 3 TeV center-of-mass (CM) energy and 1000 $\rm{fb}^{-1}$ integrated luminosity at the $e^+e^-$ colliders.