Probing Lepton Flavor Violation at Linear Electron-Positron Colliders

TL;DR

This paper investigates how future linear electron-positron colliders can detect lepton flavor violation through tau-mu pair production, using effective field theory to estimate sensitivities and explore polarization effects.

Contribution

It provides the first detailed sensitivity estimates for lepton flavor violation at ILC and CLIC, considering beam polarization and four-fermion operators within EFT.

Findings

Projected sensitivities can surpass Belle II in certain scenarios.

Beam polarization enhances tests of interaction chirality.

High energies improve sensitivity to four-fermion operators.

Abstract

The production of $\tau\mu$ pairs in electron-positron collisions offers a powerful probe of lepton flavor violation. In this work, we calculate the $e^+ e^- \to \tau \mu$ cross section within the framework of the Standard Model Effective Field Theory, allowing for arbitrary $e^+e^-$ beam polarizations. We then estimate the sensitivities of proposed future linear colliders, ILC and CLIC, to effective lepton flavor-violating interactions. The high center-of-mass energies achievable at these machines provide particularly strong sensitivity to four-fermion operators. Furthermore, the polarization of the $e^+e^-$ beams enables novel tests of the chirality structure of these interactions. We find that our projected sensitivities not only complement but in certain scenarios surpass those achievable with low-energy tau decay measurements at Belle~II.