Probing lepton flavor violation at Circular Electron-Positron Colliders

Abstract

Abstract Lepton flavor violation is one of the cleanest probes of physics beyond the standard model. In this work, we explore the sensitivity of the process e + e − → τμ to new physics above the TeV scale at the proposed circular electron-positron colliders FCC-ee and CEPC. We compute the e + e − → τμ cross-section in the Standard Model Effective Field Theory and assess the relevant backgrounds. We compare our sensitivity projections to existing and expected constraints from tau decays and Z decays and find that the future electron-positron colliders provide competitive probes of new physics. We highlight the complementarity of searches for resonant e + e − → Z → τμ production on the Z pole and searches for non-resonant e + e − → τμ at higher center-of-mass energies.

Keywords

• Lepton Flavour Violation (charged)
• SMEFT