Linearly polarized photon fusion as a precision probe of the tau lepton dipole moments at lepton colliders

We present a comprehensive investigation into the anomalous magnetic dipole moment ( a τ ) and electric dipole moment ( d τ ) of the τ lepton using the γ γ → τ + τ − process at future lepton colliders, with the Super Tau-Charm Facility serving as a benchmark. By employing transverse-momentum-dependent factorization, we introduce novel observables derived from cos 2 ϕ , sin 2 ϕ , and cos 4 ϕ azimuthal asymmetries to precisely probe the τ lepton’s electromagnetic structure. Our analysis significantly enhances the precision of a τ constraints within the photon-photon fusion process, yielding Re ( a τ ) ∈ [ − 4.6 , 7.0 ] × 10 − 3 at the 2 σ confidence level, which approaches the precision of the Standard Model prediction. These findings highlight the considerable potential of azimuthal asymmetry measurements for high-precision determinations of fundamental particle properties at future lepton colliders.