Linearly Polarized Photon Fusion as a Precision Probe of the Tau Lepton Dipole Moments at Lepton Colliders

Abstract: We present a comprehensive investigation into the anomalous magnetic dipole moment ($a_\tau$) and electric dipole moment ($d_\tau$) of the $\tau$ lepton using the $\gamma\gamma \to \tau<sup>+\tau<sup>-$ 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 $\cos2\phi$, $\sin2\phi$, and $\cos4\phi$ azimuthal asymmetries to precisely probe the $\tau$ lepton's electromagnetic structure. Our analysis significantly enhances the precision of $a_\tau$ constraints, yielding $$\mathrm{Re}(a_\tau) \in [-4.5, 6.9] \times 10<sup>{-3}$$ at $2\sigma$ confidence level. This represents an order-of-magnitude improvement over existing experimental limits and 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.