Speaker
Description
Despite being a highly sensitive probe for physics beyond the Standard Model (BSM), the anomalous magnetic moment of the tau lepton $a_\tau$ remains significantly less explored than those of other leptons. This talk presents a promising path to measure $a_\tau$ with a precision of $10^-5$, a level crucial for imposing meaningful constraints on BSM theories. Achieving this precision necessitates advancing the cross-section calculations for the process $e^+e^- \to \tau^+\tau^-$ to two-loop accuracy. Recognizing the immense challenges in measuring the full cross section at such precision, we shift our focus to exploiting specific asymmetries accessible via polarized electron beams. Concurrently, these techniques can be applied to probe the tau's electric dipole moment $d_\tau$, with the potential to enhance sensitivity down to $10^{-20} e\,{\rm cm}$. We will present first next-to-leading order results [1] implemented using the Monte Carlo integrator McMule, incorporating kinematical cuts. Furthermore, we map out the path towards next-to-next-to-leading order while addressing the attendant challenges.
[1] J. Gogniat, M. Hoferichter and Y. Ulrich, arXiv:2505.09678 [hep-ph].