Measurement of the Michel Parameters ξ′ , ξ′′ , η′′ , α′/A , and β′/A in the τ−→μ−ν¯μντ Decay at the Future Super Charm-Tau Factory

Bulletin of the Lebedev Physics Institute. 2023. Vol. 50. No. 4. P. 144–149.

Bodrov D., Pakhlov P.

A method for measuring all Michel parameters describing the daughter muon polarization in the tau(-) -> mu(-) (nu(mu)) over bar nu(tau) decay, i.e., xi', xi", eta", alpha'/A, and beta'/A, is discussed. The application of the method to the future Super Charm-Tau Factory experiment is considered. The statistical uncertainties expected by the full data statistics (10 ab(-1)) are estimated as sigma(xi') = 0.006, sigma(xi'') = 0.03, sigma(eta'') = 0.02, sigma(alpha'/A) = 0.014, and sigma(beta'/A) = 0.007. On their basis, upper limits on the coupling constants of interactions beyond the Standard Model are estimated. The New Physics scenario is considered, which can be reliably detected if the estimated accuracy of the xi' parameter measurement is achieved.

Keywords: Michel parameters, tau-lepton physics, Super charm-tau Factory

Publication based on the results of: Development of new methods for searching for physics beyond the Standard Model in experiments at the Super Charm-Tau Factory and Belle at the KEKB B-Factory (2023)