Sensitivity Study of the Tau Lepton Electric Dipole Moment at the Super Tau-Charm Facility

Abstract

This study investigates the intrinsic electric dipole moment (EDM) of the $\tau$ lepton, which is an important quantity in the search for physics beyond the Standard Model (BSM). In preparation for future measurements at the Super Tau-Charm Facility (STCF), we employ Monte Carlo simulations of the $e^{+}{e}^{-}\to {\tau }^{+}{\tau }^{-}$ process and optimize the analysis methodology for EDM extraction. Machine learning techniques are implemented to efficiently identify signal events (${\tau }^{\pm }\to {\pi }^{\pm }{\pi }^0{\nu }_{\tau }$), which result in a significant improvement in signal-to-noise ratio. Our optimized event selection algorithm achieves $80.0\%$ signal purity with $6.3\%$ efficiency. We develop an analytical approach for $\tau$ lepton momentum reconstruction and derive the squared spin density matrix along with optimal observables, which maximize the sensitivity to $d_{\tau }$. The relationship between these observables and the EDM is established with the estimated sensitivity of $|d_{\tau }|<3.89\times 10^{-18}e\cdot \mathrm{cm}$ at a $68\%$ confidence level. These results provide a foundation for future experimental measurements of the $\tau$ lepton EDM in STCF experiments.

arXiv comment20 pages, 8 figures

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