Spin correlations in $\tau$-lepton pair production due to anomalous magnetic and electric dipole moments

TL;DR

This paper introduces a straightforward algorithm to incorporate anomalous electric and magnetic dipole moments into simulations of tau lepton pair production, enabling detailed analysis of spin correlations and decay distributions.

Contribution

The authors develop an in-situ algorithm compatible with KKMC to efficiently simulate effects of anomalous dipole moments on tau pair events without altering generator libraries.

Findings

The algorithm accurately models the impact of dipole moments on spin correlations.

Simulated distributions show sensitivity to different anomalous coupling values.

The method facilitates experimental constraints on tau dipole moments.

Abstract

We present a simple algorithm for the calculation of event weights embedding the effects of anomalous electric and magnetic dipole moments in simulation of $e^-e^+\to \tau^-\tau^+ (n\gamma)$ events, and the subsequent decay of the $\tau$ leptons produced. The impact of these weights on the spin-correlation matrix and the total cross-section is taken into account. The algorithm is prepared to work in-situ the {\tt KKMC} Monte Carlo, without the need for introducing any external change to the generator libraries. As an example, $e^-e^+ \to \tau^-\tau^+ (n\gamma), \; \tau^- \to \rho^- \nu_\tau \to \pi^- \pi^0 \nu_\tau, \ \tau^+ \to \rho^+ \bar{\nu}_\tau \to \pi^+ \pi^0 \bar{\nu}_\tau$ events were simulated at a center-of-mass energy of 10.58 GeV. The distributions of the acoplanarity angle between the planes spanned by the $\pi^- \pi^0$ and the $\pi^+ \pi^0$ momenta of respectively $\rho^-$ and $\rho^+$ decays and in the rest-frame of the entirely visible $\rho^-\rho^+$ system, are presented for different values of the coupling constants incorporating anomalous electric and magnetic dipole moments in the $\tau^- \tau^+ \gamma$ vertex.