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Spin effects in the tau-lepton pair induced by anomalous magnetic and electric dipole moments

A. Yu. Korchin

Abstract

The possible anomalous New Physics contributions to magnetic and electric dipole moments of the $τ$ lepton have brought renewed interest in studying $τ$-pair production at energies of the LHC and future colliders. We discuss effects of electromagnetic and weak dipole moment contributions to the $τ$-lepton polarization and $ττ$ spin correlations in the $γγ\to τ^-τ^+$ and $q \bar{q} \to τ^- τ^+$ processes. Such processes have been observed in $pp$ and PbPb collisions in the LHC experiments. Extensions of the Standard Model amplitudes for $γγ\to τ^-τ^+$ and $q \bar{q} \to τ^- τ^+$ processes, which include dipole moments of the $τ$ lepton, are implemented in the TauSpinner Monte Carlo program. A few examples of signatures of $ττ$ spin correlations and $τ$-lepton dipole moments in observables are presented.

Spin effects in the tau-lepton pair induced by anomalous magnetic and electric dipole moments

Abstract

The possible anomalous New Physics contributions to magnetic and electric dipole moments of the lepton have brought renewed interest in studying -pair production at energies of the LHC and future colliders. We discuss effects of electromagnetic and weak dipole moment contributions to the -lepton polarization and spin correlations in the and processes. Such processes have been observed in and PbPb collisions in the LHC experiments. Extensions of the Standard Model amplitudes for and processes, which include dipole moments of the lepton, are implemented in the TauSpinner Monte Carlo program. A few examples of signatures of spin correlations and -lepton dipole moments in observables are presented.
Paper Structure (4 sections, 18 equations, 3 figures)

This paper contains 4 sections, 18 equations, 3 figures.

Table of Contents

  1. Introduction
  2. Magnetic and electric dipole form-factors and moments
  3. Results and discussion
  4. Summary

Figures (3)

  • Figure 1: Spin-correlation effects in $\gamma \gamma \to \tau \tau$ for $\tau$-decay channels: $\tau^-\to \rho^- \nu_\tau \to \pi^- \pi^0 \nu_\tau$ and $\tau^+ \to \rho^+ \bar{\nu}_\tau \to \pi^+ \pi^0 \bar{\nu}_\tau$. The ratio (SM without spin correlations)/(SM with spin correlations) is shown. The figure is taken from Ref. Korchin:2025vzx.
  • Figure 2: Kinematical distributions in the $\gamma \gamma \to \tau \tau$ process for $\tau$-lepton decays $\tau^\pm \to \rho^\pm \nu_\tau \to \pi^\pm \pi^0 \nu_\tau$. Compared are the calculations in SM and SM+NP with the sets: $A = 0.002, \, 0.005, \, 0.02$, $B = 0$ (left column) and $A = 0.0$, $B = 0.002, \, 0.005, \, 0.02$ (right column). The figure is taken from Ref. Korchin:2025vzx.
  • Figure 3: Distribution of several observables (see the text) for the $q \bar{q} \to \tau \tau$ process. Compared are the SM predictions (black open circles) for $X=Y=0$ and NP ones (red and blue triangles) for $X=0.1$ or $Y=0.1$. Both $\tau$ leptons decay into the $\tau^\pm \to \rho^{\pm} \nu_\tau \to \pi^\pm \pi^0 \nu_\tau$ channels. The figure is taken from Ref. Korchin:2025sui.