Full angular spectrum analysis of tensor current contribution to $A_{cp}(\tau \rightarrow K_{s} \pi \nu_{\tau})$.

Lobsang Dhargyal

doi:10.31526/lhep.3.2018.03

Abstract

Babar collaboration has reported an intriguing opposite sign in the integrated decay rate asymmetry $A_{cp}(\tau \rightarrow K_{s} \pi \nu_{\tau})$ than that of SM prediction from the known $K^{0} - \bar{K^{0}}$ mixing. Babar's result deviate from the SM prediction by about 2.7$\sigma$. If the result stands with higher precision in the future experiments, the observed sign anomaly in the $A_{cp}(\tau \rightarrow K_{s} \pi \nu_{\tau})$ can most likely come only from a NP. In this work we present a full angular spectrum analysis on the contribution to $A_{cp}(\tau \rightarrow K_{s} \pi \nu_{\tau})$ coming from the tensorial term. Assuming the real part of the NP tensorial coupling is negligible compare to its imaginary part and with $A_{cp}(\tau \rightarrow K_{s} \pi \nu_{\tau})$ and $Br(\tau \rightarrow K_{s} \pi \nu_{\tau})$ as data points to fit the imaginary part of the NP coupling, we have been able to fit the result within 1$\sigma$ of the experimental values.

Highlights

The study of CP violation in tau decays has always been of much interest for beyond the Standard Model studies in the past two decades
While the Kobayashi Maskawa ansatz for CP violation within the Standard Model [1] in the quark sector has been clearly verified by the plethora of data from the B factories, this is unable to account for the observed baryon asymmetry of the Universe
Since in two pseudo scalar meson final states only vector current can contribute due to parity conservation of strong interaction, vector type of NP can contribute in general to CP violation in three or more pseudo scalar meson final states but not in two pseudo scalar meson final states such as Ksπ

Summary

INTRODUCTION

The study of CP violation in tau decays has always been of much interest for beyond the Standard Model studies in the past two decades. The key requirement in the relevant context of explaining the observed CPV in integrated τ → Ksπντ decay rate by the tensorial operator is that its coefficient CTl from Eqs (8) should be complex so that interference of the SM with this tensor amplitude gives the required CP phase. In a previous collaboration involving the author[8], we have argued that tensor type of NP may be able to explain the observed sign anomaly, in that work we have assumed that the tensor form factors are constants, but it turns out that is not the case in general and so in this work we have been able to express the tensor form factors in terms of scalar and vector form factors using Dirac equations of motion. Re(CTτ ) ≈ 0 and the sign of the complex part is opposite in Γτ+ relative to the Γτ− , the branching fraction receives no contribution from the SM and Tensorial mixing part

RESULTS

FUTURE PROSPECTS

CONCLUSIONS