New tensor interaction as the source of the observed CP asymmetry in $\tau \to K_{S}\pi\nu_{\tau}$

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 K0 - $\bar{K0}$ 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 some new physics occurring possibly in both hadronic as well as leptonic sectors. In this work, we will give an improved analysis of our previous work where we have illustrated that, while non-standard scalar or vector/axial-vector interactions will not contribute to the observed asymmetry in the integrated decay rate, a new tensor interaction can explain the observed anomaly. Assuming the real part of the new 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.