Search for CP violation in tau -> K^0_S pi nu_tau decays at Belle

TL;DR

This study searches for CP violation in tau decays to K^0_S pi nu_tau using Belle data, finding no significant asymmetry and setting improved limits on CP violation parameters.

Contribution

First measurement of CP violation in tau -> K^0_S pi nu_tau decays with enhanced sensitivity, improving previous limits by an order of magnitude.

Findings

No evidence of CP violation detected.

Limits on Im(eta_S) are |Im(eta_S)|<0.026 at 90% CL.

Results improve upon previous constraints by tenfold.

Abstract

We report on a search for CP violation in tau -> K^0_S pi nu_tau decays using a data sample of 699 fb^{-1} collected in the Belle experiment at the KEKB electron-positron asymmetric-energy collider. The CP asymmetry is measured in four bins of the invariant mass of the K^0_S pi system and found to be compatible with zero with a precision of O(10^{-3}) in each mass bin. Limits for the CP violation parameter Im(eta_S) are given at a 90 % confidence level. These limits are |Im(eta_S)|<0.026 or better, depending on the parameterization used to describe the hadronic form factors and improve upon previous limits by one order of magnitude.