Result of T-violating muon polarization measurement in the $K^+ \to \pi^0 \mu^+ \nu$ decay

TL;DR

This paper reports an improved experimental limit on T-violating muon polarization in kaon decay, providing constraints on new physics beyond the Standard Model through precise measurements.

Contribution

The study presents the most stringent limit to date on T-violation in $K^+ o \pi^0 \mu^+ u$ decay using stopped kaons at KEK, refining previous bounds.

Findings

Measured muon polarization $P_T$ with improved precision.

Set a new upper limit on $|P_T|$ at 0.0050 (90% CL).

Constrained the T-violating parameter Im$\xi$ to less than 0.016 (90% CL).

Abstract

A search for T-violating muon polarization in the $K^+ \to \pi^0 \mu^+\nu$ decay has been performed at KEK using stopped kaons. A new improved limit was obtained, $P_T= -0.0017 \pm 0.0023 (stat) \pm 0.0011 (syst)$, corresponding to a 90 % confidence limit of $| P_T| < 0.0050$. The T-violating parameter was also determined to be Im$\xi = -0.0053 \pm 0.0071 (stat) \pm 0.0036 (syst)$, and $|{rm Im}\xi| < 0.016$ (90 % CL).