CP Violation in \tau ->\nu\pi K_S and D->\pi K_S: The Importance of K_S-K_L Interference

TL;DR

This paper highlights the significance of K_S-K_L interference effects in CP asymmetry measurements in tau and D meson decays involving K_S, showing that experimental timing and interference are crucial for accurate results.

Contribution

It emphasizes the importance of K_S-K_L interference in CP asymmetry measurements, which has been previously overlooked, affecting the interpretation of experimental data.

Findings

Interference between K_S and K_L amplitudes significantly impacts CP asymmetry measurements.

Measured asymmetries depend on decay time integration and experimental setup.

Proper accounting of interference effects is essential for accurate CP violation analysis.

Abstract

The $B$-factories have measured CP asymmetries in the $\tau\to\pi K_S\nu$ and $D\to K_S\pi$ modes. The $K_S$ state is identified by its decay to two pions at a time that is close to the $K_S$ lifetime. Within the Standard Model and many of its extensions, the asymmetries in these modes come from CP violation in $K^0-\bar{K}^0$ mixing. We emphasize that the interference between the amplitudes of intermediate $K_S$ and $K_L$ is as important as the pure $K_S$ amplitude. Consequently, the measured asymmetries depend on the times over which the relevant decay rates are integrated and on features of the experiment.