Search for CP Violation in $\tau\to \pi\pi^{0}\nu_{\tau}$ Decay

TL;DR

This study searches for CP violation in tau decays to pi pi0 nu_tau using a large data sample, finding no evidence but setting limits on CP-violating parameters within a scalar exchange model.

Contribution

It provides the first experimental limits on CP violation parameters in tau decays within a scalar exchange framework using correlated decay analysis.

Findings

No evidence of CP violation was observed.

Limits on the imaginary part of the scalar coupling parameter were established.

The analysis constrains new physics models involving scalar exchanges in tau decays.

Abstract

We search for CP non-conservation in the decays of tau leptons produced via $e^+ e^-$ annihilation at $\sqrt{s}\sim$ 10.6 GeV. The method uses correlated decays of pairs of tau leptons, each decaying to the $\pi \pi^0 \nu_{\tau}$ final state. The search is done within the framework of a model with a scalar boson exchange. In an analysis of a data sample corresponding to 12.2 million produced tau pairs collected with the CLEO detector, we find no evidence of violation of CP symmetry. We obtain a limit on the imaginary part of the coupling constant parameterizing the relative contribution of diagrams that would lead to CP violation to be $-0.046 <\Im(\Lambda) < 0.022$ at 90% C.L. This result provides a restriction on CP non-conservation in the tau lepton decays. As a cross check, we study the decay angular distribution and perform a model-independent search for a CP violation effect of a scalar exchange in single $\tau\to \pi\pi^0\nu_\tau$ decays. The limit on the imaginary part of the $\tau$ scalar coupling is $-0.033 < \Im(\Lambda) < 0.089$ at 90% C.L.