Status of the Hadronic Tau Determination of V_us

TL;DR

This paper updates the determination of the CKM matrix element |V_{us}| from hadronic tau decay data, incorporating recent experimental results and sum rule analyses, revealing a significant deviation from unitarity expectations.

Contribution

It provides a comprehensive update on |V_{us}| extraction using new experimental data and advanced sum rule techniques, highlighting a persistent discrepancy with unitarity.

Findings

Results are consistent across different sum rule methods.

|V_{us}| is approximately 3 sigma below unitarity expectations.

The discrepancy suggests potential new physics or the need for further investigation.

Abstract

We update the extraction of |V_{us}| from hadronic tau decay data in light of recent BaBar and Belle results on the branching fractions of a number of important strange decay modes. A range of sum rule analyses is performed, particular attention being paid to those based on "non-spectral weights", developed previously to bring the slow convergence of the relevant integrated D=2 OPE series under improved control. Results from the various sum rules are shown to be in good agreement with one another, but ~3 sigma below expectations based on 3-family unitarity. Important avenues for future study are briefly discussed.