Theoretical progress on the V_us determination from tau decays

TL;DR

This paper discusses theoretical advancements in precisely determining the CKM matrix element V_us from tau lepton decays, highlighting recent experimental data and potential for improved accuracy with future high-statistics measurements.

Contribution

It presents a theoretical framework for extracting V_us from tau decays with small SU(3)-breaking corrections and analyzes recent experimental results for improved precision.

Findings

V_us can be determined with competitive accuracy from tau decays.

Recent measurements imply V_us=0.2165 with combined experimental and theoretical uncertainties.

High-statistics data from B factories can significantly reduce the uncertainty in V_us.

Abstract

A very precise determination of V_us can be obtained from the semi-inclusive hadronic decay width of the tau lepton into final states with strangeness. The ratio of the Cabibbo-suppressed and Cabibbo-allowed tau decay widths directly measures (V_us/V_ud)^2, up to very small SU(3)-breaking corrections which can be theoretically estimated with the needed accuracy. Together with previous LEP and CLEO data, the recent measurements by Babar and Belle of some Cabibbo-suppressed tau decays imply V_us= 0.2165 +- 0.0026_exp +- 0.0005_th, which is already competitive with the standard extraction from K_l3 decays. The uncertainty is largely dominated by experimental errors and should be easily reduced with the high statistics of the B factories, providing the most accurate determination of this parameter. A 1% experimental precision on the Cabibbo-suppressed tau decay width would translate into a 0.6% uncertainty on V_us.