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HFLAV $τ$ branching fractions fit and measurements of Vus with $τ$ lepton data

Alberto Lusiani

SciPost Phys. Proc. 1, 001 (2019) · published 18 February 2019

Proceedings event

The 15th International Workshop on Tau Lepton Physics


We report the status of the Heavy Flavour Averaging Group (HFLAV) averages of the $\tau$ lepton measurements We then update the latest published HFLAV global fit of the $\tau$ lepton branching fractions (Spring 2017) with recent results by BABAR. We use the fit results to update the Cabibbo-Kobayashi-Maskawa (CKM) matrix element Vus measurements with the $\tau$ branching fractions. We combine the direct $\tau$ branching fraction measurements with indirect predictions using kaon branching fractions measurements to improve the determination of Vus using $\tau$ branching fractions. The Vus determinations based on the inclusive branching fraction of $\tau$ to strange final states are about $3\sigma$ lower than the Vus determination from the CKM matrix unitarity.

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