Abstract

We report the status of the Heavy Flavour Averaging Group (HFLAV) averages of the \tauτ lepton measurements We then update the latest published HFLAV global fit of the \tauτ lepton branching fractions (Spring 2017) with recent results by . We use the fit results to update the Cabibbo-Kobayashi-Maskawa (CKM) matrix element \left|V_{us}\right||Vus| measurements with the \tauτ branching fractions. We combine the direct \tauτ branching fraction measurements with indirect predictions using kaon branching fractions measurements to improve the determination of \left|V_{us}\right||Vus| using \tauτ branching fractions. The \left|V_{us}\right||Vus| determinations based on the inclusive branching fraction of \tauτ to strange final states are about 3\sigma3σ lower than the \left|V_{us}\right||Vus| determination from the CKM matrix unitarity.

Highlights

  • The τ subgroup of the Heavy Flavour Averaging Group (HFLAV) provides a global fit of the τ branching fractions, the lepton universality tests and the |Vus| determination based on τ measurements

  • A version of the HFLAV τ branching fractions fit with unitarity constraint is published on the Review of Particle Physics [2] (RPP)

  • We update the HFLAV-Tau global fit inputs with two BABAR measurements that became public in 2018 [4, 5] and we update the |Vus| determinations based on τ data

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Summary

Introduction

The τ subgroup of the Heavy Flavour Averaging Group (HFLAV) provides a global fit of the τ branching fractions, the lepton universality tests and the |Vus| determination based on τ measurements. A version of the HFLAV τ branching fractions fit with unitarity constraint is published on the Review of Particle Physics [2] (RPP). The fit results are used to test lepton universality and to compute |Vus| [1]. We update the HFLAV-Tau global fit inputs with two BABAR measurements that became public in 2018 [4, 5] and we update the |Vus| determinations based on τ data. The new results have a negligible effect on the lepton universality tests. We add to the fit input measurements of three τ branching fractions that are indirectly determined using measurements of kaon branching fractions [6], in order to improve the precision on |Vus|

New τ branching fraction measurements
Conclusions

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