Status and progress of the HFLAV-Tau group activities

We report the status and progress of the Heavy Flavour Averaging Group work on the global fit of tau lepton branching fractions, on the lepton universality tests and on the measurement of the Cabibbo-Kobayashi-Maskawa matrix element |Vus| using tau lepton measurements. We also review the prospects for improving the precision of the |Vus| measurement.Comment: 6 pages, 2 figures, contribution to the proceedings of the International Workshop on e+e- collisions from Phi to Psi 2017, Mainz, Germany Revision v2: updated the text to reflect the revision arXiv:1702.01767v2 [hep-ph] published as Phys. Lett. B781, 206 (2018

Experimental Review on Lepton Universality and Lepton Flavour Violation tests at the B-factories

Since 1999, the B-factories collaborations BABAR and Belle have accumulated and studied large samples of tau lepton pairs. The experimental results on Lepton Universality checks and Lepton Flavour Violation searches are reported.Comment: 11 pages, 2 figures, 1 table (To be sumitted to the proceedings of the Kaon International Conference 2007

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

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.Comment: Proceedings of the 15th International Workshop on Tau Lepton Physics (Tau 2018). SciPost editorial revisions applied. Fixed radiative correction that was erroneously including an isospin-breaking correction, fixed one formula, corrected a few typo

Improved determination of |Vus| with τ decays

|Vus| is computed using the exclusive τ lepton branching fractions B(τ− → K−ντ) and B(τ− → π−ντ) and using the inclusive τ branching fraction to all “strange” final states, B(τ− → Xs−ντ), computed as the sum of all the relevant exclusive branching fractions. Assuming the Standard Model, the kaon branching fractions measurements B(K+ → `+ν`) and B(K+ → `+π0ν`) with ` = e, μ are used to improve the experimental determination of B(τ− → Xs−ντ) and |Vus|

Measurements of |Vus| and Searches for Violation of Lepton Universality and CPT in Tau Decays at BaBar

Using data collected with the BaBar detector at PEP-II at SLAC, we report on several tau lepton measurements that are used to determine the modulus of the Cabibbo-Kobayashi-Maskawa matrix element Vus, and to check the Standard Model predictions of lepton universality and CPT conservation.Comment: To appear in the proceedings of the 2010 ICHEP meeting, 6 pages, 1 figur

Predicting the tau strange branching ratios and implications for V_{us}

Hadronic tau decays provide several ways to extract the Cabbibo-Kobashi-Maskawa (CKM) matrix element V_{us}. The most precise determination involves using inclusive tau decays and requires as input the total branching ratio into strange final states. Recent results from B-factories have led to a discrepancy of about 3.4 sigma from the value of V_{us} implied by CKM unitarity and direct determination from Kaon semi-leptonic modes. In this paper we predict the three leading strange tau branching ratios, using dispersive parameterizations of the hadronic form factors and taking as experimental input the measured Kaon decay rates and the tau -> K pi nu_tau decay spectrum. We then use our results to reevaluate V_{us}, for which we find |V_{us}|=0.2207 \pm 0.0027, in better agreement with CKM unitarity.Comment: 20 pages, 3 figure