Publications

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• $τ$ lepton mass measurement at BESIII

  Jianyong Zhang on behalf of BESIII collaboration

  SciPost Phys. Proc. 1, 004 (2019) · published 18 February 2019 | Toggle abstract · pdf

  In order to obtain the mass of $\tau$ lepton at BESIII precisely, a beam energy measurement system was built at BEPCII. A scenario for high precision $\tau$ mass measurement was put forth before data taken. More than 130 $pb^{-1}$ $\tau$ mass scan data were collected in April 2018, and the uncertainty of $m_{\tau}$ is expected to be less than 100 keV.

  1 citation

• Prospects for $\tau$ lepton physics at Belle II

  Michel Hernandez Villanueva on behalf of the Belle II collaboration

  SciPost Phys. Proc. 1, 003 (2019) · published 18 February 2019 | Toggle abstract · pdf

  The Belle II experiment is an upgrade of the Belle detector and will operate at the SuperKEKB energy-asymmetric $e^+e^-$ collider. The accelerator has already successfully completed the first phase of commissioning and first electron positron-collisions in Belle II were observed in April 2018. The design luminosity of SuperKEKB is 8x10$^{35}$ cm$^{-2}$s$^{-1}$ and the Belle II experiment aims to record 50 ab$^{-1}$ of data, a factor of 50 more than the Belle experiment. Belle II has a broad program of $\tau$ physics, in particular, precision measurements of Standard Model parameters and searches of lepton flavor and lepton number violations (LFV and LNV), benefiting from the large cross-section of the pairwise $\tau$ lepton production in $e^+e^-$ collisions. In this talk, we will review the $\tau$ lepton physics program of Belle II.

  1 citation

• Latest Belle results on Tau decays

  Yifan Jin, Denis Epifanov, Hiroaki Aihara

  SciPost Phys. Proc. 1, 002 (2019) · published 18 February 2019 | Toggle abstract · pdf

  We present preliminary results of a latest measurement at Belle, the branching fraction of rare tau decay, $\tau^- \rightarrow \pi^- \nu_{\tau} \ell^+ \ell^-$ ($\ell = e$ or $\mu$), using a 562 $\rm fb^{-1}$\ data set. The branching fraction of $\tau^- \rightarrow \pi^- e^+ e^- \nu_\tau$ is measured to be $\mathbf{ \mathcal{B}(\tau^-\rightarrow \pi^- e^+ e^- \nu_\tau) = (2.11 \pm 0.19 \pm 0.30) \times 10^{-5}}$, where the first uncertainty is statistical and the second is systematic. An upper limit is set on the branching fraction of $\tau^- \rightarrow \pi^- \mu^+ \mu^- \nu_\tau$, $\mathbf{\mathcal{B}(\tau^-\rightarrow \pi^- \mu^+ \mu^- \nu_\tau) < 1.06 \times 10^{-5}}$, at 90\% confidence level.

  2 citations

• 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 | Toggle abstract · pdf

  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.

  4 citations