Abstract
This article summarizes recent developments in B\to D^{(\ast)}\tau\nuB→D(*)τν decays. We explain how to extract the tau lepton’s production properties from the kinematics of its decay products. The focus is on hadronic tau decays, which are most sensitive to the tau polarizations. We present new results for effects of new physics in tau polarization observables and quantify the observation prospects at BELLE II.
Highlights
Semi-leptonic B meson decays with tau leptons are important probes of lepton universality in weak interactions
We have shown that the properties of the tau lepton in B → Dτν decays can be extracted from the tau’s decay products with a good sensitivity
BELLE II has the potential to achieve measurements of the longitudinal and perpendicular polarizations, as well as the tau forwardbackward asymmetry, in the standard model at the level of 10%. This prediction crucially relies on hadronic tau decays, which have the highest sensitivity to the tau properties
Summary
Semi-leptonic B meson decays with tau leptons are important probes of lepton universality in weak interactions. The detection of tau leptons is challenging, but recent progress at BELLE and LHCb shows that measurements beyond total decay rates are possible. This makes B → Dτν and B → D∗τν decays a key area of study at the new BELLE II experiment. Lepton and meson polarizations are interesting, because they are direct probes of the underlying interaction. Observables have a good potential to probe the underlying production process In addition to these developments, observed deviations in the branching ratios of B → D(∗)τν decays, widely referred to as the RD(∗) puzzle, have inspired searches for new particles with non-universal lepton interactions. Where q is the four-momentum of the tau-neutrino pair
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