Volume 340 - The 39th International Conference on High Energy Physics (ICHEP2018) - Parallel: Beyond the Standard Model
New results on R(D) and R(D*) from Belle
K. Matsuoka* On behalf of the BELLE Collaboration
*corresponding author
Full text: pdf
Published on: August 02, 2019
Abstract
Indications of lepton flavor universality violation in the decays $B \to D^{(*)}\tau\nu$ have triggered substantial interest and could be a hint for new physics. Useful observables to probe new physics in these decays are the ratios of the branching fractions, $R(D^{(*)}) \equiv \mathcal{B}(\bar{B} \to D^{(*)}\tau\bar{\nu}_{\tau})/\mathcal{B}(\bar{B} \to D^{(*)} \ell \bar{\nu}_{\ell})$, where $\ell = e$ or $\mu$, and the polarizations of the $\tau$ lepton and $D^*$ meson. This article summarizes analyses on those observables in the Belle experiment at the KEKB $e^+ e^-$ collider based on the full data set recorded by the Belle detector at the $\Upsilon(4S)$ resonance containing 772 million $B\bar{B}$ pairs. The analyses utilize different methods to reconstruct or tag the accompanying $B$ meson other than the $B$ of the semitauonic decay: semileptonic tagging for the simultaneous measurement of $R(D)$ and $R(D^*)$, and hadronic and inclusive ones for the measurement of the polarizations. In terms of the lepton flavor universality test, the ratio of the branching fractions of the purely leptonic decays, $\mathcal{B}(B^- \to \tau^- \bar{\nu}_{\tau})/\mathcal{B}(B^- \to \mu^- \bar{\nu}_{\mu})$, is also interesting because its theoretical uncertainty is small, though the $B^- \to \mu^- \bar{\nu}_{\mu}$ decay has not been discovered yet. Belle searched for this decay, and the result is also overviewed in this article.
DOI: https://doi.org/10.22323/1.340.0567
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