Measurement of and with a semileptonic tagging method
arXiv preprint arXiv:1910.05864, 2019•arxiv.org
The experimental results on the ratios of branching fractions $\mathcal {R}(D)={\cal B}(\bar
{B}\to D\tau^-\bar {\nu} _ {\tau})/{\cal B}(\bar {B}\to D\ell^-\bar {\nu} _ {\ell}) $ and $\mathcal
{R}(D^*)={\cal B}(\bar {B}\to D^*\tau^-\bar {\nu} _ {\tau})/{\cal B}(\bar {B}\to D^*\ell^-\bar {\nu} _
{\ell}) $, where $\ell $ denotes an electron or a muon, show a long-standing discrepancy with
the Standard Model predictions, and might hint to a violation of lepton flavor universality. We
report a new simultaneous measurement of $\mathcal {R}(D) $ and $\mathcal {R}(D^*) …
{B}\to D\tau^-\bar {\nu} _ {\tau})/{\cal B}(\bar {B}\to D\ell^-\bar {\nu} _ {\ell}) $ and $\mathcal
{R}(D^*)={\cal B}(\bar {B}\to D^*\tau^-\bar {\nu} _ {\tau})/{\cal B}(\bar {B}\to D^*\ell^-\bar {\nu} _
{\ell}) $, where $\ell $ denotes an electron or a muon, show a long-standing discrepancy with
the Standard Model predictions, and might hint to a violation of lepton flavor universality. We
report a new simultaneous measurement of $\mathcal {R}(D) $ and $\mathcal {R}(D^*) …
The experimental results on the ratios of branching fractions and $\mathcal{R}(D^*) = {\cal B}(\bar{B} \to D^* \tau^- \bar{\nu}_{\tau})/{\cal B}(\bar{B} \to D^* \ell^- \bar{\nu}_{\ell})$, where denotes an electron or a muon, show a long-standing discrepancy with the Standard Model predictions, and might hint to a violation of lepton flavor universality. We report a new simultaneous measurement of and , based on a data sample containing events recorded at the resonance with the Belle detector at the KEKB collider. In this analysis the tag-side meson is reconstructed in a semileptonic decay mode and the signal-side is reconstructed in a purely leptonic decay. The measured values are and , where the first uncertainties are statistical and the second are systematic. These results are in agreement with the Standard Model predictions within , and standard deviations for , and their combination, respectively. This work constitutes the most precise measurements of and performed to date as well as the first result for based on a semileptonic tagging method.
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