Measurement of Angular Coefficients of $\bar{B}\to D^{\ast }\ell \bar{\hat{I}}{½}_{\ell }$: Implications for $|V_{cb}|$ and Tests of Lepton Flavor Universality

Abstract

We measure the complete set of angular coefficients $J_i$ for exclusive $\bar{B}\to D^{\ast }\ell \bar{\hat{I}}{½}_{\ell }$ decays ($\ell =e,\hat{I}¼$). Our analysis uses the full $711{\mathrm{fb}}^{-1}$ Belle data set with hadronic tag-side reconstruction. The results allow us to extract the form factors describing the $B\to D^{\ast }$ transition and the Cabibbo-Kobayashi-Maskawa matrix element $|V_{\mathrm{cb}}|$. Using recent lattice QCD calculations for the hadronic form factors, we find $|V_{\mathrm{cb}}|=(41.0\pm 0.7)\times 10^3$ using the BGL parameterization, compatible with determinations from inclusive semileptonic decays. We search for lepton flavor universality violation as a function of the hadronic recoil parameter $w$, and investigate the differences of the electron and muon angular distributions. We find no deviation from Standard Model expectations.