Study of the semileptonic decays $\Upsilon(1S)\to B_{(c)}\ell\bar{\nu}_\ell$

We study the exclusive semileptonic decays $\Upsilon(1S)\to B_{(c)}\ell\bar{\nu}_\ell$, where $\ell = e,\mu,\tau$. The relevant hadronic form factors are calculated using the Covariant Confined Quark Model developed previously by our group. We predict the branching fractions $\mathcal{B}(\Upsilon(1S)\to B_{(c)}\ell\bar{\nu}_\ell)$ to be of the order of $10^{-13}$ and $10^{-10}$ for the case of $B$ and $B_c$, respectively. Our predictions agree well with other theoretical calculations. We also consider the effects of possible New Physics in the case of $\Upsilon(1S)\to B_c\tau\bar{\nu}_\tau$. We show that the branching fraction of this decay can be enhanced by an order of magnitude using the constraints from the $B\to D^{(*)}\ell\bar{\nu}_\ell$ and $B_c\to J/\psi\ell \bar{\nu}_\ell$ experimental data.
Comment: 15 pages, 4 figures, 5 tables, submitted to Chinese Physics C