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

Abstract

We study the exclusive semileptonic decays ${\rm Y}(1S)\to B_{(c)}\ell {\bar{\nu }}_{\ell }$, 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 $\mathcal{B}({\rm Y}(1S)\to B_{(c)}\ell {\bar{\nu }}_{\ell })$ 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 ${\rm Y}(1S)\to B_c\tau {\bar{\nu }}_{\tau }$. We show that the branching fraction of this decay can be enhanced by an order of magnitude using constraints from the $B\to D^{(\ast )}\ell {\bar{\nu }}_{\ell }$ and $B_c\to J/\psi \ell {\bar{\nu }}_{\ell }$ experimental data.

Comments: 18 pages, 4 figures, 5 tables, references added, to be published in Chinese Physics C