The ${\rm Y}(nS)\to B_{(c)}$ transition form factors and their applications to semileptonic and nonleptonic weak decays

Abstract

The semileptonic and nonleptonic decays of the ${\rm Y}(nS)$ with $n=1,2,3,4$ are investigated within the covariant light-front quark model (CLFQM). Using the form factors of the transitions ${\rm Y}(nS)\to B_{(c)}$ obtained from the CLFQM, we calculate the branching ratios of the decays ${\rm Y}(nS)\to B_{(c)}\ell {\nu }_{\ell }$ and ${\rm Y}(nS)\to B_{(c)}M$ with $\ell =e,\mu ,\tau$ and $M$ referring to $\pi (\rho ),K^{(\ast )},D^{(\ast )},D_s^{(\ast )}$. One can find that the branching ratios of the decays ${\rm Y}(3S)\to B_c\ell {\nu }_{\ell }$ are the largest among those of considered semileptonic decays and can amount to $10^{-9}$; As to the nonleptonic decays, ${\rm Y}(3S)\to B_c\rho$ and ${\rm Y}(3S)\to B_c{D}_s^{(\ast )}$ have the largest branching ratios, which reach up to $10^{-10}$. Given the identification and detection efficiency of final states, searching for these weak decay modes should be fairly challenging in future experiments. The forward-backward asymmetry $A_{FB}$ and the longitudinal polarization fraction $f_L$ are also calculated for those semileptonic decays.

25 pages, 4 figures