Radiative decays of bottomonia into charmonia and light mesons

Abstract

In the framework of nonrelativistic QCD, we study the radiative decays of bottomonia into charmonia, including $Υ\to χ_{cJ}γ$, $Υ\to η_cγ$, $η_b\to J/ψγ$, and $χ_{bJ}\to J/ψγ$. We give predictions for their branching ratios with numerical calculations. E.g., we predict the branching ratio for $η_b\to J/ψγ$ is about $1\times 10^{-7}$. As a phenomenological model study, we further extend our calculation to the radiative decays of bottomonia into light mesons by assuming the $f_2(1270)$, $f_2'(1525)$ and other light mesons to be described by nonrelativistic $q\bar q ~(q=u,d,s)$ bound states with constituent quark masses. The calculated branching ratios for $Υ\to f_2(1270)γ$ and $Υ\to f_2'(1525)γ$ are roughly consistent with the CLEO data. Comparisons with radiative decays of charmonium into light mesons such as $J/ψ\to f_2(1270)γ$ are also given. In all calculations the QED contributions are taken into account and found to be significant in some processes.