Semileptonic decays of $B_c$ meson to S-wave charmonium states in the perturbative QCD approach

Abstract

Inspired by the recent measurement of the ratio of $B_c$ branching fractions to $J/\psi {\pi }^{+}$ and $J/\psi {\mu }^{+}{\nu }_{\mu }$ final states at the LHCb detector, we study the semileptonic decays of $B_c$ meson to the S-wave ground and radially excited 2S and 3S charmonium states with the perturbative QCD approach. After evaluating the form factors for the transitions $B_c\to P,V$, where $P$ and $V$ denote pseudoscalar and vector S-wave charmonia, respectively, we calculate the branching ratios for all these semileptonic decays. The theoretical uncertainty of hadronic input parameters are reduced by utilizing the light-cone wave function for $B_c$ meson. It is found that the predicted branching ratios range from $10^{-6}$ up to $10^{-2}$ and could be measured by the future LHCb experiment. Our prediction for the ratio of branching fractions $\frac{\mathcal{B}\mathcal{R}(B_c^{+}\to J/\Psi {\pi }^{+})}{\mathcal{B}\mathcal{R}(B_c^{+}\to J/\Psi {\mu }^{+}{\nu }_{\mu })}$ is in good agreement with the data. For $B_c\to Vl{\nu }_l$ decays, the relative contributions of the longitudinal and transverse polarization are discussed in different momentum transfer squared regions. These predictions will be tested on the ongoing and forthcoming experiments.

Comments: 12 pages, 3 figures, 5 tables