Exclusive semileptonic $B_c$-meson decays to radially excited charmonium and charm meson states

TL;DR

This paper calculates form factors and branching ratios for semileptonic $B_c$-meson decays to excited charmonium and charm states using the relativistic independent quark model, providing predictions testable at current colliders.

Contribution

It introduces a comprehensive calculation of form factors and decay observables for excited state decays within the RIQ model, including lepton mass effects and lepton flavor universality tests.

Findings

Predicted branching fractions are within experimental detection range.

Results agree with other models and can be tested at LHC and Tevatron.

Predicted observables suggest possible new physics beyond the Standard Model.

Abstract

In the wake of recent measurements of ratios of semileptonic branching fractions: ${\cal R}_{J/\psi}, {\cal R}_D$ and ${\cal R}_{D^*}$ reported by the LHCb, BELLE and HFLAV Collaborations, we calculate invariant form factors for the exclusive semileptonic $B_c$-meson decays to radially excited charmonium and charm meson states in the full kinematical region within the framework of relativistic independent quark (RIQ)model. We evaluate the lepton mass effect in the decay processes induced by $b\to c,u$ transition at the quark level. Our predictions on branching fractions for $B_c\to \eta_c/\psi(nS)$ are found $\sim10^{-2}-10^{-4}$ and that for $B_c\to D^*(nS)$ are $\sim 10^{-4}$ in their $e^-$ decay modes, which lie within the detection accuracy of current experiment. Our predictions on branching fractions, forward backward asymmetry and asymmetry parameter are found in reasonable agreement with other model predictions; which can hopefully be tested in future experiments at LHC and Tevatron. Our predicted observable ${\cal R}$ in this sector are found comparable to other standard model (SM) predictions that violate the lepton flavor universality hinting at new physics beyond SM.