Analyzing the semileptonic and nonleptonic Bc → J/ψ, ηc decays

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Abstract This study focuses on the decay of the B c meson to S-wave charmonia. Starting with lattice inputs on B c → J/ψ form factors, we have obtained the B c → η c form factors using heavy quark spin symmetry (HQSS) relations between the associated form factors after parametrizing and extracting the possible symmetry breaking corrections. Using the q 2 shapes of these form factors, we have computed the branching fractions $$ \mathcal{B} $$ B ( $$ {B}_c^{-} $$ B c − → η c ℓ − $$ \overline{\nu} $$ ν ¯ ) (with ℓ = τ, μ(e)) and the decay rate distributions and have predicted the Standard model estimate for the observable R(η c ) = Γ( $$ {B}_c^{-} $$ B c − → η c τ − $$ \overline{\nu} $$ ν ¯ )/Γ( $$ {B}_c^{-} $$ B c − → η c μ − $$ \overline{\nu} $$ ν ¯ ) = 0.310 ± 0.042. In addition, we have estimated the radial wave functions $$ {\psi}_{B_c}^R $$ ψ B c R (0), $$ {\psi}_{J/\psi}^R $$ ψ J / ψ R (0) and $$ {\psi}_{\eta_c}^R $$ ψ η c R (0) at small Bc J/ψ ηc quark-antiquark distances from the available information on the form factors from lattice, the lattice inputs on the decay constants f J/ψ , $$ {f}_{\eta_c} $$ f η c , $$ {f}_{B_c} $$ f B c and experimental data on radiative and rare decays of the J/ψ and η c mesons. To do so, we choose the theory framework of non-relativistic QCD (NRQCD) effective theory. Using our results, we have predicted the branching fractions of a few non-leptonic decays of B c → J/ψ or η c and other light mesons. We have also updated the numerical estimates of the cross sections σ(e + e − → J/ψη c , η c γ) and predicted the branching fractions of Z boson decays to either J/ψ or η c final states or both.