Semileptonic decays Bc→(ηc,J/Ψ)lv in the perturbative QCD approach

In this paper we study the semileptonic decays of B_c^-→(η_c,J/Ψ)l^-v_l. We first evaluate the B_c→(η_c,J/Ψ) transition form factors F₀(q²), F₊(q²), V(q²) and A_0,1,2(q²) by employing the pQCD factorization approach, and then we calculate the branching ratios for all considered semileptonic decays. Based on the numerical results and the phenomenological analysis, we find that: (a) the pQCD predictions for the values of the B_c→η_c and B_c→J/Ψ transition form factors agree well with those obtained by using other methods; (b) the pQCD predictions for the branching ratios of the considered decays are Br(B_c^-→η_c e^-v_e(μ^-v_μ)=(4.41_-1.09^+1.22)×10^-3, Br(B_c^-→η_cτ^-v_τ) =(1.37_-0.34^+0.37)×10^-3, Br(B_c^-→J/Ψ e^-v_e(μ^-v_μ)) =(10.03_-1.18^+1.33)×10^-3, and Br(B_c^-→J/Ψτ^-v_τ) =(2.92_-0.34^+0.40)×10^-3; and (c) we also define and calculate two ratios of the branching ratios R_ηc and R_J/Ψ, which will be tested by LHCb and the forthcoming Super-B experiments.