The Bc → ψ(2S)π, ηc(2S)π decays in the perturbative QCD approach

Nonleptonic two-body B-c decays including radially excited psi(2S) or eta(c)(2S) mesons in the final state are studied using the perturbative QCD approach based on k(T) factorization. The charmonium distribution amplitudes are extracted from the n = 2, l = 0 Schrodinger states for the harmonic oscillator potential. Utilizing these distribution amplitudes, we calculate the numerical results of the B-c -> psi(2S), eta(c)(2S) transition form factors and branching fractions of B-c -> psi(2S)pi, eta(c)(2S)pi decays. The ratio between two decay modes B-c -> psi(2S)pi and B-c -> J/psi pi is compatible with the experimental data within uncertainties, which indicates that the harmonic-oscillator wave functions for psi(2S) and eta(c)(2S) work well. It is found that the branching fraction of B-c -> eta(c)(2S)pi, which is dominated by the twist-3 charmonium distribution amplitude, can reach the order of 10(-3). We hope it can be measured soon in the LHCb experiment.