An independent quark model study of weak leptonic decays of pseudoscalar mesons

An independent quark model with a relativistic power-law potential is used to study the weak leptonic decays of light and heavy pseudoscalar mesons. The partial decay width and the decay constant for the weak leptonic decay are derived from the quark-antiquark momentum distribution amplitude which is obtained from the bound quark eigenfunction with the assumption of a strong correlation existing between quark-antiquark momenta inside the decaying meson in its rest frame. The model parameters are first determined from the application of the model to study the ground state hyperfine splitting of rho, K, D, D-s, B, B-s and B-c mesons. The same model with no adjustable parameters is then used to evaluate the decay constants f(M) and the decay widths of pseudoscalar mesons. The model predictions agree quite well with the available experimental data as well as with those of several other models. The decay constant for pion and kaon are obtained as f(pi) = 132 MeV and f(k) = 161 MeV which closely agree with experimental values. But in case of heavier mesons for which experimental data are not yet available, the present model gives its predictions as f(BC) > f(BS) > f(B), f(DS) > f(D), f(D) > f(B) and f(pi) > f(B) which are in conformity with most of other model predictions. The model predictions of the corresponding decay widths and the branching ratios for the (l (nu) over barl) and (tau(nu) over bar (tau)) decay modes are in close agreement with the available experimental data.