A lattice study of electromagnetic decays of vector-mesons

We present a lattice study of electromagnetic decays of vector mesons V into pseudoscalar mesons P, relevant to radiative decays V --> P-gamma and conversion decays V --> Pl + l-. The form factor f(q)(q2), associated with the electromagnetic current of the quark q, has been computed using Wilson fermions in the quenched approximation. The computations have been performed by averaging the results over 15 gauge configurations, generated by the Metropolis algorithm, at beta = 6.0, on a 20 X 10(2) x 40 lattice. By extrapolating linearly the form factor to q2 = 0. We have obtained f(u)(0) = 2.2 +/- 0.3 GeV-1 for a massless quark and f(s)(0) = 1.8 +/- 0.2 GeV-1 for a strange quark, in remarkable agreement with the experimental values, f(u)(0) = 2.32 +/- 0.08 GeV-1 and f(s)(0) = 1.84 +/- 0.06 GeV-1. A larger value of f(u)(0) is obtained from the vector meson dominance model. We have also estimated the partial widths for the conversion decays using both a linear dependence on q2 of the form factor and the vector meson dominance predictions.