Extended van Royen–Weisskopf formalism for lepton–antilepton meson decay widths within nonrelativistic quark models

Abstract

The classical van Royen–Weisskopf formula for the decay width of a meson into a lepton–antilepton pair is modified in order to include nonzero quark momentum contributions within the meson as well as relativistic effects. Besides, a phenomenological electromagnetic density for quarks is introduced. The meson wave functions are obtained from two different models: a chiral constituent quark model and a quark potential model including instanton effects. The modified van Royen–Weisskopf formula is found to improve systematically the results for the widths, giving an overall good description of all known decays.