Dispersive analysis of omega/phi --> 3pi decays and the omega/phi --> pi0 gamma* transition form factors

Abstract

We present a dispersive analysis of the three-pion decays of the lightest isoscalar vector mesons. The framework allows for a consistent implementation of final-state interactions among all three pions, with the results being solely dependent on the pion-pion P-wave scattering phase shift. We compare our results with the very precise KLOE measurement of phi --> 3pi. The omega/phi --> 3pi partial-wave amplitude serves as input to a dispersive analysis of the omega/phi --> pi0 gamma* transition form factor. We compare to data for omega --> pi0 mu+ mu- by the NA60 collaboration and motivate an experimental measurement of the OZI forbidden phi --> pi0 l+ l- decays in order to understand the strong deviations in the omega channel.