Beyond the soft photon approximation in radiative production and decay of charged vector mesons

We study the effects of model-dependent contributions and the electric quadrupole moment of vector mesons in the decays V − → PP 0γ and τ → νV γ. Their interference with the amplitude originating from the radiation due to electric charges vanishes for photons emitted collinearly to the charged particle in the final state. This brings further support to our claim in previous works, that measurements of the photon energy spectrum for nearly collinear photons in those decays are suitable for a first measurement of the magnetic dipole moment of charged vector mesons. PACS 13.40-f, 14.40.Cs, 13.35.Dx In some recent papers [1, 2, 3], we have studied the possibility to obtain information about the experimental value of the magnetic dipole moment (MDM) of light charged vector mesons. We have focused our interest on the angular and energy distribution of photons emitted during the radiative decay [1] or production [2] processes of vector mesons. In Ref. [3] we have extended our analysis to include the finite width effects of these unstable particles. Just to illustrate the interest of the problem, let us emphasize that none of the magnetic dipole moments of resonances, neither elementary (as the W gauge boson) nor hadronic particles, have been measured yet. The only exception is the ∆ resonance, where the determinations of the MDM spread over a wide range [4]: 3.5 < μ∆++ < 7.5 in units of nuclear magnetons. This particular case makes inconclusive any comparison with theoretical predictions based on quark models [5]. Therefore, observables that could provide