Representation of results on γγ-formation of resonances by helicity amplitudes

It is suggested to use helicity amplitudes to represent the results of γγ-formation of resonances. There exists a one-to-one relation to the γγ partial width Γγγ which is obtained from the Breit-Wigner fit to the resonance cross section. The advantage of using the helicity amplitude is that the phase space and the spin factor are separated and the helicity amplitude is directly proportional to the matrixelement of the hadronic transition. (orig.)