ON THE GAMMA-N-DELTA QUADRUPOLE COUPLING CONSTANT(S)

The extraction of the gamma N Delta transverse and longitudinal quadrupole transition form factors gE and gC from the interference measured in (ep, e'p' pi 0) at resonance is discussed. It is shown that the background mechanisms in the non-resonant channels are substantially depressed thus allowing the direct determination of gC and g E. The two quantities, which have to be equal at pseudo-threshold, vary for 0>k2>-0.6 (GeV/c)2 between 0 and -0.1 gM. The necessity of an explicit evaluation of dispersive effects coming from pionic contributions to confirm their four-momentum transfer dependence and their connection with the pseudo-threshold value is stressed.