Eur. Phys. J. A (2004) 19: 55-60
https://doi.org/10.1140/epjad/s2004-03-009-9

Hadronic resonances

Electroproduction of nucleon resonances

¹ Institut für Kernphysik, Johannes Gutenberg-Universität, D-55099 Mainz, Germany
² JINR Dubna, 141980 Moscow Region, Russia
³ Dipartimento di Fisica dell’Universita di Genova and I.N.F.N., Sezione di Genova, I-16164 Genova, Italy

Received: 30 October 2003
Published online: 12 February 2004

Abstract

The unitary isobar model MAID has been extended and used for a partial wave analysis of pion photo- and electroproduction in the resonance region W<2 GeV. Older data from the world data base and more recent experimental results from Mainz, Bates, Bonn and JLab for Q ² up to 4.0 (GeV/c)² have been analyzed and the Q ² dependence of the helicity amplitudes have been extracted for a series of four star resonances. We compare single-Q ² analyses with a superglobal fit in a new parametrization of Maid2003 together with predictions of the hypercentral constituent quark model. As a result we find that the helicity amplitudes and transition form factors of constituent quark models should be compared with the analysis of bare resonances, where the pion cloud contributions have been subtracted.