Eur. Phys. J. A (2009) 42: 185-193
https://doi.org/10.1140/epja/i2009-10878-2

Regular Article - Theoretical Physics

Pion electro-production in the Roper region in chiral quark models

¹ Faculty of Education, University of Ljubljana and J. Stefan Institute, 1000, Ljubljana, Slovenia
² Faculty of Mathematics and Physics, University of Ljubljana and J. Stefan Institute, 1000, Ljubljana, Slovenia
³ Department of Physics and Centre for Computational Physics, University of Coimbra, 3004-516, Coimbra, Portugal

^* e-mail: bojan.golli@ijs.si

Received: 11 June 2009
Revised: 8 September 2009
Accepted: 17 September 2009
Published online: 3 October 2009

Abstract

We present a method to calculate pion electro-production amplitudes in a coupled-channel framework incorporating quasi-bound quark-model states. The method offers a clear prescription how to extract the resonant part of the amplitudes, even in the presence of different decay channels and a strong mixing of neighbouring resonances. The method is applied to the calculation of the M_1- and the S_1- amplitudes in the P11 partial wave in a simple chiral quark model. A good agreement with the observed M_1- amplitude is found with a significant contribution from the pion cloud. The same effect is also prominent in the S_1- amplitude but a rather uncertain data prevent us to draw a definitive conclusion.