Eur. Phys. J. A (2009) 39: 195-204
https://doi.org/10.1140/epja/i2008-10698-x

Regular Article - Theoretical Physics

The role of the qqqq components in the electromagnetic transition N → N^*(1535)

¹ Institute of High Energy Physics, CAS, P.O. Box 918(4), 100049, Beijing, China
² Helsinki Institute of Physics, University of Helsinki, POB 64, 00014, Helsinki, Finland
³ Theoretical Physics Center for Science Facilities, CAS, P.O. Box 918(4), 100049, Beijing, China

Received: 16 October 2008
Revised: 27 November 2008
Accepted: 9 December 2008
Published online: 22 January 2009

Abstract

The helicity amplitudes A ^p _1/2 and S ^p _1/2 for the electromagnetic transition N → N ^*(1535) are calculated in the quark model that is extended to include the lowest-lying qqqq components in addition to the qqq component. It is found that with admixture of 5-quark components with a proportion of 20% in the nucleon and 25-65% in the N ^*(1535) -resonance the calculated helicity amplitude A ^p _1/2 decreases at the photon point, Q ² = 0 to the empirical range. The qqqq components contain s pairs, which is consistent with the substantial width for N decay of the N ^*(1535) . The best description of the momentum dependence of the empirical helicity amplitudes is obtained by assuming that the qqqq components are more compact than the qqq component. However, this version of the extended quark model still does not lead to a satisfactory simultaneous description of both A ^p _1/2 and S ^p _1/2 although with significant improvement.