The role of the qqqq(q)over-bar components in the electromagnetic transition γ*N → N* (1535)

The helicity amplitudes A(1/2)(p) and S-1/2(p) for the electromagnetic transition gamma*N -> N* (1535) are calculated in the quark model that is extended to include the lowest-lying qqqq (q) over bar 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(1/2)(p) decreases at the photon point, Q(2) = 0 to the empirical range. The qqqq (q) over bar components contain s (s) over bar pairs, which is consistent with the substantial width for N eta decay of the N* (1535). The best description of the momentum dependence of the empirical helicity amplitudes is obtained by assuming that the qqqq (q) over bar 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(1/2)(p) and S-1/2(p) although with significant improvement.