A phenomenological analysis of single pion photoproduction in the first resonance region

Single pion photoproduction in the first resonance region is investigated on the basis of noe-particle-exchange model. In addition to the Born terms, s-, t- and u-channel exchanges of N11, Δ33, N13, rho and ω are taken into consideration. In order to guarantee the unitarity we use the K-matrix method. The coupling constants and off-mass-shell parameters are determined by chi2-fit. The coupling constants obtained are constant with the values estimated by the use of the radiative decay widths and the results of low energy pion-nucleon or nucleon-nucleon analyses. Our predicted multipoles are in fairly good agreement with the experiments. Δ33 contribution is dominant to M sub(1+)sup((3/2)) and is very small to E sub(1+)sup((3/2)). The main contribution to E sub(1+)sup((3/2)) is due to the Born terms and the double zero observed in this multipole is well reproduced by incorporating unitarity. rho exchange is positively required to explain the absolute value and energy dependence of E sub(0+)sup((0)). It is difficult to reproduce the characteristic feature of sub(n) M sub(1-)sup((1/2)). It was argued that this structure will show the onset of N11 resonance. However, its contribution if too small to support this argument. (auth.)