Structure and Excitation Mechanism of the N^* in Photoproduction γ+p→N^*

概要

論文の詳細を見る
The photoproduction of nucleon resonances γ+p→N^* is theoretically examined in the framework of the fundamental triplet model of hadrons. The partial width of the decays N^*→N+γ and of the Breit-Wigner formula for the processes γ+p→N^*→N+π are obtained in terms of the internal quantum numbers and the structure parameters of the N and N^*'s. The basic assumption is as follows: The nucleon and its resonance levels are well described by the non-relativistic bound state wave functions of three constituent particles. Both the nucleon and the (3,3) -resonance, N_<33^*> belong to the 56-dimensional representation of the SU_6, and are further characterized by the S-wave internal space wave function. The other resonances are regarded as the single particle excitation mode in which one of constituents is in a higher angular momentum state. The electromagnetic interaction is U-spin invariant and its exchange current effect is neglected. First it is shown that the selection rule for electric and magnetic multipoles to induce the process γ+N→N^* is completely fixed by the above assumption and an additional hypothetical relation L+S=J which may be called the Kycia-Riley relation, where L, S and J are the internal orbital, spin and total angular momentum, respectively. Both the electric and magnetic multipoles (E_<J-1/2> and M_<J+1/2>) contribute to the excitation of the N_<1,2J^*>'s with I=(1/2), while only the magnetic multipole transition (M_<J-1/2) is necessary for the excitation of the N_<3,2J^*>'s with I=(3/2), I being the isospin of the resonance levels. Consequently the N_<11^*> (1400) excitation would be much suppressed in agreement with experiment. The partial widths for various N^* excitations are numerically obtained. It is shown that the existing experimental data on the N_<33^*> and N_<13^*> are consistent with them if the spatial extension of the bound state is put nearly equal to the nucleon Compton wave length. It is also noted that only the partial width of the N_<33^*> photoexcitation is not sensitive to the core radius in the long photon wave-length approximation and in the SU_6 symmetric limit of the internal space wave function.
理論物理学刊行会の論文
1967-05-25

Structure and Excitation Mechanism of the N^* in Photoproduction γ+p→N^*

スポンサーリンク

概要

著者

関連論文

スポンサーリンク