The position and the residues of the delta resonance pole in pion photoproduction

O. Hanstein, D. Drechsel, L. Tiator
1996 Physics Letters B  
We have analyzed the M_1+^(3/2) and E_1+^(3/2) multipole amplitudes of pion photoproduction in the framework of fixed-t dispersion relations. Applying the speed plot technique to our results for these multipoles, we have determined the position and the residues of the Δ (1232) resonance pole. The pole is found at total c.m. energy W = (1211 - 50i) MeV on the second Riemann sheet, and the ratio of the electric and magnetic residues is R_Δ = - 0.035 - 0.046 i, resulting in an E2/M1 ratio for the "dressed" delta resonance of - 3.5 %.
doi:10.1016/0370-2693(96)00855-6 fatcat:2y7hb3t6gvh4vhmx4bhyly2bge