Proton-neutron structure-function difference in the resonance region

Abstract

A detailed analysis of the different structure functions vW 2 for deep-inelastic scattering off protons and neutrons is performed by means of the recent photoproduction phase-shift analysis of Moorhouse-Oberlack and a theoretical model for multipion production. The low-energy data taken as a function of ω W, are known to average the difference of the deep-inelastic structure functions, which in turn is related to the imaginary part of a I t = 1 forward Compton amplitude with one isovector and one isoscalar photon. The main results are: 1. (i) We establish by two independent calculations that the imaginary part of the I t = 1 Compton amplitude is entirely generated by resonances. 2. (ii) The I t = 1 imaginary part of the Compton amplitude is generated by only the resonant parts of the exclusive channels; the non-resonant multipoles do not contribute. Large real parts of the amplitudes in the exclusive channels, which are demanded by gauge invariance, cancel in the p-n difference. 3. (iii) We predict a positive contribution of the non-resonant incoherent 2 π production near threshold to the difference of the proton and neutron structure functions.