Quark interchange and deuteron electromagnetic form factors at large transfers

Abstract

The elastic electromagnetic form factors of the proton, neutron and deuteron at momentum transfers Q 2 ⩽ 10 ( GeV c ) 2 are discussed in the parton light-cone approach. The framework is an adaptation of the constituent interchange model to exclusive processes based on the factorization of the hadronic binding mechanisms described in terms of wave functions from the reaction mechanisms described by simple interchange of constituents. The constituent description for the deuteron is examined at two levels: the conventional level where one resolves the proton-neutron compositeness and the quark level where one resolves the quark compositeness of the nucleon constituents. Associated with the first level are the impulse approximation form factors which we describe in the nucleon parton approach. The light-cone description of the deuteron-neutron-proton (dnp) vertex is examined from a dynamical standpoint, the main emphasis being however on a phenomenological construction of wave functions. Predictions using such constructs are presented. The discussion of deuteron form factors at the quark level bears on the quark interchange mechanism between quarks in different nucleons. To prepare for this discussion we examine the core parton model of the nucleon based on a simplified two-particle representation in terms of an active quark correlated to a passive core. The initial version of the core model is considerably enhanced by an account of the spin-isospin structure and of the normalization. The predictions for the nucleon form factors and structure functions are used to test the model and gauge its various parameters. We then proceed without parameter adjustment to a discussion of the quark interchange deuteron form factors. The calculations are performed in a simplified factorization approximation for the dnp vertex. The quark interchange mechanism stands out as a serious competitor to the impulse approximation matching better the shape of the Q 2 dependence at large Q 2.