The NE11 experiment at SLAC and the neutron form factors

Abstract

The neutron electromagnetic form factors G{sub En} and G{sub Mn}, which reflect the charge and magnetization distributions within the neutron, are of fundamental importance for understanding nucleon structure, and are necessary for calculations of processes involving the electromagnetic interaction with complex nuclei. These quantities are functions of Q{sup 2}, the four-momentum transfer squared. SLAC experiment NE11 has measured these form factors out to a Q{sup 2} of 4.0 (GeV/c){sup 2} with high precision, and the results have been recently published. This paper provides some additional details on the extraction of G{sub Mn} and G{sub En} from the NE11 measurements. Several formalisms have been developed over the years which attempt to understand the nucleon form factors using basic physical principles. Vector Meson Dominance (VMD) models are based on superpositions of photon couplings to various vector mesons. These models generally involve free parameters which are fit to form factor data at low Q{sup 2}, and are not expected to be valid at high Q{sup 2}. For asymptotically large Q{sup 2}, dimensional scaling methods and perturbative Quantum Chromodynamics (pQCD) predict form factor behavior at large Q{sup 2}, but they do not make absolute magnitude predictions. To describe the form factor behavior at intermediate values of Q{sup 2}, a hybrid model by Gari and Kruempelmann (GK) uses VMD constraints at low Q{sub 2} and pQCD constraints at high Q{sup 2}. Free parameters in the model are adjusted to fit existing form factor data. Other approaches include the use of QCD sum rules to make absolute predictions, diquark models, and relativistic constituent quark models.