Electric and Magnetic Form Factors of Proton in Relativistic Constituent Quark Model

Abstract

Based on relativistic constituent quark (RCQ) model, the electric and magnetic form factors are analyzed. The ratio of the two form factors for the proton , which is an image of its charge and magnetization distributions, is calculated in the light-front formulism of RCQ model. Recently, this ratio was measured at the Thomas Jefferson National Accelerator Facility (JLab) using the polarization technique. The new data presented span the range and are well described by a linear Q2 fit. Also, the ratio reaches a constant value while Q2 becomes larger than 2 (GeV)2. Our calculation results are presented and appear to be consistent with the experimental ones.

Contribution of Quark Structure Term in Nucleon Electric and Magnetic Form Factors

“…[1] In our previous paper we have calculated the nucleon form factors assuming pointlike quarks. [2] The calculation results of form factor G n E sharply differ from the experimental data. A possible way to solve such a discrepancy is to assume a non-trivial electromagnetic e.m. structure for extended CQ's.…”

“…As is known (Ref. [2]), the light front wave functions of hadrons are eigenvectors of a mass operator, e.g. M = M 0 + V , and of the non-interacting angular momentum operators j 2 and j n , where the vector n = (0, 0, 1) defines the spin quantization axis.…”

“…where the curly braces { } mean a list of indices corresponding to i = 1, 2, 3; ν i (τ i ) is the third component of the quark spin (isospin); + = 3 j=1 R + j ( k j⊥ , ξ j , m j ) with R + j ( k j⊥ , ξ j , m j ) being the usual generalized Melosh rotation. [2] In what follows we will limit ourselves to the case of a pure SU(6) symmetric canonical wave function, namely…”

“…where S 12 (T 12 ) is the total spin (isospin) of the quark pair (1,2). The normalization of the wave function ( 7) is…”

“…1 (2) have been estimated through a standard minimization procedure, where the experimental form factors of both nucleon and pion in a wide range of momentum transfer, up to high energy as the proton Q 2 30 (GeV/c) 2 , have been considered. This wide range is inspired by the fact that the onset of the perturbative QCD is not definitively localized.…”