Study of the in-medium nucleon electromagnetic form factors using a light-front nucleon wave function combined with the quark-meson coupling model

Abstract We study the nucleon electromagnetic (EM) form factors in symmetric nuclear matter as well as in vacuum within a light-front approach using the in-medium inputs calculated by the quark-meson coupling model. The same in-medium quark properties are used as those used for the study of in-medium pion properties. The zero of the proton EM form factor ratio in vacuum, the electric to magnetic form factor ratio μ p G E p ( Q 2 ) / G M p ( Q 2 ) ( Q 2 = − q 2 > 0 with q being the four-momentum transfer), is determined including the latest experimental data by implementing a hard constituent quark component in the nucleon wave function. A reasonable fit is achieved for the ratio μ p G E p ( Q 2 ) / G M p ( Q 2 ) in vacuum, and we predict that the Q 0 2 value to cross the zero of the ratio to be about 15 GeV 2 . In addition the double ratio data of the proton EM form factors in 4 He and H nuclei, [ G E p 4 He ( Q 2 ) / G 4 He M p ( Q 2 ) ] / [ G E p 1 H ( Q 2 ) / G M p 1 H ( Q 2 ) ] , extracted by the polarized ( e → , e ′ p → ) scattering experiment on 4 He at JLab, are well described. We also predict that the Q 0 2 value satisfying μ p G E p ( Q 0 2 ) / G M p ( Q 0 2 ) = 0 in symmetric nuclear matter, shifts to a smaller value as increasing nuclear matter density, which reflects the facts that the faster falloff of G E p ( Q 2 ) as increasing Q 2 and the increase of the proton mean-square charge radius. Furthermore, we calculate the neutron EM form factor double ratio in symmetric nuclear matter for 0.1 Q 2 1.0 GeV 2 . The result shows that the neutron double ratio is enhanced relative to that in vacuum, while for the proton it is quenched, and agrees with an existing theoretical prediction.