Charge Densities of the Neutron and Proton

A model-independent analysis of the infinite-momentum-frame charge density of partons in the transverse plane is presented for the nucleon. We find that the neutron-parton charge density is negative at the center, so that the square of the transverse charge radius is positive, in contrast with many expectations. Additionally, the proton’s central $d$ quark charge density is larger than that of the $u$ quark by about 30%. The proton (neutron) charge density has a long range positively (negatively) charged component.

Figure 1

Upper panel: proton charge density $\rho (b)$. Lower panel: neutron charge density. The solid curves use the parameterization of 17, and the dashed (red) curve uses 16.

Figure 2

Upper panel: $F_1$. Lower panel: $b\rho (b)$ in transverse position space. The solid curves are obtained using 17 and the dashed curves with 16.

Figure 3

Transverse densities for up $u$ (solid line) and down $d$ (dashed line) quarks. Each is normalized to unity.