Charge form factors and nucleon shape

TL;DR

This paper decomposes the proton charge form factor into symmetric and quadrupole parts, linking neutron charge form factor to nucleon shape and interpreting scattering data as evidence of a nonspherical quark-antiquark distribution.

Contribution

It introduces a novel decomposition of the proton charge form factor, connecting it to the nucleon's intrinsic quadrupole moment and shape, using quark model relations.

Findings

Neutron charge form factor reflects an intrinsic quadrupole component.

Proton shape is inferred as nonspherical based on form factor analysis.

Recent scattering data interpreted as evidence of nonspherical quark-antiquark distribution.

Abstract

To obtain further information on the geometric shape of the nucleon, the proton charge form factor is decomposed into two terms, which are connected respectively with a spherically symmetric and an intrinsic quadrupole part of the proton's charge density. Quark model relations are employed to derive expressions for both terms. In particular, the proton's intrinsic quadrupole form factor is obtained from a relation between the N -> Delta and neutron charge form factors. The proposed decomposition shows that the neutron charge form factor is an observable manifestation of an intrinsic quadrupole form factor of the nucleon. Furthermore, it affords an interpretation of recent electron-nucleon scattering data in terms of a nonspherical distribution of quark-antiquark pairs in the nucleon.