Eur. Phys. J. A (2021) 57: 228
https://doi.org/10.1140/epja/s10050-021-00546-0

Regular Article - Theoretical Physics

Proton and neutron form factors with quark orbital excitations

NRC “Kurchatov Institute” – ITEP, B. Cheremushkinskaya 25, 117259, Moscow, Russia

^a simonov@itep.ru

Received: 18 April 2021
Accepted: 29 June 2021
Published online: 10 July 2021

Abstract

Nucleon form factors play an especially important role in studying the dynamics of nucleons and explicit structure of the wave functions at arbitrary nucleon velocity. The purpose of the paper is to explain theoretically all four nucleon form factors measured experimentally in the cross section measurements (by the Rosenbluth method), yielding almost equal normalized form factors $G_E^p,G_M^p,G_M^n$), as well as in the polarization transfer experiments, where a strongly decreasing proton electric form factor has been discovered. It is shown, using relativistic hyperspherical formalism, that the nucleon wave functions in the lowest (hypercentral) approximation provide almost equal normalized form factors as seen in the Rosenbluth cross sections, but in the higher components they contain a large admixture of the quark orbital momenta, which strongly decreases $G_E^p$ and this effect is possibly detected in the polarization transfer method (not seen in the classical cross section experiments). Moreover, the same admixture of the higher components explains the small positive form factor $G_E^n$, which is zero in the hypercentral approximation. The resulting form factors, $G_M^p(Q),G_E^p(Q),G_M^n(Q)$ are calculated up to $Q^2\approx 10$ ${\text{GeV}}^2$, using the the Lorentz contracted nucleon wave functions and shown to be in reasonable agreement with experimental data.