Polarization effects in the elastic $e \vec p \to \vec e p$ and $\vec e \vec p \to e p$ processes in the case of parallel spins

TL;DR

This paper analyzes polarization effects in elastic electron-proton scattering with parallel spins, showing how polarization measurements can reveal deviations in form factor scaling and serve as tests for specific proton structure hypotheses.

Contribution

It provides a numerical analysis of polarization observables in elastic scattering, highlighting their sensitivity to form factor scaling violations and proposing new experimental approaches.

Findings

Longitudinal polarization of scattered electrons can differ by up to 70% depending on form factor scaling.

Double spin asymmetry is insensitive to form factor scaling violations, with differences not exceeding 2.32%.

Results suggest polarization experiments can test the scaling behavior of Sachs form factors.

Abstract

In the one-photon exchange approximation, we analyze polarization effects in the elastic $\vec e \vec p \to e p$ and $ e \vec p \to \vec e p$ processes in the case when the spin quantization axes of a target proton at rest and an incident or scattered electron are parallel. To do this, in the kinematics of the SANE Collaboration experiment, using the J. Kelly and I. Qattan parametrizations for the Sachs form factor ratio $R\equiv \mu_p G_E/G_M$, a numerical analysis was carried out of the dependence of the longitudinal polarization degree transferred to the scattered electron in the $e \vec p \to \vec e p$ process and double spin asymmetry in the $\vec e \vec p \to e p$ process on the square of the momentum transferred to the proton as well as on the scattering angle of the electron. It is established that the difference in the longitudinal polarization degree of the scattered electron in the $ e \vec p \to \vec e p$ process in the case of conservation and violation of the scaling of the Sachs form factors can reach 70 \%. This fact can be used to set up polarization experiments of a new type to measure the ratio $R$. For double spin asymmetry in the $\vec e \vec p \to e p$ process, the corresponding difference does not exceed 2.32 \%. This fact means that it's not sensitive to the effects of the Sachs form factor scaling violation and could be used as test for the $R\approx 1$ equality.