Medium Modifications from 4He(e,e'p)3H

TL;DR

This study measures proton polarization in 4He(e,e'p)3H reactions at specific Q^2 values to investigate possible modifications of the proton form factor within the nuclear medium, providing data that challenge existing models.

Contribution

It provides high-precision polarization transfer data that suggest medium modifications of the proton form factor or strong final-state interactions, advancing understanding of nucleon behavior in nuclei.

Findings

Measured polarization-transfer ratios differ from relativistic calculations.

Data favor medium modifications of form factors or strong charge-exchange interactions.

Induced polarization data align with relativistic calculations, implying weaker final-state interactions.

Abstract

Polarization transfer in quasi-elastic nucleon knockout is sensitive to the properties of the nucleon in the nuclear medium, including possible modification of the nucleon form factor and/or spinor. In our recently completed experiment E03-104 at Jefferson Lab we measured the proton recoil polarization in the 4He(e,e'p)3H reaction at a Q^2 of 0.8 (GeV/c)^2 and 1.3 (GeV/c)^2 with unprecedented precision. These data complement earlier data between 0.4 and 2.6 (GeV/c)^2 from both Mainz and Jefferson Lab. The measured ratio of polarization-transfer coefficients differs from a fully relativistic calculation, favoring either the inclusion of a medium modification of the proton form factors predicted by a quark-meson coupling model or strong charge-exchange final-state interactions. The measured induced polarizations agree well with the fully relativistic calculation and indicate that these strong final-state interactions may not be applicable.