Search for Proton Medium Modifications in the 4He(e,e'p)3H Reaction

TL;DR

This study measures proton polarization in helium-4 to investigate potential modifications of proton properties within the nuclear medium, providing high-precision data that challenge existing models and suggest medium effects or strong final-state interactions.

Contribution

The paper presents new high-precision polarization transfer data in helium-4 that tests models of proton medium modifications and final-state interactions.

Findings

Measured polarization-transfer ratios differ from relativistic calculations.

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

Induced polarization data align with relativistic calculations, suggesting limited 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.