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

TL;DR

This study measures proton polarization transfer in helium-4 to investigate how nucleon properties are altered within the nuclear medium, providing high-precision data that support density-dependent modifications of nucleon form factors.

Contribution

It provides the first high-precision measurements of polarization transfer in 4He(e,e'p)3H at specific Q^2 values, testing models of medium modifications and final-state interactions.

Findings

Data agree with relativistic models including medium modifications.

Alternative models with charge-exchange interactions also describe the data.

Results constrain theoretical descriptions of nucleon behavior in nuclei.

Abstract

Polarization transfer in quasi-elastic nucleon knockout is sensitive to the properties of the nucleon in the nuclear medium. In 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. The measured polarization-transfer coefficients transverse and longitudinal to the momentum-transfer direction are well described by a fully relativistic calculation when a density-dependent medium modification of the nucleon form factors is included in the model. Results of an alternative model show that the ratio of these observables is also well described through strong charge-exchange final-state interactions. The induced polarization in the (e,e'p) reaction is sensitive to the final-state interactions and the data from E03-104 will further constrain these models.