Measurement of polarization-transfer to bound protons in carbon and its virtuality dependence

TL;DR

This study measures polarization transfer to bound protons in carbon, revealing deviations from free-proton behavior that depend on proton virtuality but not on local nuclear density, indicating a universal pattern.

Contribution

It provides the first detailed measurement of polarization transfer ratios in carbon, highlighting a universal virtuality dependence independent of local nuclear density.

Findings

Deviations from unity in polarization ratios for bound protons

Dependence of the ratio on proton virtuality

No observed dependence on local nuclear density

Abstract

We measured the ratio $P_{x}/P_{z}$ of the transverse to longitudinal components of polarization transferred from electrons to bound protons in $^{12}\mathrm{C}$ by the $^{12}\mathrm{C}(\vec{e},e'\vec{p})$ process at the Mainz Microtron (MAMI). We observed consistent deviations from unity of this ratio normalized to the free-proton ratio, $(P_{x}/P_{z})_{^{12}\mathrm{C}}/(P_{x}/P_{z})_{^{1}\mathrm{H}}$, for both $s$- and $p$-shell knocked out protons, even though they are embedded in averaged local densities that differ by about a factor of two. The dependence of the double ratio on proton virtuality is similar to the one for knocked out protons from $^{2}\mathrm{H}$ and $^{4}\mathrm{He}$, suggesting a universal behavior. It further implies no dependence on average local nuclear density.