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

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 ${}^{12}\mathrm{C}(\vec{e},e^{\prime }\vec{p})$ 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.