Measurement of transparency ratios for protons from short-range correlated pairs

TL;DR

This study measures the transparency ratios for protons from short-range correlated pairs in various nuclei, revealing lower transparency at high missing momentum and confirming surface dominance consistent with Glauber calculations.

Contribution

It introduces a novel observable, the transparency ratio for high-missing-momentum protons from 2N-SRC, and provides experimental data supporting surface scattering dominance.

Findings

Transparency ratios are 20-30% lower than low-momentum results.

Ratios scale as A^-1/3, indicating surface dominance.

Results agree with Glauber calculations and recent theoretical models.

Abstract

Nuclear transparency, Tp(A), is a measure of the average probability for a struck proton to escape the nucleus without significant re-interaction. Previously, nuclear transparencies were extructed for quasi-elastic A(e,e'p) knockout of protons with momentum below the Fermi momentum, where the spectral functions are well known. In this paper we extract a novel observable, the transparency ratio, Tp(A)/T_p(12C), for knockout of high-missing-momentum protons from the breakup of short range correlated pairs (2N-SRC) in Al, Fe and Pb nuclei relative to C. The ratios were measured at momentum transfer Q^2 > 1.5 (GeV/c)^2 and x_B > 1.2 where the reaction is expected to be dominated by electron scattering from 2N-SRC. The transparency ratios of the knocked-out protons coming from 2N-SRC breakup are 20 - 30% lower than those of previous results for low missing momentum. They agree with Glauber calculations and agree with renormalization of the previously published transparencies as proposed by recent theoretical investigations. The new transparencies scale as A^-1/3, which is consistent with dominance of scattering from nucleons at the nuclear surface.