Measurement of Nuclear Transparency for the A(e,e' pi^+) Reaction

TL;DR

This study measures how easily pions escape various nuclei during electron scattering, revealing deviations from traditional models and supporting the presence of color transparency effects predicted by quantum chromodynamics.

Contribution

First measurements of nuclear transparency for the A(e,e' pi^+) reaction across multiple nuclei and Q^2 values, providing evidence for color transparency phenomena.

Findings

Nuclear transparency varies with Q^2 and atomic number.

Results deviate from traditional nuclear physics expectations.

Data are consistent with color transparency predictions.

Abstract

We have measured the nuclear transparency of the A(e,e' pi^+) process in ^{2}H,^{12}C, ^{27}Al, ^{63}Cu and ^{197}Au targets. These measurements were performed at the Jefferson Laboratory over a four momentum transfer squared range Q^2 = 1.1 - 4.7 (GeV/c)^2. The nuclear transparency was extracted as the super-ratio of $(\sigma_A/\sigma_H)$ from data to a model of pion-electroproduction from nuclei without pi-N final state interactions. The Q^2 and atomic number dependence of the nuclear transparency both show deviations from traditional nuclear physics expectations, and are consistent with calculations that include the quantum chromodynamical phenomenon of color transparency.