Measurement of nuclear transparency for the A(e,e′π+) reaction

We have measured the nuclear transparency of the A(e,e′π+) process in H2, C12, Al27, Cu63, and Au197 targets. These measurements were performed at the Jefferson Laboratory over a four momentum transfer squared range Q2=1.1 to 4.7(GeV/c)2. The nuclear transparency was extracted as the super-ratio of (σA/σH) from data to a model of pion-electroproduction from nuclei without π-N final-state interactions. The Q2 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. © 2007 The American Physical Society.