Experimental study of the A(e,e′π⁺) reaction on H1, H2, C12, Al27, Cu63, and Au197

Abstract

Cross sections for the H1(e,e′π+)n process on H1, H2, C12, Al27, Cu63, and Au197 targets were measured at the Thomas Jefferson National Accelerator Facility (Jefferson Lab) to extract nuclear transparencies. Data were taken from Q2=1.1-4.7 GeV2 for a fixed center-of-mass energy of W=2.14 GeV. The ratio of σL and σT was extracted from the measured cross sections for H1, H2, C12, and Cu63 targets at Q2=2.15 and 4.0 GeV2, allowing for additional studies of the reaction mechanism. In this article, we present the experimental setup and the analysis of the data in detail, including systematic uncertainty studies. Differential cross sections and nuclear transparencies as a function of the pion momentum at different values of Q2 are presented. Our results are consistent with the predicted early onset of color transparency in mesons. Global features of the data are discussed and the data are compared with model calculations for the H1(e,e′π+)n reaction from nuclear targets. © 2010 The American Physical Society.