Experimental study of the $A$($e$,${e}^{\ensuremath{'}}{\ensuremath{\pi}}^{+}$) reaction on $^{1}\mathrm{H}$, $^{2}\mathrm{H}$, $^{12}\mathrm{C}$, $^{27}\mathrm{Al}$, $^{63}\mathrm{Cu}$, and $^{197}\mathrm{Au}$

Experimental study of the $A$ ( $e$ , $e^{'} π^{+}$ ) reaction on ${}^{1}H$ , ${}^{2}H$ , ${}^{12}C$ , ${}^{27}{Al}$ , ${}^{63}{Cu}$ , and ${}^{197}{Au}$

X. Qian et al.

Phys. Rev. C 81, 055209 – Published 25 May 2010

Abstract

Cross sections for the ${}^{1}H$ ( $e, e^{'} π^{+}) n$ process on ${}^{1}H$ , ${}^{2}H$ , ${}^{12}C$ , ${}^{27}{Al}$ , ${}^{63}{Cu}$ , and ${}^{197}{Au}$ targets were measured at the Thomas Jefferson National Accelerator Facility (Jefferson Lab) to extract nuclear transparencies. Data were taken from $Q^{2} = 1.1$ –4.7 GeV $^{2}$ for a fixed center-of-mass energy of $W = 2.14$ GeV. The ratio of $σ_{L}$ and $σ_{T}$ was extracted from the measured cross sections for ${}^{1}H$ , ${}^{2}H$ , ${}^{12}C$ , and ${}^{63}{Cu}$ targets at $Q^{2} = 2.15$ and 4.0 GeV $^{2}$ , 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 $Q^{2}$ 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 ${}^{1}H$ ( $e, e^{'} π^{+}$ )n reaction from nuclear targets.