Experimental study of the A(e,e 'pi(+)) [A (e, e prime pi superscript +)] reaction on H-1 [superscript 1 H], H-2 [superscript 2 H], C-12 [superscript 12 C], Al-27 [superscript 27 Al], Cu-63 [superscript 63 Cu], and Au-197 [superscript 197 Au]

摘要

Cross sections for the 1H(e,e′π+)n [superscript 1 H (e, e prime pi superscript +) n] process on 1H [superscript 1 H], 2H [superscript 2 H], 12C [superscript 12 C], 27Al [superscript 27 Al], 63Cu [superscript 63 Cu], and 197Au [superscript 197 Au] 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 [Q superscript 2 = 1.1-4.7] GeV2 [Ge V superscript 2] for a fixed center-of-mass energy of W=2.14 GeV. The ratio of σL [delta subscript L] and σT [delta subscript T] was extracted from the measured cross sections for 1H [superscript 1 H], 2H [superscript 2 H], 12C [superscript 12 C], and 63Cu [superscript 63 Cu] targets at Q2=2.15 [Q swuperscript 2 = 2.15] and 4.0 GeV2 [Ge V superscript 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 Q2 [Q superscript 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 1H(e,e′π+)n [superscript 1 H (e, e prime pi superscript +) n] reaction from nuclear targets.