Measurement of the nuclear transparency in \textbf{A($e$,$e^\prime \pi^+$) reactions}$^1$

Color transparency is a phenomenon predicted by QCD in which hadrons produced at large $Q^2$ can pass through the nuclear medium with little or no interaction. Results will be presented from E01-107, an experiment that was successfully completed at Hall C at Jefferson Laboratory in 2004, where the pion electroproduction cross section from $Q^2 = 1.1~ \mathrm{to} ~4.8~ (\mathrm{GeV})^2$ was measured. The nuclear transparency is formed by the ratio of $(\sigma_A/\sigma_H)$ from the data and $(\sigma_A/\sigma_H)$ from a model of electroproduction from nuclei that does not include $\pi -N$ final state interactions. A signature of color transparency is the enhancement of the nuclear transparency at large $Q^2$ compared with predictions based on Glauber multiple scattering theory. An effect as large as $\approx 40\%$ due to color transparency is predicted in this $Q^2$ range by some models. This experiment will provide the first nuclear transparency data from ($e$,$e^\prime \pi^+$) reactions and seek unambiguous evidence for the existence of the color transparency effect. This work is supported by the US department of Energy under contract number DE-FC02-94ER40818 and DE-FG02-03ER41231 and Duke University. \newline $^{1}$On behalf of the Jefferson Laboratory E01-107 collaboration $^{2}$Laboratory for Nuclear Science, Massachusetts Institute of Technology, Cambridge, MA 02139, USA\\ $^{3}$Triangle Universities Nuclear Laboratory, Duke University, Durham, NC 277