Measurement of Pion Transparency in Nuclei

Abstract

We propose to measure pion electroproduction off {sup 1}H, {sup 2}, {sup 12}C, {sup 64}Cu, and {sup 197}Au, and extract the pion transparency through the nuclear medium between Q{sup 2} = 1 and 5 (GeV/c){sup 2}. The pion transparency is predicted to be a signature of the onset of nuclear filtering and/or Color Transparency. Recent experiments have reported evidence for Color Transparency effects at Q{sup 2} approx 10 (GeV/c){sup 2}. The occurrence of nuclear filtering could potentially explain the apparent discrepancy between (proton) nuclear transparencies found in quasielastic A(e,e'p) and A(p,2p) experiments. The occurrence of these effects is an effective signature of the approach to the factorization regime in meson electroproduction experiments, necessary for the access to Generalized Parton Distributions. Measurable effects of approx. 40% are predicted for this region of Q{sup 2}. The proposed experiment seeks to measure the pion transparency with 5-10% uncertainties, dominated by systematics, up to Q{sup 2} = 5 (GeV/c){sup 2}.