Measurement of Pion Transparency in Nuclei

We propose to measure pion electroproduction off 1H, 2, 12C, 64Cu, and 197Au, and extract the pion transparency through the nuclear medium between Q2 = 1 and 5 (GeV/c)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 Q2 approx 10 (GeV/c)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 Q2. The proposed experiment seeks to measure the pion transparency with 5-10% uncertainties, dominated by systematics, up to Q2 = 5 (GeV/c)2