Study of Nuclear Medium Effects by Recoil Polarization up to High Momentum Transfers

section associated with the occurrence of color transparency, in the context of the parton model and PQCD have been proposed. Experimental evidence of color transparency can also be inferred from (e,e'p) reactions at high momentum transfers by studying the A and Q 2 dependence of the nuclear absorption of the knocked out proton. Color transparency is expected to lead to a modification of the final state interaction (FSI) of the struck nucleon with respect to the prediction of the conventional picture in which the nucleons are assumed to be structureless. Frankfurt, Strikman and Zhalov 3 have examined the possibility to observe color transparency by studying the Q 2 behavior of the (e,e'p) reaction cross sections to specific final hole states in the residual (A-1) nucleus. This proposal also plans to measure the normal component of the recoil polarization of the ejected proton, Pn. In the absence of any nuclear medium effects, Pn is independent of the polarization of the beam and should be zero to first order in PWIA due to time reversal symmetry. Hence this effect can be used to great advantage as an effective filter in the study of FSI in nuclei and also to observe the onset of color transparency in nuclei at high momentum transfers. We therefore plan to study nuclear medium effects by measuring the Q 2 variation of the cross sections and the normal component of the recoil polarization, Pn in the (e,e' r p) reaction on deuterium ( 2 H) and other nuclei ( 4 He, 12 C, and 16 O) at essentially the same kinematics for each nucleus in the Q 2 range of 1 to 6 (GeV/c) 2 with the pair of high resolution spectrometers in Hall A. The reaction would also be performed on the proton, where Pn = 0 at all momentum transfers due to absence of FSI.