Proton propagation studied through the A dependence of the (e,e'p) reaction in the quasi-free region

Proton propagation has been studied using the (e,e'p) reaction in the quasifree region. The coincidence (e,e'p) cross section was measured at proton angles of 50.1 degree, 58.2 degree, 67.9 degree and 72.9 degree at a beam energy of 779.5 MeV and an electron angle of 50.4 degree for 12C, 27Al, 58Ni and 181Ta targets. The average proton energy was 175 MeV. The inclusive (e,e') cross sections were measured simultaneously. The ratio of the (e,e'p) yield to the (e,e') yield was compared to that calculated in the PWIA and an experimental transmission defined. Comparison of the experimental transmissions to those obtained from a classical calculation of the transmission, in which a density dependent nucleon-nucleon cross section incorporated the medium effects, yielded a proton mean free path in nuclear matter of 3.8 ± .25 fm. This is longer than the 2.4 fm obtained from the simple approximation λ = 1/ρσ using the free nucleon-nucleon cross section and including a correction for Pauli blocking. Global fits to the proton-nucleus elastic scattering data yields a mean free path of 7.1 fm for protons of energy 175 MeV, but gave results larger at the conjugate angle by 20-60% and smaller at 72.9 degree by 10-50%. The author concludes that the proton mean path in nuclear matter is less than that obtained from phenomenological optical model analyses but longer than that from λ = 1/ρσ corrected for Pauli Blocking