Wolfenstein parameters for s1/2 proton knockout (p,2p) reactions

A complete set of Wolfenstein parameters (Di'j), induced polarizations (P), and analyzing powers (Ay) have been measured for (p,2p) reactions on Li6, C12, and Ca40 targets in order to investigate possible nuclear medium effects on the nucleon-nucleon (NN) interaction. Most of these observables show significant reductions from the values for proton-proton scattering as monotonic functions of the nuclear density relevant to these reactions. The reductions of these Di'j are reasonably reproduced by nonrelativistic plane-wave and distorted-wave calculations based on the impulse approximation, demonstrating that these suppressions are attributed to changes of the two body kinematics due to the finite separation energies of these reactions, while the reductions of Ay and P are much more prominent than the calculations. The relativistic calculations, which partly explain the Ay and P reductions, cannot reproduce the Di'j data, but all the data are consistently reproduced when the parameters of the NN interaction in a meson exchange model are renormalized, suggesting possible modifications of the NN interaction by the surrounding nuclear medium.