The polarization of protons emitted in $\left(p,2p\right)$ reactions has been measured for three kinds of targets at $1\text{GeV}$. The values of the polarization that we obtain are significantly smaller than the values predicted using the nucleon-nucleon (NN) interaction in free space, and the discrepancy between the two is seen to increase monotonically as a function of the effective mean density, which is defined as a measure of the sensitivity of a reaction to density-dependent terms of the interaction. The experimental data are also compared with a model calculation that includes a relativistic effect, and it is found that inclusion of this effect is able to account for about half of the density-dependent discrepancy between the experimental results and the values predicted with the free space NN interaction. These results, in conjunction with the previous results at $392\text{MeV}$, indicate that this discrepancy is not caused by a contribution of multistep processes and provide further evidence that there exists a medium effect.

• Received 14 February 2003

DOI:https://doi.org/10.1103/PhysRevC.69.024604