Polarization-transfer universality in quasi-elastic scattering

  David Izraeli  
Tel Aviv University
for the MAMI A1 Collaboration

In nuclei, the effects of the strong nuclear field on a bound nucleon are an interesting issue: do bound nucleons have the same properties as free ones?

Thus, measurements of the ratio of the polarization components of a proton which was knocked-out by a polarized electron (in quasi-free scattering) is a good tool to detect changes in the bound-proton structure, reflected in the ratio of the electric to magnetic form factors (FFs). The polarization transfer in the 2H(e,e'p) and 4He(e,e'p) reactions was measured, and observed deviations from calculation with free proton FFs were attributed to nuclear medium modifications. However, it is not clear what mainly affects these changes: is it the nuclear density, or is it due to the nucleon being off-shell in the nuclear medium.

In 12C the effective nuclear density for protons in s-shell is about twice as high as for p-shell protons. Polarization-transfer measurements by the reaction 12C(e,e'p), knocking out a proton from the s- or p-shell, can provide constraints on the in-medium FF ratio as a function of the local nuclear density. We performed a dedicated experiment at the Mainz Microtron (MAMI) measuring such effects. We present the analysis and the study of the nuclear density dependence of nuclear modifications, by comparing the 12C(e,e'p) results with those from the 2H(e,e'p) and 4He(e,e'p) reactions.