First measurement of the polarisation transfer on the proton in the reactions e' p) and e' p)

The measurement of the polarisation transfer to the proton in the reactions H({, e' P) and D(~, e' P) per- formed with longitudinally polarised electrons in quasi-free kinematics is presented. The coincidence measurement was executed at Q2 ~ 8 fm -2 using the 855 MeV, c.w. beam of the Mainz Microtron MAMI. The recoil polarisation was determined by means of a carbon analyser. The experiment shows that the binding of the nucleon does not modify the polarisation P~ of the recoil proton within an error of Ap~/p~ ~ 10%. The measured polarisation agrees with recent theoretical predictions. Implications for the measure- ment of the electric form factor of the neutron using the D(~, e ~ ~) reaction are discussed. PACS" 13.40.Fn; 25.30.Bf