Polarization of Recoil Protons from Electron-Proton Scattering at 950 MeV

The recoil-proton polarization in elastic high-energy electron scattering on protons has been measured in order to check the validity of first Born approximation in this reaction. The transverse polarization is proportional to the imaginary part of the second order term (two-photon exchange term). 950-MeV electrons produced by the Orsay Linear Accelerator were scattered in a liquid-hydrogen target at about 90° c.m. The recoil protons were analyzed by a magnet system. Their polarization was then measured in a polarimeter constituted by a carbon scatterer and 4 spark chambers. The two transverse components of the polarization have been calculated by a method derived from maximum likelihood. The component perpendicular to the scattering plane was found to be 0.040±0.027. The transverse component in the scattering plane was found to be 0.000+0.028.