A measurement of the polarization parameter in large angle proton-proton elastic scattering at 7.9 GeV/ c

The polarization parameter in proton-proton elastic scattering has been measured at an incident momentum of 7.9 GeV/ c and four-momentum transfers in the range 0.9 < | t| < 6.5 (GeV/ c) 2 using a high intensity unpolarized proton beam incident on a polarized proton target. The angle and momentum of the forward scattered protons were measured with a magnet spectrometer and scintillation counter hodoscopes and the angle of the recoil proton was measured using similar hodoscopes. A clean separation between the elastic scattering from free hydrogen and that coming from inelastic interactions and from interactions with complex nuclei in the target was obtained. The polarization shows substantial structure rising from zero at | t| = 1.0 (GeV/ c) 2 to a maximum at | t| = 1.7 (GeV/ c) 2 and then falling to zero at | t| = 2.0 (GeV/ c) 2. There is evidence of a further peak at | t| = 2.8 (GeV/ c) 2. Above | t| = 3.25 (GeV/ c) 2 the polarization is small and consistent with zero. A comparison of these data with data obtained at other beam momenta shows that the polarization parameter has a strong momentum dependence.