Scattering of 19.2 GeV/cProtons on Free Protons in Nuclear Emulsion

An experimental study has been made of the elastic scattering of protons by free protons at a laboratory momentum of 19.2 GeV/c. The proton beam was directed at perpendicular incidence into water-loaded nuclear emulsions which were used as both target and detector. For elastic $p-p$ scattering the total cross section was found to be 9.4±1.3 mb. At zero angle the measured value of the differential cross section was higher than that predicted by the optical theorem, indicating the existence of a real part of the forward scattering amplitude or a spin dependence of the total proton-proton cross section. An analysis of other experimental data above 2.5 GeV is presented confirming the above result and is compared with the predictions of a Regge-Pole model at zero angle.