Measurements of the antiproton-proton elastic cross section in the beam momentum range between 180 and 600 MeV/c

The differential cross section for antiproton-proton elastic scattering has been measured for the beam momenta between 180 and 600 MeV/c. The real-to-imaginary ratio of the forward elastic scattering amplitude is derived from the Coulomb-nuclear interference. The ratio is found to be close to zero between 180 and 500 MeV/c with a minimum of ρ=-0.14 at 260 MeV/c. This result is contrary to model predictions. The phase shifts for the s-, p- and d-waves are extracted. The partial wave compositions of the elastic and inelastic cross sections have been determined. A large contribution of the p-wave is identified in the antiproton-proton interactions at small momenta.