Measurement of the $pi$$sup -$p elastic scattering cross section near 180$sup 0$ between 600 and 1280 MeV/c

Differential cross sections for ${\ensuremath{\pi}}^{\ensuremath{-}}p$ elastic scattering over the angular range 155\ifmmode^\circ\else\textdegree\fi{} to 177\ifmmode^\circ\else\textdegree\fi{} in the center-of-mass system have been measured at 33 incident pion momenta in the range 600 to 1280 MeV/c. The experiment, which was performed at the Bevatron at the Lawrence Berkeley Laboratory, employed a liquid hydrogen target, a double-arm spectrometer, and standard counter techniques to detect the elastic events. The data from this experiment are compared to all other published data in this momentum region. The over-all agreement is good. The data of this experiment are also compared with the results of the recent phase-shift analysis by Almehed and Lovelace. In the momentum region between 700 and 900 MeV/c, the slope of the backward angular distribution goes rapidly through zero from negative to positive, and the magnitude of the differential cross section falls by more than a factor of 10. Momentum-dependent structure is seen in the extrapolated differential cross sections at 180\ifmmode^\circ\else\textdegree\fi{}. Two prominent dips in the 180\ifmmode^\circ\else\textdegree\fi{} differential cross sections appear at 880 and 1150 MeV/c. This structure is discussed in terms of a direct-channel resonance model that assumes only resonant partial waves are contributing to the cross sections for large scattering angles.