Measurement of the Proton-Antiproton Total Annihilation Cross Section at Low Energy

The $\overline{p}p$ total inelastic cross section has been measured in a hydrogen bubble chamber for $\overline{p}$ momenta from 100 to 550 MeV/c. Below 200 MeV/c the cross section increases rapidly to several barns. From this behavior it is inferred that high partial waves, perhaps to $L=3\mathrm{}$, are important in the annihilation at the lowest momenta studied. An abrupt change in the momentum dependence of the total absorption cross section occurs at about 350 MeV/c in the vicinity of previously observed structure in backward elastic scattering.