Antiproton-Nucleon Cross Sections from 0.5 to 1.0 BeV

Abstract

Antiproton-production and nucleon-interaction cross sections were investigated for antiprotons in the energy range 0.5 to 1.0 BeV. The antiprotons were distinguished from other particles produced at the Bevatron by a system of scintillation and velocity-selecting-\ifmmode \check{C}\else \v{C}\fi{}erenkov counters. The excitation function and momentum distribution were recorded for antiproton production in carbon and compared with statistical model expectations.The antiprotons were directed by a system of bending and focusing magnets to a liquid hydrogen target. An array of plastic scintillation counters, which almost completely surrounded the hydrogen target, was used to determine the $\overline{p}\ensuremath{-}p$ total, elastic, inelastic, and charge-exchange cross sections. Near 500 MeV the total $\overline{p}\ensuremath{-}p$ cross section is about 120 mb, and it slowly decreases to 100 mb near 1 BeV. The inelastic cross section, which is principally due to the annihilation process, represents nearly $\frac{2}{3}$ of the total cross section. The elastic-scattering distribution is highly peaked in the forward direction and can be fitted by an optical model.The total and partial cross sections were also determined for the collisions of antiprotons with deuterons. The $\overline{p}\ensuremath{-}d$ total and inelastic cross sections were found to be approximately 1.8 times the $\overline{p}\ensuremath{-}p$ cross sections. Corrections were made for the shielding of nucleons within the deuteron in order to ascertain the $\overline{p}\ensuremath{-}n$ interaction. The results indicate that the $\overline{p}\ensuremath{-}p$ and $\overline{p}\ensuremath{-}n$ cross sections are very nearly equal in this energy region, and that they satisfy the inequalities required by charge independence.