Proton-helium elastic scattering from 45 to 400 GeV

Abstract

The elastic proton-helium differential cross section has been determined for incident laboratory energies from 45 to 400 GeV in the range $0.003\ensuremath{\le}|t|\ensuremath{\le}0.52$ (${\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^{2}$ by means of the internal-gas-jet-target technique. The differential cross section drops 4-5 orders of magnitude to the first dip at $|t|\ensuremath{\simeq}0.22$ (${\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^{2}$. The shrinkage in the slope of the differential cross section is found to be twice as fast as that in the proton-proton case. The slope parameter at $|t|\ensuremath{\simeq}0$ is described by the formula $b=24+1.13\mathrm{ln}s$, where $b$ is in (${\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^{\ensuremath{-}2}$ and $s$ is in ${\mathrm{GeV}}^{2}$. The elastic proton-helium cross section is normalized to the known elastic proton-proton cross section using data taken with a helium and hydrogen mixture as a target. The proton-helium total cross section is determined from the optical theorem. The total cross section rises by 4% between 100 and 400 GeV. Results are presented on the real part of the elastic-scattering amplitude and on the total elastic cross section. The experimental differential cross sections are compared to Glauber-model predictions.