Proton-helium elastic scattering from 45 to 400 GeV

The elastic proton-helium differential cross section has been determined for incident laboratory energies from 45 to 400 GeV in the range $0.003\le \mathrm{}\left|t\right|\mathrm{}\le 0.52$ (${\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$ by means of the internal-gas-jet-target technique. The differential cross section drops 4-5 orders of magnitude to the first dip at $\mathrm{}\left|t\right|\mathrm{}\simeq 0.22$ (${\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$. 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 $\mathrm{}\left|t\right|\mathrm{}\simeq 0$ is described by the formula $b=24+1.13\mathrm{}\ln s$, where $b$ is in (${\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^{-2\mathrm{}}$ 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.