Hyperon Production in Proton-Nucleus Collisions at 42 GeV Center of Mass Energy
The subject of this thesis is a measurement of hyperon production ratios which is of special interest as a reference on Quark Gluon Plasma search. The data used in this analysis have been taken with a minimum bias trigger at the fixed target experiment HERA-B, which uses the 920 GeV proton beam of the HERA storage ring at DESY. $\Lambda$, $\Xi$ and $\Omega$ hyperons produced in collisions using carbon and tungsten wires as targets were reconstructed. Hyperon ratios are presented for the rapidity range $-1.5 < y < 0.5$ (where they where measured), extrapolated to the whole phase space and to $y = 0$. The main results at $y = 0$ are $\frac{\overline{\Lambda}}{\Lambda} = 0.88 \pm 0.07$ (error including systematic error) and $\frac{\overline{\Xi}}{\Xi} = 0.69 \pm 0.12$ (statistical uncertainty only) for the carbon target. These values are compared to proton--nucleus and nucleus--nucleus data above and below HERA-B energies and are comparable with both. In the rapidity range $-1.5 < y < 0.5$ the ratio $\frac{\overline{\Lambda}}{\Lambda}$ is significantly different for the two target materials, whereas extrapolated to the whole phase space it is not. A possible explanation in terms of multiple scatterings in the nucleus is given. The distribution of the $\Lambda$ particle--anti-particle asymmetry versus Feynman's scaling variable $x_f$ using the carbon target is found to be in good agreement with measurements from pion--nucleus reactions at 500 GeV $\pi$-beam energy.
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