Speaker
Description
The measurement of $\Sigma$ hyperons is rather difficult because of their abundant decay into neutral particles.
For this reason, data are available only for few energy points in pp, pA and AA collisions, in particular, the energy gap between 2 and 4 GeV
remains unexplored. Also, since $\Sigma$ hypernuclei have not been measured so far, nothing is known quantitatively from experiments
about the $\Sigma$-N interaction. For these reasons precise measurements of $\Sigma$ hyperons are needed in the field of hadron physics.
We have studied the production of neutral $\Sigma^{0}$ baryons in the nuclear reaction p + Nb at an incident proton
energy $E_{kin}$ = 3.5 GeV. The measurement has been performed with the HADES experiment setup at GSI, Darmstadt.
From 4.2$\times$ 10$^{9}$ recorded events, $\Sigma^{0} \rightarrow \Lambda^{0} \gamma$ decays were identified via the
decay $\Lambda^{0} \rightarrow p \pi^{-}$ coincident with $e^{+}e^{-}$ pairs from external gamma conversion.
Experimental details, analysis procedures and background determination are presented. The momentum and the rapidity distribution
of the particle and an observed total of about 220 candidate events is used to pin down the $\Lambda$/$\Sigma$ ratio.
The obtained numbers and spectra are compared to predictions from transport model calculations and are discussed in the
context of thermal particle production in nuclear fireballs.
*supp. by BMBF(05P15WOFCA), GSI F$\&$E(5802045) and the Excellence Cluster Universe
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