Speaker
Description
In this contribution we will discuss the production of $\Sigma^0$ baryons in Ag+Ag collisions at 1.58 AGeV beam energy measured by HADES. Although, the High Acceptance DiElectron Spectrometer (HADES) at GSI was primarily designed to measure Di-Electrons, it also features a very rich program measuring hadronic probes in the region of moderate temperature and high-baryon density in the QCD phase diagram. Recently, the spectrometer was upgraded with a new RICH photon detector and an electromagnetic calorimeter. While the first allows for a strongly improved electron identification, the latter allows for photon measurements in HADES for the first time without involving the conversion process.
Those experimental upgrades allow for a clear reconstruction of the $\Sigma^0$ baryon in Ag+Ag collisions at 1.58 AGeV beam energy in the electromagnetic decay to Lambda and photon. This collision energy is right at threshold for Lambda production, however it's below for the Sigma0. In p+p collisions a rise of the $\Lambda/\Sigma^0$ ratio is measured, which, if also existent for A+A collisions, would have strong impact on the extraction of ($T,\mu_B$) values from thermal models as the $\Lambda/\Sigma^0$ is usually fixed following isospin symmetry. The analysis presented in this work allows for a $\Sigma^0$ signal with a significance of roughly 10 in the $\Lambda \gamma$ channel while no signal is observed in the $\Lambda e^{\pm}$ channel reconstructing conversion photons and, if existing, Dalitz decays. Full acceptance and efficiency studies allow for a fully corrected $\Sigma^0$ production yield, extracting a $(\Lambda+\Sigma^0)/\Sigma^0$ ratio. This value is compared to and used in thermal models applied to HADES data or GiBUU analyzing the influence of the NN threshold in Ag+Ag.
| Category | Experiment |
|---|---|
| Collaboration (if applicable) | HADES |
