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Employing the Bonn-Gatchina partial wave analysis framework (PWA), we have analyzed HADES data of the reaction p(3.5 GeV) + p → pK + Λ. This reaction might contain information about the kaonic cluster "pp K − " (with quantum numbers J P = 0 − and total isospin I = 1/2) via its decay into pΛ. Due to interference effects in our coherent description of the data, a hypothetical K N N (or, specifically "pp K − ") cluster signal need not necessarily show up as a pronounced feature (e.g. a peak) in an invariant mass spectrum like pΛ. Our PWA analysis includes a variety of resonant and non-resonant intermediate states and delivers a good description of our data (various angular distributions and two-hadron invariant mass spectra) without a contribution of a K N N cluster. At a confidence level of CL s = 95% such a cluster cannot contribute more than 2-12% to the total cross section with a pK + Λ final state, which translates into a production cross-section between 0.7 μb and 4.2 μb, respectively. The range of the upper limit depends on the assumed cluster mass, width and production process.

The centrality determination for Au + Au collisions at 1.23A GeV, as measured with HADES at the GSI-SIS18, is described. In order to extract collision geometry related quantities, such as the average impact parameter or number of participating nucleons, a Glauber Monte Carlo approach is employed. For the application of this model to collisions at this relatively low centre-of-mass energy of √ s NN = 2.42 GeV special investigations were performed. As a result a well defined procedure to determine centrality classes for ongoing analyses of heavy-ion data is established.

We present an analysis of the (1405) resonance produced in the reaction p + p → ± + π ∓ + K + + p at 3.5 GeV kinetic beam energy measured with the High Acceptance Dielectron Spectrometer (HADES) at the Gesellschaft für Schwerionenforschung (GSI). The two charged decay channels (1405) → ± π ∓ have been reconstructed for the first time in p + p collisions. The efficiency and acceptance-corrected spectral shapes show a peak position clearly below 1400 MeV/c 2 . We find a total production cross section of σ (1405) = 9.2 ± 0.9 ± 0.7 +3.3 −1.0 μb. The analysis of its polar angle distribution suggests that the (1405) is produced isotropically in the p − p center-of-mass system (CMS).