G. Agakishiev

Dielectron production in Ar+KCl collisions at 1.76A GeV

We present results on dielectron production in 40 Ar+KCl collisions at 1.76A GeV. For the first time ω mesons could be reconstructed in a heavy-ion reaction at a bombarding energy which is well below the production threshold in free nucleon-nucleon collisions. The ω multiplicity has been extracted and compared to the yields of other particles, in particular of the φ meson. At intermediate e + e invariant masses, we find a strong enhancement of the pair yield over a reference spectrum from elementary nucleon-nucleon reactions suggesting the onset of non-trivial effects of the nuclear medium. Transverse-mass spectra and angular distributions have been reconstructed in three invariant mass bins. In the former unexpectedly large slopes are found for high-mass pairs. The latter, in particular the helicity-angle distributions, are largely consistent with expectations for ]

Partial wave analysis of the reaction p(3.5 GeV)+p → pK+Λ to search for the “ppK−” bound state

Employing the Bonn-Gatchina partial wave analysis framework (PWA), we have analyzed HADES data of the reaction p(3.5GeV ) + p !pK + �. This reaction might contain information about the kaonic cluster ”ppK − ” via its decay into p�. Due to interference effects in our coherent description of the data, a hypothetical KNN (or, specifically ”ppK − ”) cluster signal must not necessarily show up as a pronounced feature (e.g. a peak) in an invariant mass spectra like p�. 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 KNN cluster. At a confidence level of CLs=95% such a cluster can not contribute more than 2-12% to the total cross section with a pK + � final state, which translates into a production cross-section between 0.7 µb and 4.2 µb, respectively. The

pK + Λ final state: Towards the extraction of the ppK − contribution

Abstract The reaction p ( @ 3.5 GeV ) + p → p + Λ + K + can be studied to search for the existence of kaonic bound states like p p K − leading to this final state. This effort has been motivated by the assumption that in p + p collisions the Λ ( 1405 ) resonance can act as a doorway to the formation of the kaonic bound states. The status of this analysis within the HADES Collaboration, with particular emphasis on the comparison to simulations, is shown in this work and the deviation method utilized by the DISTO Collaboration in a similar analysis is discussed. The outcome suggests the employment of a partial wave analysis do disentangle the different contributions to the measured p K + Λ final state.

Study of exclusive one-pion and one-eta production using hadron and dielectron channels in pp reactions at kinetic beam energies of 1.25 GeV and 2.2 GeV with HADES

Abstract.We present measurements of exclusive

Inclusive dielectron production in proton-proton collisions at 2.2 GeV beam energy

\ensuremath \pi^{+,0}

Medium effects in proton-induced

and

K^{0}

\eta

production at 3.5 GeV

production in pp reactions at 1.25GeV and 2.2GeV beam kinetic energy in hadron and dielectron channels. In the case of

Baryon resonance production and dielectron decays in proton-proton collisions at 3.5 GeV

\pi^{+}_{}

Associate K^0 production in p+p collisions at 3.5 GeV: The role of Delta(1232)++

and