J. A. Garzón

Origin of the low-mass electron pair excess in light nucleus-nucleus collisions

Abstract We report measurements of electron pair production in elementary p + p and d + p reactions at 1.25 GeV / u with the HADES spectrometer. For the first time, the electron pairs were reconstructed for n + p reactions by detecting the proton spectator from the deuteron breakup. We find that the yield of electron pairs with invariant mass M e + e − > 0.15 GeV / c 2 is about an order of magnitude larger in n + p reactions as compared to p + p . A comparison to model calculations demonstrates that the production mechanism is not sufficiently described yet. The electron pair spectra measured in C + C reactions are compatible with a superposition of elementary n + p and p + p collisions, leaving little room for additional electron pair sources in such light collision systems.

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