T. Vasiliev

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.

First measurement of proton-induced low-momentum dielectron radiation off cold nuclear matter

Abstract We present data on dielectron emission in proton induced reactions on a Nb target at 3.5 GeV kinetic beam energy measured with HADES installed at GSI. The data represent the first high statistics measurement of proton-induced dielectron radiation from cold nuclear matter in a kinematic regime, where strong medium effects are expected. Combined with the good mass resolution of 2%, it is the first measurement sensitive to changes of the spectral functions of vector mesons, as predicted by models for hadrons at rest or small relative momenta. Comparing the e + e − invariant mass spectra to elementary pxa0+xa0p data, we observe for e + e − momenta P ee 0.8 GeV / c a strong modification of the shape of the spectrum, which we attribute to an additional ρ -like contribution and a decrease of ω yield. These opposite trends are tentatively interpreted as a strong coupling of the ρ meson to baryonic resonances and an absorption of the ω meson, which are two aspects of in-medium modification of vector mesons.

Medium effects in proton-induced

We present the analysis of the inclusive K 0 production in p + p and p + Nb collisions measured with the HADES detector (GSI Helmholtzzentrum for Heavy-Ion Research, Darmstadt) at a beam kinetic energy of 3.5 GeV. Data are compared to the Giessen Boltzmann-Uehling-Uhlenbeck (GiBUU) transport model. The data suggest the presence of a repulsive momentum-dependent kaon potential as predicted by the chiral perturbation theory (ChPT). For the kaon at rest and at normal nuclear density, the ChPT potential amounts to ≈ 35 MeV. A detailed tuning of the kaon production cross sections implemented in the model has been carried out to reproduce the experimental data measured in p + p collisions. The uncertainties in the parameters of the model were examined with respect to the sensitivity of the experimental results from p + Nb collisions to the in-medium kaon potential.

K^{0}

Abstract.We report on baryon resonance production and decay in proton-proton collisions at a kinetic energy of 3.5 GeV based on data measured with HADES. The exclusive channels

production at 3.5 GeV

pp rightarrow nppi^{+}

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

and

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

pprightarrow pppi^{0}

Lambda hyperon production and polarization in collisions of p(3.5 GeV)+Nb

as well as

Inclusive pion and η production in p+Nb collisions at 3.5 GeV beam energy

pprightarrow ppe^{+}e^{-}