η\eta meson reconstruction in pp reactions at 2.2 GeV with HADES

The HADES spectrometer installed at GSI Darmstadt is devoted to study the production of di-electron pairs from proton, pion and nucleus induced reactions at 1-2 AGeV. In pp collisions at 2.2 GeV we have focused mainly on exclusive reconstruction of the $\eta$ meson decays in the hadronic ($\eta\to\pi^{+}\pi^{-}\pi^{0}$) and the electromagnetic channels ($\eta\to e^{+}e^{-}\gamma$). We present analysis techniques and discuss first results on $\eta$ production, with the main focus on comparisons of reconstructed distributions to results obtained by other experiments and theoretical predictions.Comment: Presented on Meson2006 conference, 4 pages, 4 figure

Dielectron Production in C+C Collisions at 1 GeV/u and the Solution to the DLS Puzzle

The production of e+e- pairs in C+C collisions at 1 GeV/u was investigated with the HADES experiment at GSI, Darmstadt. In the invariant-mass region $0.15\: GeV/c^{2} \leq M_{ee} \leq 0.5\: GeV/c^{2}$ the measured pair yield shows a strong excess above the contribution expected from hadron decays after freeze-out. The data are in good agreement with the results of the former DLS experiment for the same system and energy.Comment: 6 pages, 3 figures, conference proceedings: Quark Matter 2008, Jaipur (India), 4-10 February 2008, submitted to J. Phys. G: Nuclear and Particle Physic

Probing resonance matter with virtual photons

In the energy domain of 1-2 GeV per nucleon, HADES has measured rare penetrating probes (e+e-) in C+C, Ar+KCl, d+p, p+p and p+Nb collisions. For the first time the electron pairs were reconstructed from quasi-free n+p sub-reactions by detecting the proton spectator from the deuteron breakup. An experimentally constrained NN reference spectrum was established. Our results demonstrate that the gross features of di-electron spectra in C+C collisions can be explained as a superposition of independent NN collisions. On the other hand, a direct comparison of the NN reference spectrum with the e+e- invariant mass distribution measured in the heavier system Ar+KCl at 1.76 GeV/u shows an excess yield above the reference, which we attribute to radiation from resonance matter. Moreover, the combined measurement of di-electrons and strangeness in Ar+KCl collisions has provided further intriguing results which are also discussed.Comment: 10 pages, 3 figures, proceedings of the International Nuclear Physics Conference - INPC 2010, Vancouver, Canada, July 4 - 9 201

In-medium effects on K-0 mesons in relativistic heavy-ion collisions

We present the transverse momentum spectra and rapidity distributions of pi(-) and K-S(0) in Ar + KCl reactions at a beam kinetic energy of 1.756 A GeV measured with the High Acceptance Di-Electron Spectrometer (HADES). The reconstructed K-S(0) sample is characterized by good event statistics for a wide range in momentum and rapidity. We compare the experimental pi(-) and K-S(0) distributions to predictions by the Isospin Quantum Molecular Dynamics (IQMD) model. The model calculations show that K-S(0) at low transverse momenta constitute a particularly well-suited tool to investigate the kaon in-medium potential. Our K-S(0) data suggest a strong repulsive in-medium K-0 potential of about 40 MeV strength.We gratefully acknowledge the useful discussions with J. Aichelin and H. Oeschler. The HADES collaboration gratefully acknowledges the support by BMBF grants 06TM970I, 06GI146I, 06FY171, and 06DR135 (Germany), by GSI (TMFR1, GI/ME3, OF/STR), by Excellence Cluster of Universe (Germany), by grants GA AS CR IAA100480803 and MSMT LC 07050 (Czech Republic), by grant KBN 5P03B 140 20 (Poland), by INFN (Italy), by CNRS/IN2P3 (France), by grants MCYT FPA2000-2041-C02-02 and XUGA PGID T02PXIC20605PN (Spain), by grant UCY-10.3.11.12 (Cyprus), by INTAS grant 06-1000012-8861 and EU contract RII3-CT-2004-506078.Peer reviewe

Study of hadron properties in cold nuclear matter with HADES

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