HADES: H igh A cceptance D i- E lectron S pectrometer at GSI:

1. Theory: QCD sum rules Strangeness in the Nuclear Medium Clean Probes for High Densities: HADES Theory: Transport model calculations count rate Highly Compressed Baryonic Matter: CBM Rare Hadronic Probes Program: Structure of Matter • Hadronic processes on femto-meter scales: essential for early phases of generation of matter in the universe (big bang). • These processes govern the behavior of nuclear matter compressed by gravitation: e.g. neutron stars before possible collapse into black hole. • Strange probes (L, K±) are well suited to study these processes in the laboratory  series of experiments (Kaon spectrometer,GSI, Darmstadt, equipped in part by IKH) completed in 2005. Decisive contribution by IKH. • Access properties of L, K± inside hadronic matter. • HADES: High Acceptance Di-Electron Spectrometer at GSI: • European collaboration of 10 countries. • explore in-medium properties of light vector mesons in hadronic matter with excellent mass resolution and hight acceptance. • Tool: electromagnetic decay of ρ, ω, Φ mesons in the nuclear medium • Weak final state interaction  di-lepton decay channels are ideal direct probes to study in-medium modifications of mesons, i.e. self-energies, decay widths, and fundamental electromagnetic properties. The nucleus as laboratory. g, p,p or nuclei beams produce e.g. a ρ-meson via a pion in hadronic matter. Inside this matter the ρ-meson decays via ρ → γ* → e+e-. The electron-positron pair carries an imprint of the information on the former ρ-meson. Rings of glowing gas of super-nova 1987 A. Multi-Cyle processes may cook heavy nuclei out of light nuclei, concentrating mass. • Data may answer how K- mesons may balance positively charged hadrons at high nuclear matter densities  alternative scenario, to pure neutron matter inside neutron stars. • Most recent results: • Hypernuclear bound states in small, cold nuclei (PRL 93 (2004) 242501) • Extract self-energy of K± mesons in hadronic from data on proton-nucleus collisions: sizeable modification of K- properties at normal nuclear matter density (PRL (2006) in print) • K± production in nucleus-nucleus collisions reaching 2-3 times normal nuclear matter density (PRL 95 (2005) 012301) Tests of a multiwire drift chamber at the detector workshop of FZR/IKH (upper panel). Inside a chamber 13 layers with ~ 7000 wires positioned with a precision of ± 20 mm, position resolution of ± 100 mm. Signals are read out by TDC chips, drift gas helium isobutane mixture. The operational voltage of the chambers is up to 2000 V. The FZR built six chambers (right: mounting of one of the chambers into its position at the spectrometer). Modifications of the properties of particles like r and other mesons have been proposed by various theories. These studies are complementary to experiments with L, K±. Such modifications of light vector mesons can also shed light on questions of the origin of mass in the universe. A precise determination of the self-energies of mesons with HADES helps to understand the hierarchy of masses on all scales of physics, a major topic of contemporary physics. Two examples indicating the modification of K± self-energies in differential observables. Collisions of Au+Au (left) exhibit a distinctive flow pattern for K+ (upper) and K- (lower) figure. Calculations not taking into account modified self-energies (dashed curves) fail to explain the data. This also holds for p+Au and p+C collisions (middle and right) First result from HADES: measured distribution (solid circles) of invariant mass mee of electron-positron pairs for C+C collisions at 2 AGeV. The various colored histograms display simulations of the expected contributions of r mesons as well as other sources (denoted by p, D, h, w). The sum of these contributions (red) is considerably lower than the data at medium invariant masses (200-700 MeV/c2). (figure from R. Holzmann et al (HADES Collaboration) in Nucl. Phys. A (2006). • From experiments on the omega meson in nuclear matter an in-medium change of 4-quark condensates can be deduced (PRL 95 (2005) 232301) and the behavior of rho meson is determined • FAIR research facility launched at GSI, Darmstadt in 2003 by German BMBF. • CBM (Compressed Baryon Matter) experiment investigates nucleus-nucleus collisions at the highest densities and rates yet achieved in the laboratory, approaching the critical end point of the phase diagram of nuclear matter. • HADES will be integrated into the new detector system, bridging current and future studies. • IKH contribution: Theoretical support, R&D of new state-of-the-art detector techniques, e.g. straw tubes, high resolution timing devices, like resistive plate counters (RPC). RPC are tested and may be used at FZR‘s ELBE. • Description of HADES data require: • collisional broadening • medium modified spectral functions • of rho and omega mesons • sizeable eta Dalitz and bremsstrahlung • contributions; the latter one calculable from • diagrams like Time resolution (76 ps s) of RPC prototype referenced against the ELBE radio frequency. 34 MeV electrons were scattered off a thin aluminum foil and detected under 45°. An even better time resolution is expected for optimized detectors. Supported by: Bundesministerium für Forschung und Technologie, BMBF Deutscher Akademischer Austauschdienst Gesellschaft für Schwerionenforschung, Darmstadt, GSI EU 6th framework, I3HP Forschungszentrum Jülich, FZJ INTAS-GSI