HadronPhysics Departmentin the Past Overview

Strangeness and electromagnetic radiation from strongly interacting systems (hadrons and nuclei) - these are the research topics of the hadron department.

To gain with these probes new insights in properties of hadrons and nuclear matter in collisions we participate in several experimental collaborations. At GSI/Darmstadt the detector systems KaoS and FOPI offer the possibility to study properties of hadrons produced in heavy-ion collisions. The kaon and anti-kaon production near or below the threshold have been measured with the magnet spectrometer KaoS. An abnormal enhancement of anti-kaon production in heavy-ion collisions at equivalent beam energies has been detected. Preliminary interpretations of this effect point to an anti-kaon mass reduction (sometimes interpretated as indication of partial restoration of chiral symmetry in dense nuclear matter). Very recent measurements at KaoS focus on kaon and anti-kaon detection in reactions with various beam and target combinations to get a systematic mass dependence. Last year a series of experiments with a proton beam has been performed.

With the 4p detectorFOPI also hidden strangeness is measurable, e.g., in f production which is identified via the kaon-anti-kaon decay channel. Presently the kaon spectra and K^-/K⁺ ratios, at midrapidity are analyzed; the results corroborate the pedicted in-medium modification of K^- masses. Evidences for azimuthal anisotropies in kaon squeeze-out are found.

The mentioned detector systems are multi-purpose installations. Therefore, a much wider set of various interesting aspects has been explored and reported in a series of publications.

Complementary to the mentioned measurements of hadron spectra in heavy-ion collisions one needs a detailed knowledge on hadron reactions in the same energy region. The cooler synchrotron COSY/Jülich provides a suitable device to study hadron-induced reactions at hadrons or nuclei. Essential components of the time of flight (TOF) detector installation have been built up in Rossendorf. The first series of measurements with COSY-TOF are devoted to the strangeness production in the reaction pp->pLK+ and to bremsstrahlung in the reaction pp->ppg. In addition, in close collaboration with the Technical University Dresden the reaction pp->pnp⁺ has been measured by using the one-layered barrel.

ANKE is an internal spectrometer in the COSY ring. The decisive wire chamber are constructed in Rossendorf. Among the first experiments is the exploration of kaon and anti-kaon production at light nuclei; the concept of this experiment has been mainly elaborated by scientists from our institute.

To ensure a participation in future developments, the third drift chamber plane for the HADES experiment at GSI are built up in Rossendorf. It is the aim of this experiment to seek for a direct verification of the hypothesis that properties of hadrons are modified in a nuclear environment, i. e.HADES is devoted to in-medium hadron spectroscopy.

The theory group in the hadron physics department is accompanying these experimental activities. Predictions and interpretations of selected topics in the realm of strange and rare electromagnetic probes are provided. Some of these calculations refer to the energy range as covered by the experiments performed with FZD participation, others deal with varions aspects of the quark-gluon plasma accessible only at higher beam energies.