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The production of strange hadrons and electromagnetic radiation from colliding
hadron systems allows insights in the properties of dense nuclear matter as
formed in violent cosmic processes like super-novae and as present in a certain phase
of the big bang. In particular, the experimental research of the
department focuses on in-medium modifications of hadrons,
i. e. their behavior when embedded in strongly interacting matter. Various heavy-ion
experiments in the 1 GeV range point to such changes in a medium.
For instance, dedicated measurements by the KaoS and FOPI collaborations at the
heavy-ion synchrotron SIS in Darmstadt can be interpreted by a slight mass enhancement of
kaons and a significant mass reduction of anti-kaons. While these interesting findings can be
attributed to an evidence for partial restoration of chiral symmetry in dense nuclear matter
produced in the course of heavy-ion collisions, other interpretations are conceivable,
too.
In this respect the measurements of kaon production in proton-nucleus collisions represent
the missing link for systematically understanding strangeness production. During the last
years the COSY-11 and TOF collaborations at the cooler synchrotron COSY in Jülich
enlarged already the data basis for strangeness production in elementary hadron reactions.
Now the final analysis of the experiments by the KaoS collaboration at SIS and the ANKE
collaboration at COSY is eagerly waited for. Both experiments measure in complementary
phase space regions kaons produced by a proton beam at various energies impinging on
various target nuclei.
Hidden strangeness, e. g. in f mesons, represents another facet of strangeness degrees of
freedom. While f production is presently a hot topic in hadron reactions with respect to the
strangeness sea in nucleons and OZI rule violations, the f multiplicity in heavy-ion collisions
appears puzzling. The analysis of data taken previously with the FOPI detector points to a
f production probability being much larger than can be understood within the framework of
transport models.
While selected hadron channels, in particular these with strangeness, are sensitive to in-
medium effects, a direct measurement of spectral functions is desirable. This goal can be
accomplished, e. g., via the dielectron decay channels. Indeed, the starting HADES project
at SIS is aimed at studying the in-medium properties of r, w and f
mesons in a nuclear environment.
Since the fall of 2000, HADES is operating and begins with data taking while being completed.
The first multi-wire chamber built in our detector workshop has proven to work successfully.
The remaining 5 chambers from Rossendorf will be installed in the HADES detector system
during 2001 thus enabling, together with the other chambers, the required high-precision
resolution of charged particles tracks. HADES is expected to have a large scientific potential
for various investigations with the pion, proton and heavy-ion beams delivered at the SIS.
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. Most of these calculations refer to the energy range
covered by the experiments performed with FZR participation (see collaboration list below),
others deal with various phenomenological aspects of deconfined matter, as a state with
chiral symmetry restoration in the strongly interacting medium, produced in high-energy
heavy-ion reactions. Whereas the investigations of dense and hot hadronic matter as
produced in medium-energy collisions are of strong interest for the understanding of
astronomical objects like supernovae and neutron stars, the quark-gluon phase transition
studies are of relevance for more violent scenarios like the big bang.
Collaborations
ANKE:
Univ. Münster, FZ Jülich, Univ. Giessen, Univ. Bonn, Univ. Köln, Univ. Erlangen-
Nürnberg, Fachhochschule München, FZ Rossendorf, JINR Dubna (Russia), Univ. Tblisi
(Georgia), Petersburg Nuclear Physics Institute (Russia), ITEP Moscow (Russia), Russian
Academy of Science Moscow (Russia), ECN-Nuclear Energy (Netherlands), Jagellonian Univ.
Cracow (Poland), Moscow State University (Russia), Univ. College London (England), Soltan
Institute for Nuclear Studies (Poland),
spokesperson: K. Sistemich
FOPI:
Univ. Heidelberg, GSI Darmstadt, FZ Rossendorf, IPNE Bucharest (Romania), KFKI
Budapest (Hungary), LPC and Univ. Blaise Pascal Clermont (France), ITEP Moscow (Russia),
Kurchatov Institute Moscow (Russia), Korea Univ. Seoul (South Korea), IreS Strasbourg (France),
Univ. Warsaw (Poland), RBI Zagreb (Croatia),
spokesperson: N. Herrmann
HADES:
Univ. Frankfurt, TU München, Univ. Giessen, GSI Darmstadt, FZ Rossendorf,
Institute of Physics Bratislava (Slovakia), LNS Catania (Italy), LPC and Univ. Blaise Pascal
Clermont (France), Jagellonian Univ. Cracow (Poland), JINR Dubna (Russia), Univ. degli
Studi di Milano (Italy), ITEP Moscow (Russia), INR Moscow (Russia), MEPhI Moscow
(Russia), Univ. of Cyprus (Cyprus), Institute de Physique Nucleaire d'Orsay (France), Nuclear
Physics Institute Rez (Tschechia), Univ. of Santiago de Compostela (Spain), Univ. of Valencia
(Spain),
spokesperson: J. Friese
KaoS:
TU Darmstadt, Univ. Frankfurt, Univ. Marburg, GSI Darmstadt, Jagellonian Univ.
Cracow (Poland), FZ Rossendorf,
spokesperson: P. Senger
TOF:
Univ. Bochum, FZ Jülich, Univ. Bonn, TU Dresden, Fachhochschule Jülich, Univ.
Tübingen, Univ. Erlangen-Nürnberg, FZ Rossendorf, IUCF Bloomington (USA), INFN Torino
(Italy), SINS Warsaw (Poland),
local organizer: E. Roderburg
IKH
06/27/01
© B. Kämpfer
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