Prof. Dr. Harald Appelshäuser

Institut für Kernphysik
Goethe- Universität
Max-von-Laue-Str.1 60438 Frankfurt am Main

Telefon: ++49 (0) 69 798-47034 oder 47023

Research Interest

Nucleus–nucleus collisions at high energyA new state of matter is created when atomic nuclei are heated and compressed to a few times the ground state density. In this state, the constituents of nucleons – quarks and gluons – behave like a soup of quasi-free particles. The formation of this so-called Quark-Gluon Plasma (QGP) is one of the exciting consequences of asymptotic freedom of QCD, the theory of strong interactions. We believe that our universe has formed a transient QGP state a few microseconds after the Big Bang, before it froze out to the hadronic matter we observe today. In modern experiments at particle accelerators, we try to create the QGP and study its properties. In the year 2000, the experimental groups at CERN-SPS claimed evidence for QGP formation in high-energy nucleus – nucleus collisions. This observation was further supported by detailed studies at the RHIC accelerator in Brookhaven (Long Island, USA).    

Experiments with participation of the working group

CERES The CERES experiment at CERN-SPS is devoted to the measurement of electron-positron pairs emerging from high energy nucleus-nucleus collisions. Anomalous production of e+e- pairs may stem from thermal radiation and therefore indicate the formation of a thermalized QGP. Furthermore, e+e- pairs are sensitive to the properties of hadrons in the hot and dense medium. The observed e+e- anomaly may be related to a fundamental aspect of QGP formation, the restoration of chiral symmetry. The experimental program at SPS has been finished, however, the analysis and physics interpretation of the existing data is still going on.

ALICE The ALICE experiment is presently under preparation. It will start operation in 2008 at the world’s largest particle accelerator, the LHC at CERN. The high collision energy (30 times more than at RHIC and 300 times more than at SPS) will produce a very hot and long-lived QGP. Furthermore, Pb-Pb collisions at LHC energies will give access to an entirely new kinematical regime. This allows to employ rare probes with sufficient rate which will facilitate a detailed study of the properties of QGP. The experimental conditions at LHC impose a serious challenge to the design and construction of the detectors. The ALICE group in Frankfurt is involved into the construction of the central barrel of ALICE, in particular the Time Projection Chamber (TPC) and the Transition Radiation Detector (TRD). In addition, fast and intelligent online data processing systems are needed to pick out interesting signals from a huge background of conventional events. For this purpose, a High Level Trigger (HLT) system for ALICE is being developed.

CBM CBM (Compressed Baryonic Matter) will be the dedicated heavy-ion experiment at the future FAIR (Facility for Antiproton and Ion Research) complex at GSI in Darmstadt, Germany. With CBM we will explore the QCD phase diagram in the region of moderate temperatures but very high baryon densities with A+A collisions of 10-45 AGeV beam energy. A key goal will be the search for the phase transition between hadronic and partonic matter and a possible critical endpoint of this transition. Moreover, CBM will aim for an understanding and the characterization of the high density baryonic matter created in these A+A collisions.

Further information:

Working Group
Helmholtz Research School        Publications