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First collision of heavy ions at the LHC in Geneva – LHC pre-accelerator was developed and built by GSI

The ALICE experiment, in which GSI is significantly involved, measures first nuclear reactions with record energies



Today, after almost one year of operating with relatively light protons, the LHC at the European Research Center CERN in Geneva, for the first time accelerated heavy lead ions and brought them to collision. The heavy ion pre-accelerator that is crucial for today’s LHC operation was developed and built by GSI Helmholtzzentrum für Schwerionenforschung. Furthermore, GSI is significantly involved in the ALICE experiment, one of the four large international experiments at LHC. ALICE was developed in particular to measure reactions between heavy ions at high energies and, today, recorded the first particle collisions. The energy produced in a central hit of atomic nuclei set a new world record – 15 times higher than the hitherto top mark generated at the RHIC accelerator in Brookhaven, USA.

“ALICE is specially-designed for the collision of heavy nuclei. By colliding lead nuclei, we want to recreate for the smallest instant the extremely hot and dense plasma state of quarks and gluons that occurred in first split seconds after the big bang.”, explains professor Peter Braun-Munzinger, director of the ExtreMe Matter Institute EMMI at GSI Helmholtzzentrum. “The measurements will give us new and unique access to so far unexplored realms of physics.”

ALICE is composed of a number of individual components and all of them are working faultlessly. Its detector is 25 meters long, 16 meters wide and 16 meters high. It functions like a three-dimensional camera and takes snapshots of the heavy ion collisions, which create thousands of new particles. Its resolution of 600 million pixels is equivalent to 750 megabyte of digital information. With a readout speed of 17.5 terabyte per second, many thousand events can be recorded every second.

From the beginning of the project on, GSI had a leading role in the construction and in the design of the scientific program for ALICE. The work is a collaboration of GSI and the universities of Darmstadt, Frankfurt, Heidelberg and Münster as well as the universities of applied science Cologne and Worms. Today, more than 1,000 scientists from 30 countries contribute to the ALICE collaboration. 41 of the more than 100 scientists from Germany are Ph.D. students. German researchers are involved in three of the central ALICE projects: the time projection chamber, which encloses the collision zone over a length of five meters and up to a radial distance of two and a half meters; the surrounding Transition Radiation Detector; and the so-called High Level Trigger, a new high performance computer, that is able to analyze the vast amount of information produced by each ALICE event in just a split second.

View of the ALICE-experiment
Visualisation of a particle collision of lead nuclei
View of the ALICE-experiment at CERN in Geneva.
Visualisation of a particle collision of lead nuclei at LHC on November 8, 2010, measured by ALICE. The picture shows a three-dimensional rotated visualisation of the measurement (yellow tracks: time projection chamber TPC; white tracks: inner tracking system ITS). The time projection chamber has a diameter of 5 meters and a length of 5 meters.
M. Brice/CERN