ALICE : A Large Ion Collider Experiment
ALICE is A Large Ion Collider Experiment currently in operation at the Large Hadron Collider (LHC) at the European Centre for Particle Physics CERN near Geneva.
While ALICE is also running and taking data for collisions of protons, it is primarily designed for operation with collisions of heavy-ions, mainly lead-nuclei. The primary aim of this experiment is to study the physics of strongly interacting matter at very high particle densities and temperatures to reach extreme energy densities. Under these conditions the formation of a state of matter, the quark-gluon-plasma (QGP), is expected that is assumed to have existed shortly after the Big Bang. The existence of this state of matter, as well as its precise properties, are key issues in the physical theory of Quantum-Chromo-Dynamics (QCD).
In heavy-ion collisions up to around 10,000 particles are expected in the experiment for one collisions, leading to large data volumes of more than 80 MB per collision at collision rates of up to 8 kHz. With these large data volumes it becomes unfeasible to store the complete data of all collisions on tape for analysis. Therefore a hierarchy of complex and fast trigger systems becomes necessary to select only those collisions with the most interesting physics content.
The Chair for High Performance Computer Architecture is involved in both the TRD Trigger, a dedicated hardware trigger located directly on the TRD detector, as well as the High Level Trigger, a large cluster of Linux computers and the last stage of the trigger hierarchy.