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HK: Fachverband Physik der Hadronen und Kerne

HK 30: Instrumentierung V

HK 30.7: Vortrag

Dienstag, 16. März 2010, 18:15–18:30, HG VIII

ALICE HLT Tracker — •Sergey Gorbunov — Frankfurt Institute for Advanced Studies, Frankfurt — Kirchhoff Institut für Physik, Heidelberg

The on-line event reconstruction in ALICE is performed by the High Level Trigger, which should processes up to 2000 events per second in proton-proton collisions and up to 200 central events per second in heavy ion collisions, corresponding to an input data stream of 30 GB/s.

In order to fulfil the time requirements, a fast on-line tracker has been developed. The algorithm combines a Cellular Automaton method, which is used for a fast pattern recognition, and the Kalman Filter method, which performs a fit of found trajectories and the final track selection.

The on-line algorithm has proved its high performance (99.9% for the proton-proton events and 95.8% for the central Pb-Pb collisions) in comparison with the off-line reconstruction (99.9% and 95.8% correspondingly). In addition to the the high efficiency, the on-line reconstruction is an order of magnitude faster than the off-line analysis: 19.6ms (pp) or 17.6s (PbPb central) in comparison with 66.0ms or 160.1s for the off-line.

An important feature of the on-line algorithm is an ability to use GPU hardware accelerators, giving another order of magnitude speed-up for the data processing. The GPU tracker is integrated to the High Level Trigger framework and is used for the on-line event reconstruction in the ALICE experiment.