TPC data compression

In the collisions of ultra-relativistic heavy ions in fixed-target and collider experiments, multiplicities of several ten thousand charged particles are generated. The main devices for tracking and particle identification are large-volume tracking detectors (TPCs) producing raw event sizes in excess of 100 Mbytes per event. With increasing data rates, storage becomes the main limiting factor in such experiments and, therefore, it is essential to represent the data in a way that is as concise as possible. In this paper, we present several compression schemes, such as entropy encoding, modified vector quantization, and data modeling techniques applied on real data from the CERN SPS experiment NA49 and on simulated data from the future CERN LHC experiment ALICE.