Particle identification in the NA49 TPCs

The NA49 tracking system is comprised of four large-volume Time-Projection-Chambers (TPCs) which measure the charged (and neutral strange) hadrons produced in 160 GeV Pb–Pb nuclear collisions. In typical events with multiplicities of the order of 1500 per event, the TPCs provide momentum and specific ionization information for Particle IDentification (PID) purposes. Two TPCs are located in large gap super-conducting dipole magnets, while two larger chambers sit in field free regions. In all, some 181k channels instrument the chambers. The different environments and conditions within each detector, and the fact that tracks vary in length from 0.5 to 7 m, provide a unique experimental environment in which to carry out PID in the relativistic rise. A 5% resolution in the ionization measurements is realized after extensive calibration, and off-line correction. This allows PID to be carried out on a particle by particle basis rather than in statistical ensembles.