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NA49 Tracking

A central collision of a lead projectile with a lead nucleus as recorded by the four large volume Time Projection Chambers (TPCs) of the NA49 fixed target experiment. The 150 GeV per nucleon 208Pb beam from the SPS (total energy 32.8 TeV), coming from the lower left in the picture, interacts with the target 80 cm in front of the first TPC. For momentum determination the first two TPCs are placed inside superconducting magnets of 1.5 and 1.1 T field strength.

Over 80% of the 2000 charged particles created in central events produce tracks in the sensitive volume of the detectors. Their ionization drifts up to the readout chambers, shown as small rectangles, on the top of the detectors. A total of 182,000 readout pads record 512 time samples each for the drifting ionization. Space points, shown here is red, are reconstructed into tracks, purple, and matched over the different TPCs to global tracks, yellow, of up to 14 m length with an accuracy better than 200 microns. The specific ionization for long tracks is determined with better than 4% resolution, permitting particle identification in the relativistic rise region of energy loss.

The aim of the experiment is to study the non-perturbative QCD processes leading to the production and decay of the large partonic systems formed in central Pb+Pb collisions, reaching energy densities 20 times normal nuclear density for a brief instant of time.

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