The NA60 silicon pixel tracker

NA60 is a fixed target experiment at the CERN SPS designed to study the production of open charm and prompt dimuons in proton–nucleus and heavy-ion collisions. To access the kinematics of the charged particles produced in the collisions already at the vertex level, a tracker made from radiation-tolerant silicon pixel detectors has been placed inside a 2.5 T magnetic field close to the target. In 2003 the vertex spectrometer, made from 12 tracking planes with 96 ALICE1LHCb pixel chips, was successfully operated in a run with a 158 GeV/nucleon indium ion beam incident on indium targets. During the five weeks of data taking, the detector was exposed to high and inhomogeneously distributed radiation levels. For the 2004 proton run, the tracker was upgraded with ATLAS pixel detector modules, to allow higher interaction rates.