The NA60 vertex telescope for particle tracking in heavy-ion and proton-nucleus collisions

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 vertex telescope 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 telescope was upgraded with ATLAS pixel detector modules to cope with the higher interaction rates in this run. This paper describes the setup of the pixel telescope and summarises results concerning detector performance and radiation damage.