First results on the NA60 pixel detector

The NA60 experiment is taking place at the CERN SPS, to study the production of open charm and of prompt dimuons in collisions induced by proton and heavy ion beams on nuclear targets. Downstream of the target system and inside a dipole magnetic field of 2.5 T we have a silicon vertex telescope that tracks the charged particles and allows us to match them with the muons measured in the muon spectrometer. For proton runs this telescope can be made of silicon microstrip planes whereas for ion runs the high multiplicity of charged particles imposes the exclusive use of silicon pixel detectors. We are preparing a pixel telescope with 16 pixel planes made with 88 radiation hard ALICE1LHCb pixel readout chips. The ten planes closest to the target are made of four chips, while the other six planes are made of eight-chip substrates grouped in three double planes. After operating a first four-chip plane in a proton run in June 2002, three four-chip planes were exposed to Pb-Pb collisions in October 2002. This paper gives a description of the NA60 pixel telescope as well as an overview of the first results obtained from the data collected in the October heavy ion run.