The cryogenic silicon Beam Tracker of NA60 for heavy ion and proton beams

The cryogenic silicon Beam Tracker of NA60 is the first detector based on the Lazarus effect used in a high-energy physics experiment. It employs single-sided silicon strip sensors of 50 μm pitch operated at a temperature of 130 K. Two tracking stations determine the transverse coordinates of the interaction point at the target with 20 μm resolution, to improve the determination of the offset of secondary vertices. This impact parameter measurement allows NA60 to distinguish between prompt dimuons and muon pairs from D-meson decays. The detector concept and technical feasibility have been demonstrated in beam time periods between 1999 and 2002.