Calibrations of two alignment sensors used in the ATLAS barrel muon spectrometer

ATLAS is a particle detector which will be built at CERN (Geneva) at the Large Hadron Collider (LHC) accelerator. The ATLAS barrel muon spectrometer is made up by 600 chambers positioned in three layers embedded in a toroidal magnetic field. Thus each muon track is detected by three muon chambers within a projective tower performing a sagitta measurement. In order not to deteriorate the sagitta measurement, the muon chamber position must be known within a tower with a spatial resolution of 30μm. To fulfill these requirements. different optical alignment systems have been built. In the ATLAS barrel spectrometer, six different alignment types participate to the global alignment. Among them the PRAXIAL and REFERENCE sensors have been developed at Saclay. A short introduction on the alignment of the experiment is given in the first section, the second and third sections are devoted to the PRAXIAL system calibration. The fourth section describes the REFERENCE alignment systems. The last part is related to the user interlace that manages all alignment calibration benches.