Metrology results of the ALFA 2006 prototype detectors

We present the results of the metrological analysis of the ALFA scintillating fibre prototype detectors which have been developed and built for beam tests at the CERN SPS in autumn 2006. The measurements were performed with a high resolution 3D optical coordinate measurement machine. The positions of the individual fibres could be determined with an accuracy of better than 5 microns. The parameterized data served as input for a geometrical Monte-Carlo code which allowed estimating the ultimately achievable resolution of the detectors. The expected resolution of 20-23 microns fully satisfies the requirements dx = dy ~ 30 microns. The metrology data is also used as input in the hit reconstruction algorithms to analyse the data taken in the particle beam. The metrology data of the detector 2_2_64 exhibits distortions which possibly could be reduced by an improved fibre positioning and gluing procedure.