LHCb vertex locator commissioning and results from the first LHC beam reconstructed tracks

LHCb is a dedicated experiment at the LHC to study CP violation and rare b-quark decays. The vertex locator (VELO) is a silicon strip detector designed to measure precisely the production and the decay vertices of B-mesons. The VELO consists of two retractable detector halves with 21 silicon micro-strip tracking modules each. The full system has been operated since June 2008 and its commissioning experience is reported. During the LHC synchronization tests in 2008, LHCb detectors measured particles produced by the interaction of the LHC primary beam on an absorber. About 2200 tracks were reconstructed in the VELO and they were used for the first evaluation of the alignment. A single hit resolution of 10 μ m was obtained at the smallest pitch for tracks of perpendicular incidence. The design and the main components of the detector system are introduced, focusing on the commissioning of the detector and on the results of the measurements of the first tracks in the VELO.