First spatial alignment of the LHCb VELO and analysis of beam absorber collision data

A first alignment of the LHCb Vertex Locator has been obtained from beam induced tracks at the LHC. A 450 GeV/c   protons were collided on a beam absorber during the LHC synchronisation tests of the anti-clockwise beam in August and September 2008. The resulting particle tracks have been reconstructed by the Vertex Locator. This was the first full reconstruction of tracks induced by the LHC beam. The quality of the data obtained is discussed. A total of 2200 tracks were reconstructed from the full data sample, and a first spatial alignment was obtained. The detector is aligned to an accuracy of 5μm in the sensor plane. The results confirm that all detector modules have not been displaced from their surveyed positions by more than 10μm.