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Abstract: LHCb is the dedicated heavy flavour experiment at the Large Hadron Collider at CERN. The partially assembled silicon vertex locator (VELO) of the LHCb experiment has been tested in a beam test. The data from this beam test have been used to determine the performance of the VELO alignment algorithm. The relative alignment of the two silicon sensors in a module and the relative alignment of the modules has been extracted. This alignment is shown to be accurate at a level of approximately and for translations and rotations, respectively, in the plane of the sensors. A single hit precision at normal track incidence of about is obtained for the sensors. The alignment of the system is shown to be stable at better than the level under air to vacuum pressure changes and mechanical movements of the assembled system. [Copyright &y& Elsevier]

Abstract: LHCb is one of the four main experiments of the Large Hadron Collider (LHC) project, which will start at CERN in 2008. The experiment is primarily dedicated to B-Physics and hence requires precise vertex reconstruction. The silicon vertex locator (VELO) has a single hit precision of better than and is used both off-line and in the trigger. These requirements place strict constraints on its alignment. Additional challenges for the alignment arise from the detector being retracted between each fill of the LHC and from its unique circular disc strip geometry. This paper describes the track-based software alignment procedure developed for the VELO. The procedure is primarily based on a non-iterative method using a matrix inversion technique. The procedure is demonstrated with simulated events to be fast, robust and to achieve a suitable alignment precision. [Copyright &y& Elsevier]