Alignment of the VELO pixel detector

The LHCb experiment is designed to perform high precision measurements to study CP-violation and rare decays of beauty and charm hadrons. During LS2, prior to Run 3 of the LHC, the LHCb detector will go through a major upgrade. One of the sub-detectors that will be upgraded is the Vertex Locator (VELO) which after the upgrade will be capable of readout at 40 MHz at a luminosity of 2· 1033 cm−2s−1. VELO is a high precision detector designed to reconstruct and discriminate between primary and secondary vertices close to the interaction point. Due to safety of the detector, the VELO is divided into two retractable halves which prior to each fill into LHC are retracted from the beam-line, and closed once stable beam is declared. Best possible performance of the VELO requires the halves of the VELO, and the individual detector elements of it, to be aligned for correct reconstruction of tracks and vertices.