Study of the vertexing detector position using material hadronic interaction vertices at the LHCb Upgrade experiment

The LHCb experiment is one of the four large experiments at the LHC, designed to perform high precision measurements of CP Violation and rare decays of heavy avored hadrons. The alignment of the vertexing detector (VELO) is fundamental to achieve the best precision in the reconstruction of primary vertex (dened as the collision point of the two LHC beams) and secondary vertex, where the heavy avoured hadron decays. The upgraded VELO detector consists of pixel silicon sensors arranged in several modules placed on two retractable halves that close around the interaction region after the LHC beams are declared stable. During physics data taking the VELO modules have the closest approach to the LHC beams among the LHC experiments. A data-driven method to determine the module position using Monte Carlo events has been studied. In this approach, secondary interactions of hadrons are used to map the location of material in the VELO. This allows to determine, among several elements, the z-position of the modules, which is one of the key elements for a high precision measurement of the decay length of heavy avoured hadrons. Furthermore, this method makes possible to determine the global position of the VELO and to obtain an independent measurement of the alignment accuracy in data. Precise constraints on the position of the VELO modules are critically important for the high precision programme of the LHCb experiment during the upgrade data taking phase, foreseen to start at the end of 2021.