The LHCb VELO (VErtex LOcator) and the LHCb VELO upgrade

Abstract

LHCb is a forward spectrometer experiment dedicated to the study of new physics in the decays of beauty and charm hadrons produced in proton collisions at the Large Hadron Collider (LHC) at CERN. The VErtex LOcator (VELO) is the silicon detector surrounding the LHCb interaction point. The beauty and charm hadrons are identified through their flight distance in the Vertex Locator (VELO), and hence the detector is critical for both the trigger and the offline physics analyses. The sensors, which have an inner radius of ∼7mm from the beam axis at the edge, and the first sensitive strips at a radius of ∼8.2mm are exposed to maximum radiation doses of ∼0.6×10141MeVneq/cm2 per integrated luminosity of fb−1. The performance of the VELO during the first two years of LHC running is described, together with the methods used to monitor radiation damage. The detector so far shows no significant performance degradation, however many interesting effects have been observed in the sensors, including a coupling of charge to the second metal routing line layer after irradiation. In 2018 the VELO will be upgraded together with the rest of the LHCb detector to a 40MHz readout. The modules together with their front end electronics will be completely replaced with a radiation hard system capable of driving the signals out at the required rates. The current status of the R&D for the LHCb VELO Upgrade is outlined.