The LHCb VELO detector: Design, operation and first results

Abstract

The design, operation and first results from the LHCb (Large Hadron Collider Beauty) experiment Upgrade I VELO (VErtex LOcator) are presented. The Upgrade I VELO, first installed in 2022, is a crucial new detector for providing tracking during Runs III and IV of the LHC (Large Hadron Collider). The VELO, consisting of 52 modules, closes to within 5.1 mm of the beamline. Each VELO module is made up of 4 sensors with 3, 130 nm CMOS ASICs per sensor providing precise tracking (Alves et al., 2013). The modules have a novel bi-phase CO₂ cooling substrate for reducing the radiation length of the detector while providing cooling under vacuum down to $-30°$C. A new FPGA based SuperPixel clustering firmware reduces the data-rate by approximately 30% and is the first use of FPGA clustering in a collider experiment. During the VELO 2022–2024 commissioning period the SuperPixel performance has been validated, showing consistent rates between the packet rate and reconstructed clusters. The VELO material has been mapped confirming the safe re-installation of the RF (Radio Frequency) foil with respect to the VELO modules. Per-pixel equalisation across 41M channels has also been completed successfully reaching the design threshold of 1000 $e^{-}$.