Abstract
The Vertex Locator is a silicon microstrip detector which provides the LHCb experiment with high precision measurements of tracks and decay vertices. The VELO sensors are exposed to a radiation dose of (2.5 — 6.5) × 1013 neq/cm2 per fb−1 in the area which is most irradiated. A best hit resolution of 4μm; is obtained for angled tracks, in agreement with expectations. The VELO has a vertex position resolution down to 11μm; in the transverse direction and an excellent momentum dependent performance.
Highlights
The Vertex Locator is a silicon microstrip detector which provides the LHCb experiment with high precision measurements of tracks and decay vertices
The VELO modules are contained in a secondary vacuum chamber which is separated from the main LHC vacuum by a 300 μm thick aluminium foil
Signals from the VELO sensors are read out by a radiation-hard front-end chip called the Beetle [3], which samples the charge in each strip every 25 ns
Summary
The main subsystems of the VELO detector are high voltage, low voltage, cooling, vacuum, motion and data acquisition. The VELO modules are contained in a secondary vacuum chamber which is separated from the main LHC vacuum by a 300 μm thick aluminium foil. The foil protects the LHC vacuum from outgassing from the modules and kapton cables, and prevents RF interference from the beams from affecting the sensors. The closing procedure is iterative, such that at each step the beam position is measured, the VELO modules are moved towards and centred around the beam. Data from the VELO itself, temperature and pressure sensors, and the beam position monitors are checked before proceeding to the step. Reconstructed vertices from the VELO are used to measure the beam position. Closing of the VELO is fully automated and takes less than 4 minutes
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