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| VELO (LHCb) | |
|---|---|
| Name | VELO |
| Caption | Vertex Locator (VELO) at LHCb |
| Established | 2008 |
| Location | CERN, Meyrin, Switzerland |
| Type | Silicon vertex detector |
| Owner | European Organization for Nuclear Research |
VELO (LHCb) The VELO is the silicon Vertex Locator of the LHCb experiment at CERN, designed to provide precise vertexing for studies of CP violation and rare decays in heavy-flavor physics. Installed around the interaction point of the Large Hadron Collider, VELO enables reconstruction of primary and secondary vertices for particles such as B mesons and D mesons with micrometer precision. VELO's technology, integration, and upgrades have involved collaborations with institutions including University of Oxford, Max Planck Society, and Imperial College London.
VELO serves as the innermost subdetector of the LHCb experiment, surrounding the proton–proton collision point in the Large Hadron Collider ring at CERN. It plays a central role in tracking charged particles for analyses pursued by collaborations such as LHCb Collaboration and supports measurements related to CP violation in the Standard Model and searches for physics beyond the Standard Model like supersymmetry and flavour anomalies. VELO's performance affects studies published in journals associated with organizations such as the European Physical Journal C, Physical Review Letters, and Journal of Instrumentation.
The VELO design was driven by requirements from the LHCb Technical Design Report and by input from institutions including University of Liverpool, CERN PH, and Nikhef. Mechanical design includes retractable halves to protect sensors during LHC injection and ramping, coordinated with control systems from groups such as STFC and INFN. Thermal management used evaporative CO2 cooling developed in collaboration with University of Zurich and CERN Cooling and Ventilation Group. Radiation-hard design choices referenced studies by RD50 Collaboration and manufacturers including Hamamatsu and VTT Technical Research Centre of Finland.
VELO consists of modules arranged in two retractable halves, each comprising silicon sensors, front-end electronics, and mechanics from suppliers such as NXP Semiconductors and Texas Instruments for power control. The original VELO used microstrip silicon sensors developed with contributions from Imperial College London and University of Manchester, while the upgrade employed pixel sensors based on Timepix3 and Medipix technologies influenced by CERN Microelectronics Group. Readout electronics include custom ASICs such as the Beetle and later VeloPix chips, designed by teams at University of Santiago de Compostela and CERN EP-ESE. Alignment systems used metrology techniques from National Physical Laboratory and optical survey tools from ZEISS. Radiation monitoring and beam condition instrumentation coordinated with LHC Beam Instrumentation teams and CERN Radiation Protection groups.
VELO provides primary vertex resolution comparable to expectations from the LHCb trigger requirements, achieving impact parameter resolutions that enabled precise lifetime measurements of particles like B0 and Bs mesons. Calibration workflows employed alignment algorithms developed with software from Gaudi and ROOT, and used track samples from control channels including J/psi→μ+μ− and Lambda decays. Radiation damage studies referenced irradiation campaigns at facilities such as CERN-PS and TRIUMF, with annealing studies compared to results from SLAC National Accelerator Laboratory. Cooling performance and temperature stabilization were monitored using sensors traceable to standards at Physikalisch-Technische Bundesanstalt.
During LHC operasi...