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| ATLAS Pixel | |
|---|---|
| Name | ATLAS Pixel |
| Location | CERN, Geneva |
| Detector | ATLAS |
| Experiment | Large Hadron Collider |
| Collaboration | ATLAS experiment |
| Status | Active |
| First operation | 2008 |
ATLAS Pixel is the innermost silicon tracking detector of the ATLAS experiment at the Large Hadron Collider in CERN, Geneva. It provides high-precision measurements of charged-particle trajectories used by analyses from searches for the Higgs boson to measurements of the top quark and studies of electroweak interaction processes. Designed, constructed, and operated by an international collaboration of institutions such as University of Oxford, Lawrence Berkeley National Laboratory, Institut de Física d'Altes Energies, and University of Tokyo, the detector plays a central role in the Large Hadron Collider Run 1, Run 2, and Run 3 physics programs.
The pixel detector forms part of the Inner Detector ensemble together with the Semiconductor Tracker and the Transition Radiation Tracker, surrounding the interaction point of the ATLAS detector. It was commissioned during the initial LHC startup and participated in major milestones including the observation of the Higgs boson in 2012 and precision measurements delivered by the ATLAS collaboration. The system’s proximity to the beamline subjects it to high fluences of particles produced in proton–proton collisions and necessitates radiation-hard design choices informed by work at facilities like CERN Proton Synchrotron and tests at the DESY test beam.
The detector employs hybrid silicon pixel technology originating from developments at Stanford Linear Accelerator Center, Fermilab, and the Max Planck Institute for Physics. Individual modules integrate radiation-tolerant readout chips bump-bonded to high-resistivity silicon sensors, leveraging designs influenced by projects at KEK and TRIUMF. Materials and cooling strategies draw on expertise from KIT (Karlsruhe Institute of Technology), Brookhaven National Laboratory, and University of Bonn to manage thermal loads while minimizing multiple scattering, using low-mass supports inspired by CERN R&D for upgrades like the Insertable B-Layer and future pixel systems.
The detector is arranged in concentric cylindrical layers and forward disk assemblies around the beam axis, following geometrical optimization studies with simulation frameworks developed at CERN and universities including University of Manchester and University College London. The layout balances rapid charge collection, granularity, and coverage in pseudorapidity to satisfy track-reconstruction requirements for experiments in the ATLAS cavern near the Point 1 interaction region. Mechanical design, alignment, and survey activities involved collaborations such as LAPP (Annecy) and University of Glasgow to ensure stability under thermal and mechanical stresses.
Front-end ASICs implement zero-suppression, time-stamping, and hit buffering inspired by microelectronics efforts at IRFU Saclay and CEA. Data are transmitted through high-speed optical links and handled by back-end electronics tied into the ATLAS Trigger and Data Acquisition architecture, coordinating with the Level-1 trigger and the High-Level Trigger. Firmware and software development was undertaken by teams at institutions including SLAC National Accelerator Laboratory, Columbia University, and Universität Zürich to integrate with global dataflow systems used during LHC Run 2 and beyond.
Performance metrics such as hit efficiency, spatial resolution, and impact-parameter resolution were validated in cosmic-ray runs, test beams at CERN SPS, and early collision data analyzed by groups from University of Melbourne, University of Wisconsin–Madison, and Ludwig Maximilian University of Munich. Calibration procedures include threshold tuning, charge calibration, and timing alignment coordinated with the ATLAS calibration group and using techniques comparable to those developed at DESY and Paul Scherrer Institute. Radiation damage monitoring draws upon dose measurements used in radiation-hard electronics programs at CERN and long-term annealing studies performed with collaborators at INFN.
Operational support, maintenance, and incremental improvements have been carried out during shutdowns coordinated with the LHC Long Shutdown 1 and LHC Long Shutdown 2 schedules. A notable upgrade, the Insertable B-Layer project, added a new innermost pixel layer developed by consortia including University of Edinburgh, University of Liverpool, and Nikhef. Future upgrade programs tie into the High-Luminosity LHC upgrade path and involve international partners such as CEA, CERN, and DESY to develop radiation-hard sensors, advanced cooling, and readout electronics for the Phase-II upgrade.
Data from the pixel detector underpin vertex reconstruction, b-tagging algorithms, and searches for displaced vertices used in analyses by the ATLAS collaboration investigating the Higgs boson couplings, rare Standard Model processes, and searches for physics beyond the Standard Model including supersymmetry and exotic long-lived particles. Results leveraging pixel-based tracking contributed to precision measurements reported alongside work from collaborations at CMS, combined measurements with experiments like LHCb, and collaborative endeavors in the wider particle-physics community involving institutions such as Imperial College London, CERN Theory Division, and Institut de Physique Nucléaire d'Orsay.
Category:ATLAS detector Category:Particle physics detectors Category:CERN experiments