CMS Tracker
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| CMS Tracker | |
|---|---|
| Name | CMS Tracker |
| Introduced | 2008 |
| Location | CERN |
| Associated | Large Hadron Collider |
| System | Compact Muon Solenoid |
CMS Tracker is the inner silicon tracking detector of the Compact Muon Solenoid experiment at the Large Hadron Collider housed in the CERN laboratory near Geneva. It measures trajectories of charged particles produced in collisions from the LHC and provides precision vertexing for studies involving the Higgs boson, top quark, and searches for supersymmetry and dark matter. The Tracker interfaces with the CMS Electromagnetic Calorimeter, CMS Hadron Calorimeter, and the CMS Muon System to enable comprehensive event reconstruction for collaborations such as ATLAS and LHCb during comparative analyses.
Overview
The Tracker is a cylindrical silicon detector array surrounding the Interaction point at CMS and was installed for Run 1 and Run 2 of the LHC. It complements subsystems like the Trigger system and the Data Acquisition system and works with experiments such as ALICE for cross-calibration studies. The design supports measurements used in discoveries at the CERN Large Hadron Collider including the 2012 observation attributed to the ATLAS and CMS collaborations. The device operates within the CMS magnet cryostat environment and must withstand radiation patterns characterized in studies by Particle Data Group working groups.
Design and Components
The Tracker is composed of layers of silicon pixel detectors and silicon strip detectors arranged in a barrel and endcap geometry. Pixel modules were developed in collaborations involving BaBar, Belle II, FNAL, Brookhaven National Laboratory, Fermilab, and INFN. Strip modules were produced by institutions like CNRS, DESY, KEK, and IHEP. Readout electronics include ASICs influenced by designs from ATLAS IBL projects and employ cooling linked to systems used at LHCb and ALICE ITS. Mechanical supports reference engineering methods from Large Hadron Collider beauty projects and the CERN Detector Laboratory. Power distribution follows practices tested at SLAC National Accelerator Laboratory and TRIUMF. Mounting and alignment use survey techniques from European Organization for Nuclear Research divisions and heritage from LEP detectors.
Performance and Upgrades
Initial Tracker performance met specifications for track resolution and impact parameter precision critical for reconstructing decays like B meson oscillations and isolating signatures of the Higgs boson decaying to b quark pairs. Upgrades planned for High-Luminosity LHC runs incorporated lessons learned from the Insertable B-Layer installation in ATLAS and from pixel upgrades at ALICE. The upgrade roadmap involved institutions such as CERN, KEK, Fermilab, Brookhaven National Laboratory, INFN, DESY, IHEP, and SLAC and drew on sensor R&D demonstrated in collaborations like CMS Phase-2 projects. Radiation-hard technologies referenced developments from RD53 consortium and tests at irradiation facilities such as PSI and CNA.
Reconstruction and Software
Tracking reconstruction uses software frameworks developed within the CMS Collaboration and integrates with the CMSSW release series and the ROOT data analysis framework. Pattern recognition algorithms were benchmarked against techniques from Kalman filter implementations used in experiments like ZEUS and H1. Track fitting and vertexing utilize packages interoperable with Geant4 simulation outputs and are validated with datasets from Run 1 and Run 2. Offline computing for reconstruction leverages the Worldwide LHC Computing Grid and contributions from centers such as CERN IT Tier‑0, Fermilab Tier‑1, KIT Tier‑1, and PIC Tier‑1. Software quality and continuous integration are managed with tools and workflows inspired by practices at GitHub, GitLab, and CERN OpenLab partnerships.
Alignment and Calibration
Precision alignment uses cosmic-ray campaigns and collision data, employing procedures comparable to alignment strategies in ATLAS and LHCb. Calibration constants for Lorentz angle and gain follow measurements cross-checked with testbeams at CERN SPS and irradiation studies at TRIUMF and PSI. Laser alignment systems and optical surveys relied on metrology techniques developed with partners like CMM facilities and national metrology institutes such as NPL and PTB. Alignment campaigns were coordinated with commissioning phases during Run 1 and Run 2 and integrated into offline workflows for physics analyses including measurements of the W boson mass and searches for rare decays.
Operational History and Experiments
Operational history spans installation prior to the LHC Run 1 start, performance during the 7 and 8 TeV runs, and continued service through 13 TeV data-taking in Run 2. The Tracker enabled key CMS publications on the Higgs boson discovery, measurements of the top quark pair production cross section, and limits on supersymmetric particles. It supported heavy-ion collision analyses in coordination with ALICE and measurement programs involving the Quark–Gluon Plasma. Maintenance and upgrade operations involved logistics with CERN Accelerator Complex scheduling and safety coordination with CERN Radiation Protection and international funding from agencies such as NSF, DOE, ERC, INFN, DFG, and JSPS.