CMS DAQ

CMS DAQ
Name	CMS DAQ
Established	1990s
Location	CERN
Type	High-energy physics data acquisition

CMS DAQ

The Compact Muon Solenoid (CMS) data acquisition system collects, buffers, formats, and transports detector readout for analysis in the Large Hadron Collider environment. It interfaces with front-end electronics, global trigger systems, and offline storage to enable physics programs such as searches for the Higgs boson, studies of top quark, and precision measurements involving the Standard Model. The system operates within the CERN experimental infrastructure and integrates with control and monitoring frameworks used across projects like ATLAS and LHCb.

Overview

The DAQ is central to the CMS experiment at the Large Hadron Collider, responsible for handling event rates generated by collisions in the Compact Muon Solenoid detector. It bridges front-end readout housed in detector subsystems including the Silicon Tracker, Electromagnetic Calorimeter (CMS), Hadron Calorimeter (CMS), Muon System (CMS), and specialized systems such as the Forward Hadron Calorimeter and Pixel Detector. The DAQ interacts with trigger systems including the Level-1 trigger and High-Level Trigger while coordinating with timing and synchronization services like the Beam Synchronous Timing distribution and the Worldwide LHC Computing Grid for downstream processing.

Historical Development

The DAQ evolved from early test-beam readout prototypes at facilities like CERN PS and CERN SPS to a full experiment-wide system deployed for LHC Run 1 and Run 2. Key milestones include integration during the CMS Tracker Integration Workshop, commissioning in the LHC machine start-up with the LHC 2008 commissioning, and operation through major discoveries such as the observation announced by collaborations involving Fabiola Gianotti and institutes like Institut de Physique des Hautes Energies and Fermilab. Iterative upgrades were planned in coordination with the LHC Upgrade projects and the High-Luminosity LHC initiative, following roadmaps discussed at workshops with participants from Brookhaven National Laboratory, Lawrence Berkeley National Laboratory, and DESY.

System Architecture

The architecture is layered, combining front-end electronics, readout units, event builders, filter farms, and archival interfaces. It uses standards and technologies adopted across high-energy physics such as S-LINK, PCIe, and network fabrics akin to those developed by Mellanox Technologies and standards bodies like the Institute of Electrical and Electronics Engineers. Control and configuration subsystems draw on frameworks used by experiments at CERN and international laboratories such as IHEP and KEK. The DAQ topology supports modular expansion to respond to detector upgrades designed at institutions including University of California, San Diego and University of Wisconsin–Madison.

Data Flow and Triggering

Collision data are selected in stages: initial selection by the Level-1 trigger hardware followed by software filtering in the High-Level Trigger running on a computing farm. The DAQ manages buffering in readout units and event-building operations that assemble fragments from subsystems like the Barrel ECAL and Endcap ECAL into full events. Trigger menus and selection criteria are developed and validated by teams at organizations such as Princeton University, University of Oxford, Imperial College London, and CERN PH. Data then flow to storage elements of the Worldwide LHC Computing Grid via transfer services coordinated with Tier-0 (CERN) and regional Tier-1 centers including CNAF and Rutherford Appleton Laboratory.

Hardware Components

Key hardware elements include front-end readout ASICs, concentrator cards, readout units, event builder switches, and processing nodes. Components derive from designs by collaborations involving FNAL, SLAC National Accelerator Laboratory, Institute for High Energy Physics (Protvino), and commercial vendors such as Intel and AMD. Precision timing and clock distribution are provided by systems compatible with White Rabbit and IEEE 1588 implementations. Data links use optical transceivers following standards promoted by groups like the OPERA collaboration and vendors in the Telecommunications Industry.

Software and Control Systems

DAQ control uses online software frameworks integrating run control, configuration databases, and monitoring derived from tools developed at CERN IT and contributed by universities like ETH Zurich and University of Manchester. Middleware components include message passing, logging, and telemetry systems interoperable with SCADA-style consoles and experiment-wide services such as Database for Conditions and Calibration Workflows. Trigger algorithms are implemented within frameworks shared across experiments, and deployment utilizes containerization and orchestration approaches known from projects at Google and Red Hat.

Performance and Operational Experience

Operational performance is documented through metrics like sustained throughput, deadtime, and data quality monitored by teams from institutions including University of California, Santa Barbara, Massachusetts Institute of Technology, CERN EP groups, and ETH Zurich. The DAQ has supported high-profile running conditions during campaigns such as LHC Run 1, LHC Run 2, and machine developments coordinated with the CERN Accelerator Complex. Lessons learned influenced upgrades and risk mitigation strategies studied with partners like CERN Safety Commission and computing centers such as KIT.

Upgrades and Future Plans

Planned upgrades align with the High-Luminosity LHC schedule, emphasizing higher bandwidth fabrics, enhanced event-building architectures, and tighter integration with trigger processing using accelerators like GPUs and FPGAs. R&D involves collaborations across laboratories including CERN, Fermilab, Brookhaven National Laboratory, DESY, and universities such as University of Geneva and Vrije Universiteit Brussel. Future DAQ iterations will address challenges posed by increased pileup during HL-LHC operations and will interface with evolving computing models driven by projects like the European Open Science Cloud.

Category:Compact Muon Solenoid Category:Data acquisition systems Category:Large Hadron Collider