ATLAS ITk

ATLAS ITk
Name	ITk
System	Inner Tracker
Project	ATLAS
Location	CERN
Status	Commissioning
Detectors	Silicon pixel, Silicon strip
Predecessor	Inner Detector

ATLAS ITk The ITk is a next-generation Inner Tracker upgrade for the ATLAS experiment at CERN designed for the High-Luminosity Large Hadron Collider (HL-LHC). It replaces the current Inner Detector to provide improved tracking, vertexing, and pattern recognition in the high-pileup environment anticipated during HL-LHC runs, seeking to preserve ATLAS sensitivity to processes studied by collaborations such as CMS, LHCb, and ALICE.

Introduction

The upgrade responds to projected luminosity and pileup conditions from the HL-LHC, a program led by CERN and coordinated among projects including LHC, HL-LHC Project, European Organization for Nuclear Research, and participating institutions from countries such as United Kingdom, France, Germany, Italy and United States. It interfaces with experiments and initiatives like ATLAS experiment, CMS experiment, Detector R&D, High Energy Physics laboratories, and funding agencies including European Research Council, Science and Technology Facilities Council, and national laboratories such as Fermilab and Brookhaven National Laboratory. The project follows milestones established by bodies such as the LHC Long Shutdown 3 timeline and adheres to safety and technical standards from organizations like IEEE, CERN Safety Policy, and technical review panels convened by the CERN Research Board.

Design and Architecture

The ITk architecture comprises a multi-layered silicon pixel system and an outer silicon strip system arranged in a cylindrical barrel and forward endcap geometry, with mechanical support and services designed by teams from institutions including University of Oxford, University of Manchester, CERN PH Department, Max Planck Institute for Physics, and INFN. Its mechanical design addresses constraints from the ATLAS magnet system, Tile Calorimeter, Liquid Argon Calorimeter, and integration envelopes defined by the ATLAS Insertable B-Layer experience and technical interfaces with the ATLAS muon spectrometer. Electronics architecture integrates front-end ASICs, service routing, and opto-electronics developed in collaboration with industry partners and groups from CNRS, CEA Saclay, KEK, and SLAC National Accelerator Laboratory.

Silicon Pixel Detector

The pixel detector employs hybrid and monolithic technologies with high-granularity sensors arranged in concentric layers and forward disks to provide precise impact parameter resolution, developed by consortia from University of Birmingham, University of Edinburgh, Imperial College London, University of Tokyo, and University of Melbourne. Readout uses ASIC families and protocols stemming from work at CERN Microelectronics, ON Semiconductor, AMS AG, and TSMC, and leverages radiation-tolerant design techniques informed by studies at PSI, DESY, and the European XFEL. Pixel modules optimize material budget and cooling interfaces influenced by studies at ATF2, RAL, and collaborative testbeams at facilities such as CERN SPS, Fermilab Test Beam Facility, and DESY Test Beam.

Silicon Strip Detector

The strip detector complements the pixel system with long-strip sensors and stereo modules providing extended tracking coverage and momentum measurement, developed by groups at University of California, Berkeley, University of Geneva, University of Liverpool, NIKHEF, and University of Bonn. Sensor fabrication builds on technology from Hamamatsu Photonics, CiS Forschungsinstitut, and collaborative prototyping informed by test campaigns at CERN Irradiation Facility, TRIUMF, and GSI Helmholtz Centre. Module assembly uses automated gantry systems and metrology standards from VTT Technical Research Centre of Finland, Fraunhofer Society, and industrial partners to meet mechanical tolerances and quality assurance procedures shaped by the ATLAS Upgrade Steering Committee.

Trigger and Data Acquisition Integration

ITk interfaces with the ATLAS Trigger and Data Acquisition (TDAQ) system to provide tracking information to the Level-0/Level-1 decision layers and high-level trigger algorithms developed by teams from ATLAS TDAQ, CERN IT Department, CSCS, FNAL, and Purdue University. Data links use high-speed optical transceivers and protocols standardized by collaborations with HEP Electronics, GÉANT, and industry partners such as Broadcom and Finisar, while firmware and software stacks integrate with frameworks like Athena, Gaudi, ROOT, and the Worldwide LHC Computing Grid for prompt reconstruction and offline analysis.

Radiation Hardness and Cooling Systems

The design addresses extreme radiation fluences and Total Ionizing Dose (TID) levels using radiation-hard sensor technologies, qualified via irradiation campaigns at CERN CHARM, TRIGA, KIT, and SCK CEN, with contributions from materials groups at Imperial College, ETH Zurich, and University of Copenhagen. Cooling employs evaporative CO2 systems inspired by deployments in LHCb VELO, CMS Tracker Upgrade, and industrial refrigeration expertise from partners like Johnson Controls and Schneider Electric, integrated into thermal studies and finite-element simulations validated by ANSYS and experimental thermal benches.

Construction, Commissioning, and Performance

Construction follows distributed production models with module fabrication across institutions such as University of Liverpool, Monash University, University of California, Santa Cruz, and Tsinghua University, subject to QA workflows overseen by the ATLAS Upgrade Project Board. Commissioning leverages cosmic-ray runs, laser alignment systems, and beam-based alignment during LHC Run 4 preparations with validation at CERN SPS and performance metrics compared to legacy systems like the ATLAS Inner Detector, demonstrating improvements in track reconstruction efficiency, fake-rate reduction, and primary-vertex resolution critical for analyses pursued by collaborations studying Higgs boson, top quark, and searches for supersymmetry.

Collaboration and Project Management

The ITk effort is organized under the ATLAS Upgrade governance with coordination among institutional boards, technical coordinators, and physics groups drawn from universities and laboratories including University of Chicago, Columbia University, University of Wisconsin–Madison, Kyoto University, Seoul National University, and agencies such as DOE, NSF, European Commission, and national research councils. Project management employs review cycles monitored by the CERN Research Board, quality assurance from the ATLAS Quality Assurance Board, and outreach coordinated through channels including Science Media Centre and partner universities to disseminate results and milestones to the broader High Energy Physics community.

Category:ATLAS experiment upgrades