Inner Tracking System upgrade

Inner Tracking System upgrade
Name	Inner Tracking System upgrade

Inner Tracking System upgrade The Inner Tracking System upgrade was a comprehensive replacement and enhancement of a silicon-based particle tracking detector carried out to improve precision tracking, vertexing, and particle identification in a high-luminosity collider environment. It addressed limitations encountered with the original detector during prolonged operation by adopting advanced pixel technologies, lightweight materials, and modern readout electronics to sustain performance under increased interaction rates and radiation levels.

Background and Motivation

Upgrades were motivated by performance degradation observed in long-term campaigns at facilities such as CERN, Brookhaven National Laboratory, Fermi National Accelerator Laboratory, DESY, and accelerator programs like the Large Hadron Collider and Relativistic Heavy Ion Collider. Experience from experiments including ATLAS experiment, CMS experiment, ALICE experiment, LHCb experiment, and successor proposals from collaborations tied to Compact Muon Solenoid and ALICE collaborations highlighted challenges with aging sensors, radiation damage, and readout bottlenecks. Funding and strategic reviews by agencies including European Research Council, United States Department of Energy, Japan Society for the Promotion of Science, and national laboratories informed upgrade roadmaps tied to runs such as LHC Run 3 and planned high-luminosity phases like High-Luminosity Large Hadron Collider planning. Lessons from detector projects such as BaBar experiment, Belle experiment, SuperKEKB, and upgrades at KEK fed into risk assessments and design choices.

Design and Technology

The upgrade adopted technologies pioneered in projects like Monolithic Active Pixel Sensors developments from institutions such as Institut Pluridisciplinaire Hubert Curien, INFN, CERN Microelectronics Group, and university groups at University of Geneva, University of Bologna, and University of Liverpool. Design studies benchmarks referenced simulation frameworks derived from GEANT4 and reconstruction toolkits used by ROOT and supported by computing centers in the Worldwide LHC Computing Grid. Cooling solutions leveraged lessons from microchannel cooling work at Paul Scherrer Institute and lightweight support structures drew on composite expertise from European Organization for Nuclear Research partners and industrial vendors contracted through procurement offices at European Commission programs. Radiation-hard readout ASIC development was coordinated with microelectronics groups at CEA and STMicroelectronics.

Detector Components and Layout

The upgraded system comprised concentric layers of silicon sensors: inner layers using monolithic or hybrid pixel detectors inspired by developments at Istituto Nazionale di Fisica Nucleare, mid layers employing fast CMOS sensors from collaborations at University of Geneva and CERN, and outer layers using double-sided silicon strip detectors building on designs used by ATLAS Inner Detector and CMS Tracker. Mechanical supports and services were modeled after successful deployments at ALICE Inner Tracking System and informed by integration experience from NA62 experiment. Precision alignment used metrology techniques developed with partners at DESY and CERN Survey Group while power distribution and low-mass cabling followed standards from RD53 Collaboration and test campaigns at GSI Helmholtz Centre for Heavy Ion Research.

Performance Goals and Simulations

Primary performance goals targeted improvements in impact parameter resolution, secondary vertex finding, momentum resolution at low transverse momentum, and tracking efficiency under pileup conditions characteristic of High-Luminosity Large Hadron Collider scenarios. Simulation campaigns used software stacks maintained by ALICE Software Group, ATLAS Collaboration, CMS Collaboration, and computing resources at CERN OpenLab and national grids coordinated with PRACE centers. Validation studies compared expected performance to benchmarks established in results from Heavy Ion Collisions runs and precision measurements such as quarkonia spectroscopy performed by ALICE experiment and flavour-tagging analyses common to LHCb experiment. Radiation tolerance targets referenced proton, neutron, and ion fluence measurements documented by CERN Radiation Protection Group and test results from irradiation facilities at TRIUMF, Jožef Stefan Institute, and Brookhaven National Laboratory.

Installation and Commissioning

Installation sequences were planned with civil and accelerator teams from CERN and national laboratories to align shutdown windows in LHC Long Shutdown 2 and subsequent technical stops used by experiments like ALICE and CMS. Commissioning procedures reused alignment and calibration workflows from ATLAS Inner Detector deployments and involved beam-based alignment runs coordinated with LHC Machine Committee and luminosity calibration groups such as ATLAS Luminosity Group. Detector control systems integrated middleware developed in collaboration with EPICS contributors and quality assurance labs at Paul Scherrer Institute and university consortia. Commissioning milestones included cooling validation, optical link performance tests with partners at CERN Optical Links Group, and first-track reconstruction checks cross-referenced with datasets from LHCb early physics runs.

Operational Experience and Upgrades

Operational experience documented improvements in data quality, track multiplicity handling, and reduced fake-track rates, reflecting contributions from institutions like CERN, INFN, CEA Saclay, University of Bonn, and the Max Planck Society. Challenges encountered included single-event upsets mitigated through firmware updates developed by RD53 Collaboration teams and increased maintenance interventions coordinated with CERN Accelerators and Beams and detector safety groups. Subsequent iterations and mid-term upgrades drew on R&D funded by European Research Council grants and national science agencies, adopting improved ASIC revisions and revised cooling manifolds tested at facilities such as DESY Test Beam and CERN PS East Area.

Impact on Physics Program and Results

The upgrade enabled higher-precision measurements in heavy-flavor physics, quark–gluon plasma characterization, and rare decay searches pursued by collaborations including ALICE experiment, CMS experiment, ATLAS experiment, and LHCb experiment. Enhanced vertexing improved charm and beauty hadron reconstruction used in analyses cited by publications from Physical Review Letters and Journal of High Energy Physics authored by teams at CERN and partner universities like University of Padua and University of Birmingham. Results contributed to global efforts in precision electroweak studies, parton distribution function constraints used by groups at CTEQ, and inputs to theoretical work by researchers at Institute for Advanced Study and institutes such as CERN Theory Department.

Category:Particle detectors