ATLAS IBL

ATLAS IBL
Name	Insertable B-Layer (IBL)
Experiment	ATLAS
Location	CERN
Detector type	Pixel detector
Operation start	2014
Collaborators	ATLAS Collaboration
Status	Operational (as of 2024)

ATLAS IBL The Insertable B-Layer (IBL) is a precision silicon pixel layer added to the ATLAS experiment at CERN during the Large Hadron Collider (LHC) Long Shutdown 1. It was installed to improve vertexing, tracking, and b-tagging performance for analyses such as the Higgs boson coupling measurements, top quark physics, and searches for supersymmetry. The IBL project involved collaboration among institutions including University of Oxford, Lawrence Berkeley National Laboratory, University of Tokyo, INFN, and Max Planck Society.

Introduction

The IBL is a fourth pixel layer placed closest to the beam pipe inside the ATLAS Inner Detector, designed to cope with higher instantaneous luminosity from the LHC upgrade program. Its purpose was to enhance the capabilities first established by the original pixel detector that supported key discoveries like the observation of the Higgs boson in 2012 by the ATLAS Collaboration and CMS. The project required coordination with projects such as the LHC luminosity upgrade, involvement from agencies like the European Organization for Nuclear Research, and integration with ATLAS subsystems including the Transition Radiation Tracker and the Semiconductor Tracker.

Design and Construction

The IBL design responded to requirements from the LHC machine group and the High Luminosity LHC planning documents. Mechanical design, thermal management, and radiation hardness specifications were influenced by studies from CERN engineering teams and groups at KEK, DESY, and Brookhaven National Laboratory. The stave-and-module architecture was developed through prototyping campaigns involving FNAL, University of Bonn, University of Manchester, and CEA Saclay. Production used cleanroom facilities at CERN, Lawrence Berkeley National Laboratory, and partner institutes, following quality assurance protocols inspired by projects like the ATLAS Tile Calorimeter and the ATLAS Muon Spectrometer.

Detector Components and Technologies

The IBL combined planar silicon sensors and 3D silicon sensors assembled on lightweight carbon-fiber staves. Readout employed the FE-I4 front-end integrated circuit developed jointly by teams at KEK and CERN. Cooling used a bi-phase CO2 system developed in collaboration with groups from CERN and University of Glasgow to manage heat load while minimizing material budget—an engineering approach similar to that used in the LHCb VELO upgrade. Power distribution and low-voltage regulation were developed with expertise from RAL and CERN power conversion groups. Precision alignment relied on metrology techniques used by ATLAS subsystems and surveys linked to the LHC alignment database.

Installation and Integration with ATLAS

Installation required removal and replacement operations coordinated with the ATLAS technical coordination office and the LHC operations team during Long Shutdown 1. Integration challenges included compatibility with the existing ATLAS Inner Detector, routing of optical links to the ATLAS Readout System, and mechanical interfaces designed with input from the ATLAS Detector Assembly teams and the CERN Antiproton Decelerator workshop. Safety and schedule constraints were negotiated with the European Commission funding bodies and national agencies such as UK Research and Innovation and National Science Foundation.

Performance and Calibration

Commissioning used cosmic-ray runs, beam splash events from the LHC, and initial collision data to calibrate timing, charge collection, and threshold settings. Calibration procedures drew on techniques established by the ATLAS Pixel detector group and collaborations with groups at University of Geneva and Instituto de Física Corpuscular. Performance metrics included impact-parameter resolution, track reconstruction efficiency, and b-tagging improvement—benchmarked against results from analyses by the ATLAS physics groups for top quark pair production, Higgs boson decays, and exotic searches. Radiation damage studies referenced models developed by CERN Radiation Protection, Nuclear Instruments and Methods collaborations, and the RD50 collaboration.

Operational History and Upgrades

Operational since 2014, the IBL has been maintained through monitoring by the ATLAS Operations teams, periodic interventions during Long Shutdown 2 and planned upgrades for the High-Luminosity LHC era. Firmware and configuration updates were coordinated with the ATLAS Trigger and Data Acquisition teams and firmware groups at CERN and partner laboratories. Lessons from the IBL informed upgrade projects such as the ATLAS Inner Tracker (ITk) and influenced sensor R&D at KEK, FBK, and IMB-CNM.

Impact on Physics Analyses

The IBL significantly improved vertex resolution and track pattern recognition, enhancing sensitivity in measurements of the Higgs boson properties, b quark tagging performance in top quark studies, and searches for beyond-Standard-Model signals including supersymmetry and long-lived particles examined by the ATLAS collaborations. Its contributions have been cited in papers by international collaborations including CERN, ATLAS Collaboration, and partner universities such as University of Sheffield and University of Melbourne, and have influenced detector design choices in experiments like CMS, LHCb, and future projects at Fermilab and KEK.

Category:ATLAS detector