The upgraded Pixel Detector of the ATLAS Experiment for Run-II at the Large Hadron Collider

The Pixel Detector of the ATLAS experiment has shown excellent performance during the whole Run-1 of the LHC. Taking advantage of the detector development period 2013 – 2014, the detector was extracted from the experiment and brought to surface to equip it with new service panels and to repair modules furthermore this helped with the installation of the Insertable B-Layer (IBL), fourth layer of pixel, installed in between the existing Pixel Detector and a new beam-pipe at a radius of 3.3 cm. To cope with the high radiation and increased pixel occupancy due to the proximity to the interaction point, two different silicon sensor technologies (planar and 3D) have been used. A new readout chip has been designed with CMOS 130nm technology with larger area, smaller pixel size and faster readout capability. Dedicated design features in combination with a new composite material were considered and used in order to reduce the material budget of the support structure while keeping the optimal thermo-mechanical performance. Due to the limited radial space, the IBL detector was a challenge in terms of design and mechanical integration. An overview of the lessons learned during the IBL project is presented, focusing on the challenges and highlighting the issues met during the production, integration, installation and commissioning phases of the detector. Early performance tests using cosmic and beam data are also presented.