The upgraded Pixel Detector of the ATLAS Experiment for Run2 at the Large Hadron Collider

The Pixel Detector of the ATLAS experiment has shown excellent performance during the whole Run-1 of LHC. Taking advantage of the long showdown, the detector was extracted from the experiment and brought to surface, to equip it with new service quarter panels, to repair modules and to ease installation of the Insertable B-Layer (IBL), a fourth layer of pixel detectors, installed in May 2014 between the existing Pixel Detector and a new smaller radius 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 developed. A new readout chip has been developed within 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 about less than 1 cm, the IBL detector was a challenge in terms of design and mechanical integration. An overview of the lessons learned during the IBL project will be 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 will also be presented.