Contribution to the construction of the Insertable B-Layer of ATLAS for high luminosity upgrade and Research for invisible Higgs

For Run 2 of the LHC a fourth, innermost Pixel Detector layer on a smaller radius beampipe has been installed in the ATLAS Detector to add redundancy against radiation damage ofthe current Pixel Detector and to ensure a high quality tracking and b-tagging performance ofthe Inner Detector over the coming years until the High Luminosity Upgrade. State of the artcomponents have been produced and assembled onto support structures known as staves overthe last two years. In total, 20 staves have been built and qualified in a designated QualityAssurance setup at CERN of which 14 have been integrated onto the beam pipe. In the secondpart, A search for a Higgs boson produced via vector-boson fusion and decaying into invisibleparticles is discussed, using 20.3 fb−1 of proton proton collision data at the centre of massenergy of 8 TeV recorded by the ATLAS detector at the LHC. For a Higgs boson with a massof 125 GeV, assuming the Standard Model production cross section, an upper bound of 0.28is set on the branching fraction of H →invisible at 90% confidence level, where the expectedupper limit is 0.31. The results are interpreted in model of Higgs portal dark matter where thebranching fraction limit is converted into upper bounds on the dark matter nucleon scatteringcross section as a function of the dark matter particle mass, and compared to results from thedirect dark matter detection experiments.