Search for supersymmetry in the fully hadronic channel and jet calibration with the ATLAS detector at the LHC

The Standard Model of particle physics is a very precise model describing the elementary particles and their interactions. However, some issues lead physicists to search for physics beyond the Standard Model. Supersymmetry is an extension of the Standard Model providing solutions to the current issues. In this thesis, results are obtained using the data collected in 2015 and 2016 with the ATLAS detector at the LHC (CERN). The thesis is based in two parts: The first part is a performance analysis improving the energy measurement of high energy objects called "jets". They are generated by the hadronization of quarks and gluons in the detector via the strong nuclear interaction. My contribution is the last step of the the reconstruction and calibration chain and is fully based on data. The method uses the very precise measurement of the photon energy, and provides corrections to the jet energy scale. My contribution consists in set-up the method, estimate the corrections, measure the jet energy scale and evaluate the uncertainties. Corrections are at the order of 2-3\% as a function of the jet energy scale. The uncertainty of the jet energy scale is estimated to be at the order of 1\% for the three jet types. Results are now used by the ATLAS Collaboration. This method is also used to estimate the jet energy resolution. A resolution at the order of 17\%-22\% at 40 GeV depending on the jet type, and 4\% at 1 TeV is obtained with an uncertainty at the order of 10\%. The second part of the thesis corresponds to the search for supersymmetry. The signal corresponds to a pair of supersymmetric particles called squarks and gluinos and corresponds to jets and missing transverse energy in the final state. My contribution mainly corresponds to the optimisation of the selections using several simplified models of supersymmetry. Nine signal regions have been introduced in the analysis. Limits on the mass of squarks and gluinos computed during the Run 1 have been greatly improved to reach a maximal value respectively at the order of 1.6 TeV and 2 TeV.