Recherche d'une nouvelle particule dans le canal HH->yybb avec le détecteur ATLAS

The Standard Model is one of the most proven theory. The discovery of the Higgs boson, by the ATLAS and CMS collaborations in 2012, is its best achievement. However, some discrepancies exist between the theoretical prediction and the experimental measurements. Some models try to explain such differences and predict phenomena that are not predicted by the Standard Model. Such phenomena can appear in the not yet measured Higgs boson pair production via the trilinear coupling. However its low probability makes it unlikely to be measured with the current amount of data. It will be one of the projects of the HL-LHC. Some models also predict the presence of a new particle. Such presence will enhance the Higgs boson pair production via a resonance production. The search for this particle will either lead to the discovery of the particle or in an experimental constraint of the beyond Standard Model theories. The final state containing two photons and two b quarks suffers from a low rate. But this final state is chosen due to its high resolution and due to the good quality of the photon reconstruction, identification and isolation tools.\\ Many studies are conducted in order to improve those tools. Here we test a correction method that aims to reduce the pile-up impact over the photon identification. Such correction will be needed for the HL-LHC, the next generation of the LHC, where the luminosity will be higher. The goal is to maintain the efficiency that we currently have at the very least. The estimation of the uncertainty of the shower shapes lateral modelization on the photons energy is also studied. \\ The study of the search of this final state using the whole Run 2 data is presented. No excess was observed in the data, hence limits on the cross section over the mass of the resonance are computed for a mass of the resonance from 250 GeV to 1 TeV. Those new computed limits are improved in comparison to the previous analysis done in 2016 in the middle of Run 2. The final state containing two photons and two b quarks is the most sensitive to the lower masses, in the 250 to 350 GeV region. The result will be combined with results from searches with other final states and will then be interpreted in order to constrain the theoretical model.