Etalonnage du calorimètre électromagnétique d'ATLAS et recherche de la production de paires de bosons de Higgs dans l'état final bbyy avec les données de Run 2 et Run 3 collectées par le détecteur ATLAS auprès du LHC

After ten years of discovery of the Higgs boson, the LHC continues to measure the properties of the Higgs boson in greater details. The determination of the Higgs self-coupling could reveal where the new physics lies and shed light on the history of the early universe. This thesis presents the determination of the in-situ scale and resolution as well as for ATLAS electron and photon energy calibration. The resulting precision for Run 3 achieves the one for Run 2. The determination of the AtlFast3-Geant4 correction factors is also described, which is vital to maintain the achieved precision in the calibration for samples simulated with AtlFast3. A new di-Higgs production analysis in the bbyy decay channel with data collected in Run 2 and partial Run 3 period is presented. A significance of 0.8 sigma on muHH is observed, while 1.0, sigma expected. An observed 95% CL upper limit of 3.8 on muHH is set against the SM HH production hypothesis. The expected upper limit is muHH < 2.6~(3.7) against no or SM HH production hypothesis. The observed (expected) 95% CL intervals are -1.7~(-1.8) < kappa_lambda < 6.6~(6.9) and -0.5~(-0.4) < kappa_{2V} < 2.6~(2.6) respectively for klambda and kVV.