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Etalonnage du calorimètre électromagnétique de l’expérience ATLAS et application à la mesure des couplages du boson de (Brout-Englert-)Higgs dans le canal diphoton dans le cadre du Run 2 du LHC.

Abstract : The discovery of the Higgs boson was a major success of the run 1 of the LHC. The era of precision measurements began as any deviation from the expected Standard Model value would be a direct hint of new physics beyond the standard model. This thesis has a first focus on the calibration of the electromagnetic calorimeter of the ATLAS experiment. The final step of this calibration uses the knowledge of the line shape of the Z boson in order to correct the measured energy of electrons and photons. Recommendations for the beginning of run 2 have been given to provide calibration constants for early analyses. Run 2 calibration constants have been computed and the performances of run 1 have been reached and improved : the systematic uncertainty on the resolution constant term of the electromagnetic calorimeter, which was dominant for the Higgs boson couplings measurement at run 1, has been divided by a factor 3.The measurement of the H boson couplings consists in measuring the shape of the resonant signal over a smooth decreasing background in categories optimized for various processes, by tagging the objects produced in association with the Higgs boson. The results are based on 36 fb⁻¹ of data recorded in 2015 and 2016 at √s=13 TeV. The ratio of the measured production cross-sections of the Higgs boson over the SM expected value (µ) has been measured. No significant deviation with respect to the SM has been observed. µ = 0.99 ± 0.14. The ratios of the main production processes have also been measured: µ_{ggH} = 0.80 ± 0.18µ_{VBF} = 2.1 ± 0.66µ_{VH} = 0.7 ± 0.85µ_{ttH+tH} = 0.5 ± 0.62
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Christophe Goudet. Etalonnage du calorimètre électromagnétique de l’expérience ATLAS et application à la mesure des couplages du boson de (Brout-Englert-)Higgs dans le canal diphoton dans le cadre du Run 2 du LHC.. Quantum Physics [quant-ph]. Université Paris Saclay (COmUE), 2017. English. ⟨NNT : 2017SACLS304⟩. ⟨tel-01737255⟩

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