Higgs Properties:Measurement Of Couplings With Standard Model Higgs Decay To Two Photons And Search For Beyond Standard Model Di-higgs Production With Final State Of WW~* And Two Photons

Since the discovery of Higgs boson by ATLAS and CMS in 2012,the measurement of the properties of the Higgs particle and the search for the Beyond Standard Model physics related to Higgs particle have been the major interests at the Large Hadron Collider(LHC).The ATLAS experiment at the LHC using the proton-proton collision,provide the opportunity to observe the Higgs boson directly.I joined the ATLAS collaboration in 2013,right after the discovery of Higgs bo-son,and I got qualified as an author of ATLAS in April 2015.This thesis introduces my work in ATLAS Collaboration during my Ph.D.I have been deeply involved in two different physics analyses with both the first and the second operational run of the LHC.The first work is on the search for both resonant and non-resonant Higgs boson pair production in the hh? WW*?? channel with 20.3 fb-1 of pp collision data at a center-of-mass energy of 8 TeV recorded with the ATLAS detector at the LHC.The result of this analysis can be either probed to the Standard Model Higgs self coupling process,or some Beyond Standard Model with heavy resonance that decays to two Standard Model Higgs.95%confidence-level upper limits on the production cross-sections are set.The observed upper limit on the non-resonant hh production mode is 11 fb,while it is expected to be 6.7 fb.The upper limits for production via narrow resonances,with the assumption gg ? H? hh?WW*?? cross section equals to 1 fb,are set as a function of the heavy Higgs boson mass,the observed limits are from 30.7 fb at 260 GeV to 6.1 fb at 500 GeV,while the expected limits are from 14.8 fb at 260 GeV to 4.4 fb at 500 GeV In addition to the upper limits,a local significance of 1.77 standard deviation is observed for both non-resonant Higgs boson pair production and resonances.No evidence is found for either resonant or non-resonant Higgs boson pair.Latter the result is combined with 3 other channels and then interpreted in the context of two simplified scenarios of the Minimal Supersymmetric Standard Model.The second work in ATLAS experiment is the Measurements of Higgs boson cou-pling properties in the di-photon decay channel with 36 fb-1 pp collision data at the center-of-mass energy of 13 TeV with the ATLAS detector.The analysis is aiming to measure the coupling properties of Higgs boson with higher precision.Results are delivered in a variety of aspects.The inclusive signal strength and individual signal strengths of the main production modes:ggH,VBF,VH,ttH are measured.The global signal strength measured is 0.99 ± 0.14,the precision is improved by a factor of 2 comparing to the ATLAS measurement at(?)=7 and 8 TeV.The simplified template cross sections measured,the framework is designed to quantify the different Higgs bo-son production processes in specific regions of phase space.The phase space is divided into 9 regions and the cross sections are reported separately.The coupling strength and tensor structure of the Higgs boson interactions are investigated using an effective La-grangian,which introduces additional CP-even and CP-odd interactions.The results are Kg = 0.76-0.14+0.17 for the coupling to gluons and k?= 1.16-0.14+0.14 for the coupling to photons.No significant new physics contributions are observed.