Studies Of Hâ†'γll Decays And CP Mixed Property Of The Higgs Boson In Hâ†'ZZ~*â†'4l

The Higgs boson plays an important role in our understanding of the world. Its discovery is a big triumph of the standard model. Considering that current data are consistent with the Higgs boson in the standard model, in order to find the new physics in the experiments, we have to study the precise property of the Higgs boson.In chapter1, we offer a review of the history of the Higgs mechanism and the research of the Higgs-like particle in the LHC, then the main works in this paper are discussed. In chapter2, we introduce the spontaneous symmetry breaking, Higgs mechanism and the electroweak theory.In chapter3, a brief discussion about the two-body decay of the Higgs boson in the standard model, especially the decay channel hâ†'γγ and hâ†'γZ is given. The observation and expected results in the future experiments are also discussed in this chapter.Current experiments support that the Higgs-like particle is a spin-0and parity-even particle. However, it is still possible that the new particle is a parity mixed state. In chapter4, We examine a general hZZ vertex which contains CP-even and CP-odd couplings, by studying the process hâ†'ZZ*â†'l1+l1-l2+l2-with l1, l2=e or μ, to explore the CP mixed property of the Higgs-like particle. One momentum asymmetry and two angular asymmetries have been analyzed in order to reveal the difference from different CP-couplings. Our study shows that these asymmetries could be interesting observables in the future precise experiments.In chapter5, the radiative Higgs decays hâ†'γl+l-with l=e,μ and Ï„ are an-alyzed in the standard model using mh=125GeV. Both tree and one-loop diagrams for the processes are evaluated. In addition to their decay rates and dilepton invariant mass distributions, we also discuss the forward-backward asymmetries in these modes in the new physics. Those asymmetries can directly reflect the strength of the parity breaking in the new physics, hence it is important to study them in the future exper-iments. Another Higgs rare decays hâ†'γυlÏ…l with Ï…l=Ï…e, υμ and vÏ„ are analyzed in the standard model. Our calculation shows that the inclusive width of these pro-cesses, i.e., the sum of Γ(hâ†'γυlÏ…l) for Ï…l=Ï…e, υμ,Ï…Ï„, is1.41keV, which is about15%of Γ(hâ†'γγ). Therefore, the observation of these channels in the future precise experiments may provide us some useful information on the Higgs physics both in the standard model and in its possible extensions.We summarize our results and give an outlook in chapter6.