【作者】 孙毅；

【导师】 高道能；

【作者基本信息】 中国科学技术大学 ， 理论物理， 2014， 博士

【摘要】 Higgs玻色子在我们理解物质的质量起源中起到了非常重要的作用。在实验上发现该粒子是标准模型的巨大成功。考虑到目前的实验数据与标准模型的预言在误差范围内是吻合的,为了在实验上发现新物理的迹象,我们必须对Higgs粒子做精确的研究。在第1章,我们简单地介绍一下Higgs机制的历史以及LHC上Higgs粒子研究的现状,然后引出本文的主要工作。在第2章中我们介绍一些背景知识,包括自发对称性破缺,Higgs机制以及电弱统一理论。在第3章,我们介绍标准模型中Higgs玻色子主要的两体衰变道,尤其是h→γγ和h→γZ衰变道并介绍了目前这些衰变道在LHC上的观测结果以及未来的研究预期。目前的实验倾向于支持Higgs-like粒子是一个零自旋偶宇称粒子,但Higgs-like粒子是一个宇称混合态的可能性并不能被排除。在第4章中通过分析一个包含奇宇称和偶宇称的一般的hZZ耦合顶角以及h-→ZZ*→l1+l1-l2+l2-(l1和l2可以是电子或μ子)衰变过程,我们研究了该过程中的一个high-low momentum asymmetry和两个angular asymmetries。这些不对称性能够揭示hZZ耦合中各种宇称耦合的差异并进而得到Higgs-like粒子的宇称混合信息。我们的研究显示在未来高精度的实验上这些不对称性是很有趣的可观测量。在第5章,我们讨论了标准模型中Higgs粒子的稀有衰变道h→γl+l-,其中l=e,μ和τ。计算中包括了树图和圈图的贡献。除了该过程的衰变宽度和双轻子不变质量谱外,我们还讨论了在新物理框架下该衰变过程可能出现的forward-backward asymmetries。我们发现该不对称性能够直接反映新物理中宇称破坏的程度,因此在实验上有着重要意义。另一个稀有衰变道h→γυlυl(其中Vl可以是Ve,Vμ和Vτ)在标准模型中的行为也在本文中做了讨论。我们的计算表明该过程的总宽度是1.41keV,约占双光子衰变道的15%。因此,在将来的高精度实验中,这些衰变道的测量将会为我们提供关于标准模型和新物理的丰富信息。在第6章,我们给出总结与展望。更多还原

【Abstract】 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 h→γγ and h→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 h→ZZ*→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 h→γl+l-with l=e,μ and τ 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 h→γυlυl with υl=υe, υμ and vτ are analyzed in the standard model. Our calculation shows that the inclusive width of these pro-cesses, i.e., the sum of Γ(h→γυlυl) for υl=υe, υμ,υτ, is1.41keV, which is about15%of Γ(h→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.更多还原