LHC上Higgs粒子的发现是近年来高能物理发展中的里程碑事件。一方面，Higgs粒子补上了标准模型的最后一块，标志着旧时代的结束；另一方面，它又与新物理有紧密的联系，可以说是新时代的开端。尽管标准模型可以描述几乎所有的实验观测，但我们知道它不是一个最终的理论。我们还没有完全理解电弱对称破缺的真实过程，Higgs场势能函数的形式还有待确定，此外Planck能标和电弱能标之间的巨大差距也需要一个合理的解释。一个0自旋的Higgs 玻色子的发现使得这些问题变得更加尖锐，对这些问题的解答也必然会涉及到超出标准模型的新物理。Higgs物理的精密测量是探索新物理的重要手段，而一个作为Higgs工厂而运行的轻子对撞机无疑是这项任务的最佳选择。本文在回顾了标准模型的相关内容和问题之后，介绍了下一代轻子对撞机CEPC的设计方案和性能表现。CEPC的首要目标就是Higgs物理的精密测量。受限于探测器的分辨率，CEPC无法直接测量Higgs粒子的衰变总宽度，需要依靠特定衰变道的截面和分支比来计算总宽度。而W fusion过程正是其中很重要的一个输入量。W fusion过程截面的测量会受到ZH道的影响。这种影响有两部分组成，一部分来自于两个道之间的量子干涉效应，一部分是在耦合参数拟合过程中的相互影响。本文分析了W fusion过程的测量中所受到的这种影响。如果忽略了ZH道的影响，W fusion过程测量结果的精度和期望值都会出现很大的偏差。除了在Higgs物理精密测量方面的潜力，CEPC也是一个研究中微子质量问题的有效工具。如果中微子是Majorana费米子，那么它将导致ΔL=2的轻子数破坏过程。本文讨论了正负电子对撞机上Majorana中微子独有的这种信号的显著度。本文采用模型无关的唯象分析方法，计算了运行能量分别为 250GeV 和 1TeV 的正负电子对撞机对不同质量的Majorana中微子的探测灵敏度。我们发现，轻子对撞机在低质量的Majorana中微子探测方面具有比较明显的优势。
The discovery of a Higgs boson at the LHC is a milestone in the development of high energy physics in recent years. Although the Standard Model (SM) can describe almost all experimental observations, we know it is not a complete theory. We have not fully understood the nature of electroweak phase transition, and the form of the Higgs potential has yet to be determined. In addition, the huge gap between the Planck scale and the weak scale also needs a reasonable explanation. The discovery of a spin 0 Higgs boson only sharpens these problems. Higgs physics precision measurement is an important means of exploring new physics, and a lepton collider operating as a Higgs factory is a natural candidate for this task. After reviewing the basic construct and relevant problems of the SM, we introduce the design and performance of the CEPC, whose primary goal is the precision measurement of Higgs physics. The W fusion process is an important input at the CEPC for calculating the Higgs boson width, while its measurement will be affected by the ZH channel. This effect consists of two parts, one is from the quantum interference effect between the two channels, and the other is their interplay during the coupling fitting procedure. We analyzes the size of the effect, which if ignored, would cause large deviations in both the precision and expected value of the W fusion measurement.CEPC is also an excellent tool for studying neutrino mass problems. If neutrinos are Majorana fermions, it would lead to lepton number violation processes with ΔL=2. We study the significance of this signal unique to Majorana neutrinos at lepton colliders. In this thesis, a model-independent phenomenological approach is employed to calculate the sensitivity of lepton colliders operating at 250GeV and 1TeV for different Majorana neutrino masses. We find that lepton colliders have an obvious strength in detecting Majorana neutrinos with small masses.
