Phenomenology At The CEPC:Higgs Precision Measurement And Majorana Neutrino

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 Z H 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 ?L = 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 250 Ge V and 1 Te V for different Majorana neutrino masses.We find that lepton colliders have an obvious strength in detecting Majorana neutrinos with small masses.