Direct Detection Of Light Dark Matter With Ionized Signal

About 27% of the energy density of the Universe consists of dark matter.It is non-luminous and rarely interacts with baryonic matter.In the past decades,different methods have been proposed to unveil the identity of the DM.However,only gravitational effects of the DM have been observed so far.The nature of DM is still elusive so that the detection of dark matter is one of the highest priorities in particle physics.In chapter1,we review the astrophysical evidence of dark matter,the relevant charateristics that can be obtained through observation and all the possible dark matter candidate.Then we introduce dark matter detection experiments and the current research of light dark matter.In capter 2,the effect of transferred momentum on SD scattering cross section are introduced based on ionization signal detection.And the interaction is about dark matter and electron.In capter 3,the Migdal effect is used to detect the direct detection of dark matter by electron recoil signal.Then we use the XENON10/100/1T experimental data to calculate the SD scattering cross section from protons and neutrons.Capter 4is the summary and discussion of this thesics and the prospect of the future research direction.The first innovation of this thesis is the introduction of spin-dependent scattering.The spin-independent interaction between dark matter and standard model particles is equivalent to an effective field.The influence of mediator particles and propagation process is ignored.In term of mediator particles,we think the scalar and vector particles are belong to spin-indepndent mediator.While the pseudoscalar and axial vector particles are belong to spin-dependent mediator.The effect of transferred momentum in spindependent scattering can not be ignored,and the momentum transferred can enhance the dark matter form factor and scattering cross section.Comparing with SI,the cross section on SD scattering can be enhanced four oeders of magnitude.In addition,we also consider all the possibilities of scalar,vector and spinor dark matter scattering with electron,and calculate the form factor and cross section of SD scattering.The second innovation of this thesis is to introduce SD scattering into Migdal effect.The Migdal effect in the scattering process of WIMPs dark matter and nucleons can generally be ignored.But when we consider the scattering of light dark matter with nucleons,the Migdal effect produces an ionization signal large enough to be observed in detectors.We calculate the scattering cross sections of dark matter with protons and neutrons under SD scattering by Migdal effect,and find that the dark matter form factor of SD scattering have suppression effect with the increase of momentum.Secondly,the ionization signal from Migdal effect is much smaller than that generated by the scattering of dark matter and electrons,which weakens the exclusion area of the scattering cross section.In addition,there are three orders of magnitude differences in the proton and neutron structure factor,this caused that there are three orders of magnitude differences in the proton and neutron scattering cross sections.