(A) search for dark matter with NaI(Tl) crystal of the KIMS-NaI = KIMS-NaI 실험에서 NaI(T1) 결정을 이용한 암흑물질 탐색

다국어 초록 (Multilingual Abstract)

A number of astrophysical observations provide evidences that the dominant matter in the universe is non-baryonic dark matter. Weakly interacting massive particles (WIMPs) are strong candidates of dark matter supported by many astronomical observations as well as theoretical predictions. Numerous direct searches of WIMP dark matter have been performed by using various detection techniques.
KIMS-NaI experiment is working on the direct detection of WIMPs through weak interactions with nuclei in a NaI(Tl) crystal. KIMS-NaI collaboration installed the first NaI(Tl) crystals in Yangyang underground laboratory in 2014 and crystal R&D and data taking are underway since then. The experiment uses pulse shape discrimination (PSD) between WIMP nuclear recoil signals and backgrounds for WIMP search. This thesis describes the PSD analysis study using NaI(Tl) crystal having high light yield. The measurements of the pulse shape produced by neutrons and gamma rays in a NaI(Tl) crystal are presented and the analyses of underground data from the first two NaI(Tl) crystals based on this measurements are described. The understandings of the results from the PSD analysis are discussed and the preliminary limit using 667.16 kg days of data is described.

목차 (Table of Contents)

• Chapter 1 Dark Matter 1
• 1.1 Missing Mass in Galaxies 1
• 1.2 Evidences for Dark Matter 1
• 1.2.1 Rotation Curve of galaxy 1
• 1.2.2 Bullet Cluster 2
• 1.2.3 Gravitational Lensing 3
• 1.3 Properties 4
• 1.3.1 Standard Cosmology 4
• 1.3.2 Big Bang Nucleosynthesis 6
• 1.3.3 Cosmic Microwave Background 7
• 1.3.4 Structure Formation and Cold Dark Matter 9
• 1.4 Candidates of Dark Matter 11
• 1.4.1 Baryonic Dark Matter 11
• 1.4.2 Neutrino 12
• 1.4.3 Sterile Neutrino 12
• 1.4.4 Axions 12
• 1.4.5 Weakly Interacting Massive Particle (WIMP) 13
• Chapter 2 WIMP 14
• 2.1 Supersymmetric Dark Matter 14
• 2.1.1 Supersymmetric Model 14
• 2.1.2 Neutralino 15
• 2.2 Thermal Relic Density 16
• 2.3 Direct Detection 17
• 2.3.1 Detection of WIMP 18
• 2.3.2 Direct Detection Techniques and Experiments 26
• 2.4 Indirect Detection 29
• 2.5 Production 30
• Chapter 3 KIMS-NaI Experiment 31
• 3.1 KIMS Experiment 31
• 3.2 KIMS Detector 33
• 3.2.1 Environment of Y2L 33
• 3.2.2 Shielding 34
• 3.2.3 KIMS-CsI Detector 35
• 3.3 Electronics and Data Acquisition System 36
• 3.3.1 Overview 36
• 3.3.2 Preamplier 37
• 3.3.3 Digitizer 39
• 3.3.4 Controller 40
• 3.3.5 Event Triggering 40
• 3.3.6 Event Acquisition 41
• 3.4 Slow Monitoring 44
• 3.5 KIMS-NaI Detector 49
• 3.5.1 Scintillation Detector 49
• 3.5.2 NaI(Tl) Crystal 51
• 3.5.3 Photo Multiplier Tube 52
• 3.5.4 Congurations 55
• 3.6 Pulse Shape Discrimination in a NaI(Tl) Crystal 58
• 3.6.1 Pulse Shape Discrimination 58
• 3.6.2 Netron Calibration Setup 60
• Chapter 4 Data & Backgrounds 62
• 4.1 Data for WIMP Search 62
• 4.2 Signal in NaI(Tl) Crystal 64
• 4.2.1 Signal and Noise 64
• 4.2.2 Energy Calibration 66
• 4.2.3 Gain Variation 70
• 4.3 Event Selection 73
• 4.3.1 Single Hit and Multiple Hit Events 73
• 4.3.2 Accidental Event 74
• 4.3.3 Charge Ratio in the Signal 75
• 4.3.4 Asymmetry of the Charge Sum 77
• 4.3.5 Two events in one signal 80
• 4.3.6 Validation of Noise Rejection Cuts 83
• 4.3.7 Efficiency of Event Selection 88
• 4.4 Internal Backgrounds 93
• 4.4.1 Cosmogenic Activation 93
• 4.4.2 40K 95
• 4.4.3 238U, 232Th, 210Pb and Alpha 96
• Chapter 5 Pulse Shape Discrimination Study 99
• 5.1 Neutron Calibration Data 99
• 5.2 Underground Data 102
• 5.3 Discrimination of Nuclear Recoil Events from the Data 108
• 5.3.1 Comparison of Mean Time Distribution between Small and Full Size Crystals 108
• 5.3.2 Fitting with Electron Recoil and Nuclear Recoil 113
• 5.4 Interpretation 121
• 5.4.1 Backgrounds Interpretation 121
• 5.4.2 WIMP Interpretation 126
• Chapter 6 Conclusions 131
• Bibliography 132
• 국문 초록 137