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Background Simulations and WIMP Search with Galactic Signature Dark Matter Experiments

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Background Simulations and WIMP Search with Galactic Signature Dark Matter Experiments Background Simulations and WIMP Search with Galactic Signature Dark Matter Experiments Frédéric Michel Mouton September 2017 Department of Physics and Astronomy University of Sheffield Contents 1 Introduction 15 1.1 Evidence for Dark Matter . 15 1.1.1 Galactic Rotation Curves . 16 1.1.2 Galaxy Clusters and Gravitational Lensing . 20 1.1.3 The Cosmic Microwave Background . 23 1.2 Alternatives to Dark Matter . 25 1.2.1 Modified Newtonian Dynamics . 26 1.2.2 f (R) gravity . 27 1.3 Dark Matter Candidates . 29 1.3.1 MACHOs . 29 1.3.2 Characteristics of Non-baryonic Dark Matter . 30 1.3.3 Axions . 31 1.3.4 Sterile neutrino . 33 1.3.5 Weakly Interacting Massive Particles (WIMPs) . 34 1.4 Conclusion . 38 2 Dark Matter Detection 40 2.1 Collider Searches for Dark Matter . 40 2.2 Indirect Searches . 43 2.3 Direct Detection . 44 2.3.1 Annual Modulation . 45 2.3.2 Directionality . 47 i Contents Contents 2.3.3 Spin-dependence and Nuclear Physics Effects . 49 2.4 Galactic Signature Experiments . 51 2.4.1 Scintillating Crystal Detectors . 51 2.4.2 Directional Detectors . 57 2.5 Conclusion . 64 3 Background Simulations in Annual Modulation Experiments 66 3.1 DM-Ice17 . 66 3.2 DM-Ice37 . 69 3.2.1 Background simulations for DM-Ice37 . 70 3.3 COSINE-100 . 77 3.3.1 Pulse shape discrimination in COSINE-100 . 78 3.4 Neutron background in COSINE-100 . 81 3.4.1 Neutron High Precision Models and SOURCES-4C . 83 3.5 Neutron background simulation in COSINE-100 . 85 3.5.1 (α, n) reactions and spontaneous fission . 85 3.5.2 Muon-induced Neutrons in COSINE-100 . 93 3.6 Conclusion . 98 4 Improved Detection Efficiency and WIMP search with DRIFT 100 4.1 DRIFT-IId detector technology . 101 4.2 DRIFT-IId Neutron Calibration . 106 4.2.1 252Cf calibration . 106 4.2.2 Detector simulation . 107 4.2.3 Simulation of 252Cf neutrons . 109 4.2.4 Nuclear efficiency map . 112 4.3 WIMP search analysis . 115 4.3.1 Theoretical calculation . 116 4.3.2 Data Analysis . 122 4.4 Conclusion . 127 ii Contents Contents 5 Background simulations for the DRIFT detector 130 5.1 Background from the steel vessel . 130 5.2 Radon background . 134 5.3 Background from the rock . 140 5.3.1 Environmental conditions . 141 5.3.2 New neutron shield design . 142 5.3.3 Gamma rays from the rock . 148 5.4 Conclusion . 150 6 Negative Ion TPCs as neutron detectors 152 6.1 Motivations . 153 6.2 DRIFT Unshielded Exposure . 157 6.2.1 Gamma background from the rock . 159 6.2.2 60Co Exposure . 161 6.2.3 Measurement of 238U and 232Th in the rock . 163 6.3 Measurement of the fast and thermal neutron flux at LNGS with UNDER . 166 6.4 Conclusion . 175 7 Design simulations for the CYGNUS detectors 178 7.1 Potential for neutrino discrimination . 179 7.2 Zero background feasibility in CYGNUS detectors . 184 7.2.1 CYGNUS Models . 184 7.2.2 Background simulations for the CYGNUS detectors . 186 7.3 Conclusions . 208 8 Preliminary gamma discrimination strategies 210 8.1 Quartile integration method . 210 8.2 Pulse length discrimination . 213 8.3 Conclusion . 214 iii Contents Contents 9 Conclusions and Outlook 219 Bibliography 223 iv List of Figures 1.1 Rotation curve of the galaxy ESO 2060140 observed in [9] compared to different ΛCDM simulations. From [9]. 17 1.2 Rotation velocities for a cuspy or core dark matter halo compared to data from the F568-3 galaxy. From [13]. 19 1.3 Composite images of the “Bullet Cluster” 1E0657-558 (left, from [32]) and the MACS J0025.4-1222 cluster (right, from [33]) showing the hot baryonic gas distribution in pink and the dark matter distribution in blue. 22 1.4 Planck 2015 temperature power spectrum (top) showing a good agree- ment with the ΛCDM prediction. The residuals are plotted on the bottom. From [42]. 25 1.5 Extrapolation of the gauge couplings in the standard model (left) and in SUSY (right). From [91]. 36 2.1 Feynman diagram illustrating the three strategies of dark matter de- tection. 41 2.2 Summary of ATLAS reach to new physics. 42 1 List of Figures List of Figures 2.3 Spin-independent results from IceCube showing excludable neutralino models using Minimal Supersymmetric Standard Model (MSSM). The calculation of the MSSM parameter space was done using the DarkSUSY program [113] to compute the neutralino masses. Each dot corresponds to a MSSM model. The results are compared to the XENON100 results [114] excluding all MSSM models above the gold line. From [115]. 44 2.4 Schematic view of the WIMP velocities and the effect of the Earth’s motion around the Sun. From [121]. 47 2.5 Modulation of the event rate in a directional detector at zero degree (solid line), ±18ř(dotted lines), ±54ř (dashed lines), ±90ř (dashed- dot lines) from the equatorial plane. From [123]. 48 2.6 Schematic view of the DAMA/LIBRA experiment. From [138]. 52 2.7 Spin independent limits from several experiments, including the XENON100 2012 limit [114], excluding the DAMA-allowed regions (in red). From [114]. 54 2.8 Experimental residual rate in the single event channel in DAMA. From [128]. 55 2.9 Schematics of the SABRE experiment. From [151]. 57 2.10 Distribution of nuclear recoil tracks in local altitude-azimuth coor- diantes at the Kamioka Underground Laboratory. The purple line is the track of the direction of Cygnus. From[154]. 59 2.11 Projected exclusion curve of the ADAMO detector with a 2keVeethreshold (solid black) compared to the DAMA-allowed regions (colored). The green region neglects the channeling effect in the crystal, this is in- cluded in the blue region. The red region neglects channeling but includes energy dependent quenching factors for Na and I. From [157]. 61 2.12 A charged particle track in nuclear emulsion. From [173]. 63 2 List of Figures List of Figures 3.1 Top: Muon rate in the northern hemisphere as measured by Borexino [142]. Bottom: Muon rate in the southern hemisphere measured in IceCube [180]. 67 3.2 Open view of the DM-Ice17 pressure vessels. 68 3.3 DM-Ice37 in its copper castle at Boulby. Photo courtesy of W. Pettus. 70 3.4 Simulated representation using Geant4 of the DM-Ice37 experiment at Boulby. 71 3.5 Background levels in the low energy region for DM-Ice17 (red), DM- Ice37 before (black) and after (blue) the January 2015 update. 72 3.6 Comparison between data and simulation in the high energy region for DM-Ice37. 76 3.7 Comparison between data and simulation in the low energy region for DM-Ice37. 76 3.8 The COSINE-100 crystals inside the detector. 78 3.9 Schematics of the COSINE-100 Shield. 79 3.10 Asymmetry parameter versus X1 − X2 between 4 and 5 keV. From [194]. 81 3.11 Visualisation of the geometry of the COSINE-100 detector in Geant4. 86 3.12 Neutron energy spectra in the rock for 238U and 232Th. 87 3.13 238U rock neutron flux as a function of depth. 88 3.14 Neutron energy spectra from 238U and 232Th in copper. 91 3.15 Simulated energy spectrum of muons entering the A5 room at YangYang. ....................................... 97 3.16 Simulated energy spectrum of the muon-induced neutrons entering the A5 room at YangYang. 98 4.1 The DRIFT-IId detector at Boulby. From[212]. 101 4.2 Gold-Plated Cathode Crosser event in DRIFT . 103 4.3 Time arrival distribution of negative ions in a DRIFT-like gas mixture showing the presence of minority carriers. From [216]. 104 3 List of Figures List of Figures 4.4 Graphical representation of the simulated DRIFT-IID detector in Geant4. 110 4.5 Simulated neutron energy spectrum from a 50µCi 252Cf with SOURCES- 4C......................................111 4.6 A sample of 252Cf neutron induced nuclear recoils simulated in Geant4. .......................................112 4.7 Plot of d vs NIPs for all accepted, shielded neutron events. 113 4.8 Nuclear efficiency map of the detector. From [146]. 114 4.9 Projected detection efficiency for the DRIFT-IId detector. 115 4.10 Results from 147.48 live days of shielded exposure in the JIF labora- tory at Boulby. 125 4.11 Registered signal for event 35 with a signal on the left anode wires (LA5to LA8) and the left veto (LVA and LVS). 126 4.12 Registered signal for event 3494 with a signal on the right anode wires (RA4 and RA5) and the right veto (RVA and RVS). 127 4.13 Spin-dependent WIMP-proton cross section limit at the 90% confid- ence level for this analysis (red) and other dark matter detectors. .......................................128 5.1 Simulated energy spectra of neutrons emanating from the steel due to decays from the uranium and thorium chains. 132 5.2 Energy spectrum of nuclear recoils in DRIFT due to neutrons from the steel vessel. 133 5.3 Energy spectrum of electronic recoils in DRIFT due to decays in the steel vacuum vessel. ..
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