Realization of the low background neutrino detector Double Chooz: From the development of a high-purity liquid & gas handling concept to first neutrino data Dissertation of Patrick Pfahler TECHNISCHE UNIVERSITAT¨ MUNCHEN¨ Physik Department Lehrstuhl f¨urexperimentelle Astroteilchenphysik / E15 Univ.-Prof. Dr. Lothar Oberauer Realization of the low background neutrino detector Double Chooz: From the development of high-purity liquid- & gas handling concept to first neutrino data Dipl. Phys. (Univ.) Patrick Pfahler Vollst¨andigerAbdruck der von der Fakult¨atf¨urPhysik der Technischen Universit¨atM¨unchen zur Erlangung des akademischen Grades eines Doktors des Naturwissenschaften (Dr. rer. nat) genehmigten Dissertation. Vorsitzender: Univ.-Prof. Dr. Alejandro Ibarra Pr¨uferder Dissertation: 1. Univ.-Prof. Dr. Lothar Oberauer 2. Priv.-Doz. Dr. Andreas Ulrich Die Dissertation wurde am 3.12.2012 bei der Technischen Universit¨atM¨unchen eingereicht und durch die Fakult¨atf¨urPhysik am 17.12.2012 angenommen. 2 Contents Contents i Introduction 1 I The Neutrino Disappearance Experiment Double Chooz 5 1 Neutrino Oscillation and Flavor Mixing 6 1.1 PMNS Matrix . 6 1.2 Flavor Mixing and Neutrino Oscillations . 7 1.2.1 Survival Probability of Reactor Neutrinos . 9 1.2.2 Neutrino Masses and Mass Hierarchy . 12 2 Reactor Neutrinos 14 2.1 Neutrino Production in Nuclear Power Cores . 14 2.2 Energy Spectrum of Reactor neutrinos . 15 2.3 Neutrino Flux Approximation . 16 3 The Double Chooz Experiment 19 3.1 The Double Chooz Collaboration . 19 3.2 Experimental Site: Commercial Nuclear Power Plant in Chooz . 20 3.3 Physics Program and Experimental Concept . 21 3.4 Signal . 23 3.4.1 The Inverse Beta Decay (IBD) . 23 3.4.2 Signature of the IBD . 24 3.4.3 Expected Signal . 27 3.5 Detector Design . 29 3.5.1 Neutrino Target (NT) . 29 3.5.2 Gamma Catcher (GC) . 30 3.5.3 Buffer (BF) . 31 3.5.4 Inner Muon Veto (IV) . 31 3.5.5 Passive Steel Shielding . 31 3.5.6 Outer Muon Veto (OV) . 31 3.5.7 Detector Liquids . 32 3.5.8 Detector Readout System . 32 3.5.9 Detector Calibration System . 33 3.6 Background . 35 3.6.1 Accidental Background . 35 3.6.2 Correlated Background . 36 3.6.3 Artificial Background . 36 3.7 Neutrino Selection . 37 i CONTENTS 3.7.1 Pre-Selection Cuts for the Neutrino Search . 37 3.7.2 Neutrino Selection Cuts . 37 II Development and Production of two Detector Liquids 39 4 Hardware Installations for Detector Liquid Production 41 4.1 Liquid Storage Area (LSA) . 42 4.2 Liquid Handling System . 43 4.2.1 Pumping Stations . 46 4.2.2 Storage Tanks for Buffer and Muon Veto . 50 4.2.3 Monitoring- and Safety-Systems . 53 4.3 Gas Handling System . 56 4.3.1 Liquid Nitrogen Plant and Gas Filter Station . 58 4.3.2 High Pressure Nitrogen . 59 4.3.3 Low Pressure Nitrogen . 60 4.3.4 Low Pressure Ventilation . 60 4.4 Trunk Line System (TLS) . 61 5 Material Selection for the Detector Liquid Production 64 5.1 Organic Liquid Scintillators and Requirements for Double Chooz . 64 5.1.1 Scintillating Mechanism and Stokes Shift . 64 5.1.2 Requirements for Double Chooz . 68 5.2 Component Selection for the Muon Veto Scintillator . 69 5.2.1 Scintillating Solvent . 69 5.2.2 Non-scintillating Dilution . 71 5.2.3 Wavelength Shifter . 73 5.3 Component Selection for the Buffer Liquid . 75 5.3.1 Non-scintillating Mineral Oils . 75 5.4 Selected Components for Muon Veto Scintillator and Buffer Liquid . 77 6 Detector Liquid Production 78 6.1 Composition of Muon Veto and Buffer . 78 6.2 Preparation of the LSA . 78 6.3 Parallel Production of the Muon Veto Scintillator and Buffer Liquid . 79 6.3.1 Master Solution . 79 6.3.2 Mixing Process . 80 III Filling and Handling of the Double Chooz Far Detector 83 7 Hardware Installations for the Filling and Handling of the DC far Detector 84 7.1 Liquid Handling System . 85 7.1.1 Detector Fluid Operating System (DFOS) . 85 7.1.2 DFOS Main Operation Modes . 93 7.1.3 Expansion Tank Operating System (XTOS) . 94 7.2 Gas Handling System . 98 7.2.1 Nitrogen Supply System . 99 7.2.2 Consumers . 104 7.2.3 Ventilation System . 106 7.3 Detector Monitoring System (DMS) . 112 7.3.1 Liquid Level Monitoring Systems . 112 7.3.2 Gas Pressure Monitoring System (GPM) . 124 ii CONTENTS 8 Detector Filling 127 8.1 Preparations for Filling . 128 8.1.1 Filling Team . 128 8.1.2 Detector Flushing . 128 8.1.3 DFOS Cleaning . 129 8.2 Detector Filling . 129 8.2.1 Filling Sequence . 132 IV Performance and Results 147 9 Quality of the Produced Detector Liquids 148 9.1 Muon Veto Scintillator . 149 9.1.1 Transparency, Light Yield and Density . 149 9.1.2 Radio Purity . 151 9.2 Buffer Liquid . 151 9.2.1 Transparency, Light Yield and Density . 151 9.2.2 Radio Purity . 153 9.3 Performance of the Liquid- and Gas Handling Systems in the LSA . 153 10 Accuracy and Performance of Detector Filling and Handling 156 10.1 Detector Filling Process . 156 10.1.1 Performance of the Filling Systems . 157 10.2 Detector Handling . 162 10.2.1 Performance of XTOS . 162 10.2.2 Performance of the Gas Handling System . 165 11 Detector Performance & Results from 2012 168 11.1 Cosmogenic Muons in the Inner Muon Veto . 169 11.2 Cosmogenic Muons in the Inner Detector . 170 11.3 First Neutrino Data . 177 11.4 First Result for Θ13 .....................................180 Summary & Outlook 183 11.5 Detector Liquid Production . 186 11.6 Liquid Transfer from the Surface to the Underground Laboratory . 187 11.7 Filling of the Double Chooz Far Detector . 188 11.8 Detector Handling During Data Taking . 190 11.9 Conclusion and Outlook . 191 V Appendix 193 A Double Chooz Experiment 194 A.1 Detector Design . 194 B Surface Installations 197 B.1 Liquid Storage Area . ..