UNIVERSITY OF CALIFORNIA, IRVINE A search for proton decay via p → μ+K0 in Super Kamiokande I DISSERTATION submitted in partial satisfaction of the requirements for the degree of DOCTOR OF PHILOSOPHY in Physics by Christopher Regis Dissertation Committee: Professor David Casper, Chair Professor Hank Sobel Professor Jonas Schultz 2011 c 2011 Christopher Regis TABLE OF CONTENTS Page List Of Figures vi List Of Tables xii Acknowledgments xiv Curriculum Vitae xv Abstract Of The Dissertation xvi 1 Introduction 1 1.1TheoreticalMotivation.......................... 1 1.1.1 ConservationandSymmetries.................. 2 1.1.2 StandardModel.......................... 3 1.1.3 GrandUnifiedTheories...................... 5 1.2 Past Experimental Measurements of p → μ+K0 ............ 9 1.2.1 Soudan2 ............................. 9 1.2.2 IrvineMichiganBrookhaven(IMB)............... 9 1.2.3 Kamiokande............................ 10 1.2.4 SuperKamiokande........................ 10 1.3OverviewofExperimentalMethod................... 10 2 Detector 14 2.1CherenkovRadiation........................... 14 2.2SuperKamiokandeDetector....................... 16 2.3PhotomultiplierTube........................... 18 2.4Electronics&DataAcquisition..................... 18 2.4.1 InnerDetector........................... 18 2.4.2 OuterDetector.......................... 21 2.4.3 TriggerSystem.......................... 21 2.5WaterPurificationSystem........................ 23 2.6Calibration................................ 24 2.6.1 TimingCalibration........................ 24 2.6.2 RelativeGainCalibration.................... 25 2.6.3 AbsoluteGainCalibration.................... 27 2.6.4 WaterTransparency....................... 28 ii 2.6.5 AbsoluteEnergyCalibration................... 30 3 Simulation 38 3.1ProtonDecay............................... 38 3.1.1 FermiMomentumandNuclearBindingEnergy........ 39 3.1.2 Kaon-NucleonInteractionintheOxygenNucleus....... 40 0 → 0 3.1.3 KL KS RegenerationintheOxygenNucleus......... 41 3.2AtmosphericNeutrinoFlux....................... 42 3.3NeutrinoInteraction........................... 44 3.3.1 Elastic&Quasi-ElasticScattering................ 44 3.3.2 SingleMesonProduction..................... 46 3.3.3 DeepInelasticScattering(DIS)................. 48 3.3.4 CoherentPionProduction.................... 50 3.3.5 NuclearEffects.......................... 52 3.4DetectorSimulation............................ 54 3.4.1 Photon Propagation ....................... 54 3.4.2 Hadron Propagation ....................... 54 0 → 0 3.4.3 KL KS RegenerationinWater................. 54 4 Fully Contained Event Reduction 56 4.1Overview.................................. 56 4.2FirstReduction.............................. 56 4.3SecondReduction............................. 57 4.4ThirdReduction............................. 58 4.4.1 Through-goingMuonCut.................... 58 4.4.2 StoppingMuonCut........................ 59 4.4.3 CablePortMuons........................ 59 4.4.4 FlasherEventCut........................ 60 4.4.5 AccidentalCoincidenceCut................... 60 4.4.6 LowEnergyEventsCut..................... 61 4.5FourthReduction............................. 61 4.6FifthReduction.............................. 63 4.6.1 StoppingMuonCut........................ 63 4.6.2 InvisibleMuonCut........................ 63 4.6.3 CoincidenceMuonCut...................... 64 4.6.4 LongTailFlasherCut...................... 64 4.7FinalFullyContainedFiducialVolumeSample............. 64 5 Event Reconstruction 66 5.1StandardEventReconstruction..................... 66 5.1.1 Vertex............................... 67 5.1.2 RingCounting.......................... 71 5.1.3 ParticleIdentification....................... 73 5.1.4 MSVertexFit........................... 77 5.1.5 MomentumDetermination.................... 77 iii 5.1.6 DecayElectronSearch...................... 82 5.1.7 RingNumberCorrection..................... 83 5.2MultipleVertexEventReconstruction.................. 84 5.2.1 StandardReconstructionWithoutTimingCuts........ 85 5.2.2 PMTMaskingRegion...................... 86 5.2.3 Primary μ-candidateReconstruction.............. 86 5.2.4 RemainingParticleReconstruction............... 92 6 Overview of the p → μ+K0 search 95 6.1DataSet.................................. 95 6.2 Strategy of the Combined p → μ+K0 Search.............. 96 0 → 0 0 7Searchfor“KS π π ”99 7.1EventSelection.............................. 99 7.2SK-IDataSideband........................... 106 7.3SK-IDataEventRatevs.EventSelection............... 111 7.4BreakdownofRemainingBackground.................. 118 7.5SK-IDataCandidates.......................... 120 0 → 0 0 7.6 Total Systematic Error of “KS π π ”Search............ 122 0 → + − 8Searchfor“KS π π Method #1” 124 8.1EventSelection.............................. 124 8.2SK-IDataSideband........................... 130 8.3SK-IDataEventRatevs.EventSelection............... 133 8.4BreakdownofRemainingBackground.................. 139 8.5SK-IDataCandidates.......................... 140 0 → + − 8.6 Total Systematic Error of “KS π π Method#1”Search..... 148 0 → + − 9Searchfor“KS π π Method #2” 150 9.1EventSelection.............................. 150 9.2SK-IDataSideband........................... 154 9.3SK-IDataEventRatevs.EventSelection............... 157 9.4BreakdownofRemainingBackground.................. 162 0 → + − 9.5 Total Systematic Error of “KS π π Method#2”Search..... 163 0 10 Search for “KL” 165 10.1EventSelection.............................. 165 10.2SK-IDataSideband........................... 175 10.3SK-IDataEventRatevs.EventSelection............... 180 10.4BreakdownofRemainingBackground.................. 188 10.5SK-IDataCandidates.......................... 189 0 10.6 Total Systematic Error of “KL”Search................. 191 11 Results 193 12 Comparison With Previous SK p → μ+K0 Search 196 iv 13 Future Prospects 202 14 Conclusion 204 Appendices 205 A SystematicErrors............................. 205 A.1 DataSet.............................. 205 A.2 SourcesofError.......................... 206 Bibliography 217 v LIST OF FIGURES Page 1.1 FeynmandiagramsofSU(5)GUTgaugebosons............ 7 1.2 Feynman diagram of Higgsino exchange from d=5 operator in the SUSYGUTLagrangian......................... 9 1.3 Feynman diagram of p → νK¯ + decay.................. 9 2.1 RelativeCherenkovlightspectruminpurewater........... 15 2.2 TheSuperKamiokandedetector.................... 17 2.3 The50cmPMT............................. 19 2.4 Thequantumefficiencyofthe50cmPMT............... 19 2.5 Thetransittimespreadofthe50cmPMT............... 20 2.6 SchematicoftheSKIDDAQsystem.................. 22 2.7 SchematicoftheSKwaterpurificationsystem............. 24 2.8 Timingcalibrationsystem........................ 25 2.9 RelativegaincalibrationsystemusingXelamp............ 26 2.10 AbsolutegaincalibrationusingaNi+Cfsource............ 27 2.11 Waterattenuationlengthmeasurementsystem............ 28 2.12 Distributionofcorrectedp.e.vs.photontravellength......... 30 2.13 Momentumdistributionfordecayelectrons.............. 31 2.14 Invariant mass distribution of neutrino induced π0 events....... 32 2.15 Distribution of reconstructed momentum from observed charge vs. reconstructed Cherenkov opening angle for cosmic ray stopping μ.. 33 2.16 Ratio of the muon momentum from observed p.e. to momentum from openingangleasafunctionofthemomentum............. 34 2.17 The ratio of momentum/range as a function of range for cosmic ray stopping μ................................. 35 2.18 Timevariationofenergyscalecalibration............... 36 2.19 The non-uniformity of the detector gain as a function of zenith angle. 37 2.20 Summaryoftheabsoluteenergyscalecalibration........... 37 3.1 Nucleon momentum distributions of 12C................ 39 3.2 Invariant mass of μ+K0 in the p → μ+K0 MC simulation in water. 40 3.3 Primary cosmic ray flux measurements compared with the model used intheHondafluxcalculation...................... 43 3.4 ThepredictedatmosphericneutrinofluxesattheSKsite....... 43 3.5 Quasi-elastic scattering cross-sections of ν andν ¯............ 46 vi 3.6 Cross-sections for charged current single pion productions of νμ... 48 3.7 Cross-sections for charged current νμ andν ¯μ interactions....... 50 3.8 The cross-sections of coherent pion productions off the carbon nucleus forCCandNCinteractions....................... 52 3.9 Cross-sections of π+-16O scattering as a function of π+ momentum. 53 3.10 Wavelength dependence of photon attenuation coefficients used in MCsimulation.............................. 55 5.1 The reconstructed-true muon momentum of three control samples describedinthetext........................... 81 5.2 Performance of the initial vertex fitting of the μ-candidate for p → + 0 μ KL MC................................. 88 5.3 The ΔV distribution of the initial μ-candidate vertex for atmospheric neutrinoMC............................... 88 → + 0 5.4 The PID likelihood of the true primary muon for p μ KL MC. 89 5.5 Performance of the MS vertex fitting of the μ-candidate for p → + 0 μ KL MC................................. 90 5.6 The ΔV distribution of the μ-candidate MS vertex for atmospheric neutrinoMC............................... 91 5.7 The reconstructed-true momentum of the true primary muon for p → + 0 μ KL MC................................. 91 5.8 Performance of the remaining particle vertex fitting of the μ-candidate → + 0 for p μ KL MC............................ 93 5.9 The ΔV− distribution for the remaining particle vertex of the atmo- sphericneutrinoMC........................... 94 6.1 The p → μ+K0 combinedsearchalgorithm..............