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The Search for Rare Non-Hadronic B-Meson Decays with Final-State Neutrinos Using the BABAR Detector

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The Search for Rare Non-Hadronic B-Meson Decays with Final-State Neutrinos Using the BABAR Detector The Search for Rare Non-hadronic B-meson Decays with Final-state Neutrinos using the BABAR Detector Dana Lindemann Doctor of Philosophy Physics Department McGill University Montr´eal, Qu´ebec April 2012 A thesis submitted to McGill University in partial fulfillment of the requirements of the degree of Doctor of Philosophy. c Dana Lindemann, 2012 ACKNOWLEDGEMENTS I am grateful to the members of the BABAR Collaboration and the PEP-II staff for their dedicated years of work and service to provide the luminosity and detector quality that enables me to analyse a wealth of data in these analyses. I also thank my supervisor, Professor Steven Robertson, for all of his excellent guidance, knowledge, and advice with which he has provided me over the course of my schooling. In addition, I am grateful to Paul Mercure, for his knowledgeable and frequent computing help; Malachi Schram, for the many fun and helpful conversations on our analyses; Miika Klemetti, whose code was an invaluable reference for me when I first began my analyses; and Racha Cheaib, with whom it has been a pleasure to collaborate and share an office. I also thank the members of the Leptonic analysis working group, not only for developing and improving the hadronic-tag reconstruction algorithm, but also for all their feedback on my analyses — particularly Steven Sekula, Guglielmo DeNardo, Silke Nelson, Aidan Randle-Conde, and Owen Long. Thank you to my two review committees, consisting of Ingrid Ofte, Elisabetta Baracchini, David Hilton, Kevin Flood, and Francesca De Mori, for the amount of work and time they spent on reviewing and improving my results and publication. I am also grateful to my many colleagues in the SuperB Collaboration, who contributed to my appreciation of the considerations, challenges, and excitement involved in designing a B Factory. Finally, I thank Marc-Andr´eGingras, for all of his support, patience, and kindness during my schooling. Also, I thank my parents, Mark and Vivian Lindemann, and my brother, Erik Lindemann, for their lifetime of love, encouragement, and confidence in all of my endeavours, including this one. ii ABSTRACT This thesis presents the searches for two rare B meson decays: the radiative leptonic decay B+ ℓ+ν γ (ℓ = e, µ) and the flavor-changing neutral current B → ℓ → K(∗)νν. These searches use the full dataset collected by the BABAR experiment, which corresponds to almost 500 million BB pairs. After fully reconstructing the hadronic decay of one of the B mesons in Υ (4S) BB decays, evidence of B+ ℓ+ν γ or → → ℓ B K(∗)νν is looked for in the rest of the event. No significant evidence of either → signal decay is observed. Model-independent branching-fraction upper limits are set at (B+ e+ν γ) < 17 10−6, (B+ µ+ν γ) < 24 10−6, and (B+ ℓ+ν γ) < B → e × B → µ × B → ℓ 15.6 10−6, all at the 90% confidence level. These are currently the most stringent × published upper limits for B+ ℓ+ν γ. In addition, branching-fraction upper limits → ℓ are set at (B+ K+νν) < 3.7 10−5, (B0 K0νν) < 8.0 10−5, (B+ B → × B → × B → K∗+νν) < 11.5 10−5, and (B0 K∗0νν) < 9.2 10−5, all at the 90% confidence × B → × level. For additional sensitivity to New Physics contributions, partial B K(∗)νν → branching-fraction upper limits are also determined over the full kinematic range. iii ABREG´ E´ Cette th`ese pr´esente l’´etude de deux d´esint´egrations rares de m´esons B: la d´esint´egration radiative leptonique B+ ℓ+ν γ (ℓ = e, µ) et le courant neutre → ℓ qui change la saveur B K(∗)νν. Ces ´etudes utilisent l’ensemble des donn´ees re- → cueuillies par l’exp´erience BABAR ce qui correspond `apr`es de 500 millions paires BB. Apr`es la reconstruction totale de la d´esint´egration hadronique de l’un des m´esons B dans la d´esint´egration Υ (4S) BB, la manifestation de B+ ℓ+ν γ → → ℓ ou B K(∗)νν est recherch´edans le reste de l’´ev´enement. Aucune preuve significa- → tive de la d´esint´egration du signal n’a ´et´eobserv´ee. Les limites sup´erieures du rapport d’embranchement ind´ependantes du mod`ele sont ´evalu´ees `a (B+ e+ν γ) < 17 B → e × 10−6, (B+ µ+ν γ) < 24 10−6, et (B+ ℓ+ν γ) < 15, 6 10−6, `aun niveau de B → µ × B → ℓ × confiance de 90%. Ce sont actuellement les limites sup´erieures les plus strictes publi´es pour B+ ℓ+ν γ. De plus, les limites sup´erieure du rapport d’embranchement → ℓ sont ´evalu´ees `a (B+ K+νν) < 3, 7 10−5, (B0 K0νν) < 8, 0 10−5, B → × B → × (B+ K∗+νν) < 11, 5 10−5, et (B0 K∗0νν) < 9, 2 10−5, `aun niveau B → × B → × de confiance de 90%. Pour demeurer r´eceptives aux contributions de la nouvelle physique, les limites sup´erieures du rapport d’embranchement partiel de B K(∗)νν → sont d´etermin´es dans le spectre cin´ematique complet. iv TABLE OF CONTENTS ACKNOWLEDGEMENTS ............................ ii ABSTRACT .................................... iii ABREG´ E......................................´ iv LISTOFTABLES ................................. viii LISTOFFIGURES ................................ x 1 Introduction.................................. 1 2 AnalysisMotivations ............................. 4 2.1 StandardModelofParticlePhysics . 4 2.1.1 Overview............................ 4 2.1.2 FundamentalParticles in theStandardModel . 5 2.1.3 ElectromagneticInteraction. 7 2.1.4 StrongInteractionandHadrons . 7 2.1.5 The Higgs Mechanism and the Weak Interaction . 8 2.1.6 CKMMatrixandCPViolation . 10 2.1.7 Flavor-ChangingNeutralCurrents . 13 2.1.8 EffectiveFieldTheories . 14 2.1.9 BeyondtheStandardModel . 16 2.2 OverviewofExperimentalAnalyses . 19 + + 2.3 B ℓ νℓγ intheStandardModel . 21 2.4 B →K(∗)νν intheStandardModelandBeyond . 26 → 3 ExperimentalEnvironment.......................... 33 3.1 The BABAR Experiment........................ 33 3.2 ThePEP-IIAcceleratorandCollider . 34 3.3 The BABAR detector.......................... 36 3.3.1 TheSiliconVertexTracker(SVT) . 39 3.3.2 TheDriftChamber(DCH) . 40 3.3.3 The Detector of Internally Reflected Cherenkov light (DIRC) 42 3.3.4 TheElectromagneticCalorimeter(EMC) . 45 3.3.5 TheInstrumentedFluxReturn(IFR) . 47 3.4 EventReconstruction......................... 49 3.4.1 ChargedParticleTracking . 49 3.4.2 ChargedParticleIdentification . 50 v 3.4.3 NeutralClusterReconstruction. 51 3.5 BABAR DatasetandSimulation. 52 3.5.1 The BABAR Dataset ...................... 52 3.5.2 EventSimulation ....................... 53 3.5.3 OptimizationandBlinding . 57 3.5.4 RemarksAboutPlots . 59 4 Hadronic-Tag B-MesonSelection ...................... 60 4.1 Hadronic-TagReconstruction . 60 4.1.1 ComparisonwithOtherAnalyses . 63 4.2 Energy-SubstitutedMass. 65 4.3 ContinuumLikelihoodandMissingMomentum . 66 4.4 Purity ................................. 71 5 B+ ℓ+ν γ AnalysisProcedure.. .. .. ... .. .. .. .. .. ... 75 → ℓ 5.1 SignalSelection ............................ 75 5.1.1 SignalLeptonandPhotonSelection . 75 5.1.2 EventTopologicalSelection. 77 + 0 + 5.1.3 Peaking B Xuℓ νℓ BackgroundSuppression . 79 5.1.4 AdditionalClusterEnergy→ . 83 5.2 SignalKinematics........................... 85 5.2.1 Model-DependentKinematicSelection . 85 5.3 PeakingBackgroundEstimation . 88 5.3.1 PeakingBackgroundMonteCarlo . 89 5.3.2 PeakingBackgroundForm-Factors . 92 + + 5.4 B ℓ νℓγ SelectionOptimization . 95 5.5 CombinatoricBackgroundEstimation→ . 95 5.6 SystematicUncertainties . 99 5.6.1 Branching Fraction and Form-Factor Uncertainties . .. 99 2 5.6.2 mν Uncertainties........................ 100 5.6.3 CombinatoricRatioUncertainty . 101 5.6.4 AdditionalUncertainties . 102 5.6.5 ControlSample ........................ 103 5.7 BranchingFractionExtraction . 104 + + 5.8 B ℓ νℓγ Results ......................... 107 5.8.1→ Model-DependentResults. 110 5.8.2 High Eγ BranchingFraction . 112 6 B K(∗)νν AnalysisProcedure. 116 → 6.1 SignalSelection ............................ 116 6.1.1 Signal K(∗) Reconstruction . 116 6.1.2 AdditionalClusterEnergy . 120 6.1.3 MissingEnergy ........................ 123 6.2 B K(∗)νν SignalKinematics . 123 → vi 6.2.1 KinematicModeling. 123 6.2.2 KinematicSelection . 126 6.3 PeakingBackgroundEstimation . 129 6.4 B K(∗)νν SelectionOptimization . 131 6.5 CombinatoricBackgroundEstimation→ . 132 6.6 B K(∗)νν SystematicStudies . 134 6.6.1→ BackgroundEstimateUncertainties . 134 6.6.2 Control Sample and Eextra Uncertainty . 135 6.6.3 sB Uncertainty......................... 138 6.6.4 AdditionalUncertainties . 140 6.7 BranchingFractionExtraction . 142 6.7.1 SignalCross-Feed . 142 6.8 B K(∗)νν Results ......................... 143 → 6.8.1 PartialBranchingFractionResults. 146 7 Conclusions .................................. 151 Appendix:AuthorDeclaration . 154 References...................................... 155 vii LIST OF TABLES Table page 2–1 Summary of the measured properties of the SM fermions. ..... 6 2–2 Summary of the measured properties of the SM bosons. .... 6 2–3 Summary of the mesons most relevant to this thesis. ..... 9 + + 2–4 Previously measured B ℓ νℓγ branching-fraction upper limits at the 90% confidence level,→ not including the published results described inthisthesis. .............................. 20 2–5 Previously measured B K(∗)νν branching-fraction upper limits at the90%confidencelevel.→ . 21 3–1 Production cross-sections (σ) in e+e− annihilation at a CM energy of 10.58GeV. ................................ 53 3–2 The data luminosity and estimated number of BB pairs (NBB) within each run of BABAR data-taking. .................... 53 3–3 The cross-sections and numbers of generated events in the generic + + background MC samples that are used in the B ℓ νℓγ and B K(∗)νν analyses...........................→ 55 → 3–4 The number of
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