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Search for Radiative Decays of D Mesons at the Babar

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Search for Radiative Decays of D Mesons at the Babar SEARCH FOR RADIATIVE DECAYS OF D0 MESONS AT THE BABAR DETECTOR DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Joseph J. Regensburger, M.S. ***** The Ohio State University 2008 Dissertation Committee: Approved by Klaus Honscheid, Adviser Richard Kass Adviser Richard Furnstahl Graduate Program in Thomas Humanic Physics Roberto G. Rojas-Teran ABSTRACT I detail my work searching for the radiative decays of D0 mesons, e.g. D0 → φγ, within 381.7fb−1 of e+e− data collected by the BABAR detector at the PEP-II asymmetric-energy e+e− collider at SLAC from 1999-2006. Such decays are not well described under perturbative techniques typically used to estimate the frequency of decays under the Standard Model of Particle Physics (SM), and as such are valuable laboratories to investigate quantum chromodyanmics calculations (QCD). I specifically examine the Cabibbo-suppressed (CS) D0 φγ decay as well as → ∗0 search for the yet unobserved Cabibbo-favored (CF) decay, D0 K γ. I measure → the branching fractions of each mode relative to the decay D0 K−π+ and find → (D0 φγ)=(2.73 0.30 0.26) 10−5 B → ± ± × and ∗0 (D0 K γ)=(3.22 0.20 0.27) 10−4 B → ± ± × These results are preliminary and currently under review by the BABAR collaboration ahead of publication. In these expressions the first error is due to statistical sources and the second is due to systematic sources. ii ACKNOWLEDGMENTS This work would not have been possible without the expertise and advice of many people both in and out of the Physics community. I would like to thank my wife, Tammi, for her love, encouragement, and patience. This work could not have been accomplished without her emotional and intellectual support. She has been beyond generous with her time, love, and advice. I also thank my family for all of their support over these many years. I would like to thank the entire Ohio State BABAR group. Foremost I would like to thank my advisor, Dr. Klaus Honscheid, for his wisdom and generosity throughout my time at Ohio State, and Dr. Amir Rahimi for his advice and friendship over the course of this analysis. This work would have never succeeded without their input. I also extend my gratitude to Dr. Dirk Hufnagel for establishing the OSU BABAR Monte Carlo Farm and later for his time and effort training me to assume his role as the site coordinator for the Farm. On that same note, I would like to thank the OSU Physics Computer Group, in particular Tim Randles and J.D. Wear for their help in maintaining the OSU BABAR computer system. I am grateful for the extraordinary contributions of the PEP-II team in achieving the excellent luminosity and machine conditions that have made this work possible, as well as the BABAR computing group, and the BABAR Charm Analysis Working Group for their input during the process. iii I would also like to thank all of the professors and teachers who in the past have helped my development as a scientist. These include Mrs. Pam Mathis at McNicholas High School, Drs. Haowen Xi and Barry Cobb at Bowling Green State University, each of whom gave me my first exposure to academic research, and Dr. Monroe Rabin at the University of Massachusetts at Amherst. Finally I would like to thank all of my past and present colleagues. At Ohio State Don Burdette, James Morris, and Iulian Hetel have been a constant source of good company, good humor, and good collaboration. At the University of Massachusetts Don Blair, Deniz Kaya, Ozgur Yavuzcetin, Andrew Varnon, and James Heflin have long been great friends. This work is supported by the US Department of Energy. iv VITA February 26, 1975 . Born - Cincinnati, Ohio August 1993-May 1997 . Bowling Green State University, Bowling Green, OH Spetember 1999-May 2002 . .University of Massachusetts at Amherst, Amherst, MA June 2002 - .................The Ohio State University, Columbus, OH FIELD OF STUDY Major Field: Physics Studies in Experimental Particle Physics: Professor Klaus Honscheid v TABLE OF CONTENTS Page Abstract....................................... ii Acknowledgments.................................. iii Vita......................................... v ListofTables.................................... xi ListofFigures ...................................xiv Chapters: 1. StandardModel................................ 1 1.1 IntroductiontoParticlePhysics . 1 1.2 FundamentalParticles . 3 1.3 FundamentalForces............................ 3 1.3.1 Electromagneticforce. 6 1.3.2 Strongforce............................ 7 1.3.3 Weakforce ............................ 9 1.3.4 Measuring Branching Fractions . 11 vi 2. Search for Radiative Decays . 15 2.1 PreviousExperimentalStudies. 16 2.2 RadiativePenguins ............................ 16 2.2.1 Long Distance Contributions . 20 2.3 ExperimentalChallenges . 24 2.3.1 HelicityAngle........................... 28 2.3.2 Other Discriminating Observables . 30 3. The BABAR DetectorandPEP-IIStorageRing . 33 3.1 PEP-IIStorageRing ........................... 35 3.1.1 CenterofMassEnergy . 36 3.1.2 LuminosityMeasurement. 36 3.2 The BABAR Detector ........................... 40 3.2.1 Silicon Vertex Tracker . 42 3.2.2 TheDriftChamber . 44 3.2.3 Directed Internally Reflected Cherenkov Light (DIRC) Detector 44 3.2.4 Electomagnetic Calorimeter . 47 3.2.5 InstrumentedFluxReturn . 51 3.3 ParticleIdentification. 53 3.4 Monte Carlo Simulation of the BABAR Detector ............ 56 3.4.1 MCSimulation .......................... 58 3.4.2 Distributed Computing at BABAR ................ 59 4. Experimental Details and Datasets . 61 4.1 EventSelection .............................. 61 vii 4.2 MonteCarloandDataSampleSizes. 63 4.3 AdditionalEventSelection . 67 5. Experimental Search for Radiative D0 Decays ............... 80 5.1 D0 φγ Analysis ............................ 80 → 5.1.1 D0 φγ SignalShape ...................... 82 → 5.1.2 D0 φπ0 Background ...................... 86 → 5.1.3 D0 φη Background....................... 88 → 5.1.4 Remaining Background . 92 5.1.5 SummaryofSignalShapes . 95 5.1.6 FittingMethodValidation . 95 ∗0 5.2 D0 K γ Analysis ...........................101 → ∗0 5.2.1 D0 K γ SignalShape. .103 → 5.2.2 D0 K−π+π0 BackgroundShape . .105 → ∗0 5.2.3 D0 K η BackgroundShape . .106 → 5.2.4 Combinatoric Background Shape . 110 5.2.5 Additional Backgrounds . 112 5.2.6 ValidatingofFittingProcedure . .113 ∗0 5.2.7 Fitting Results While Varying (D0 K γ) .........115 B → 6. SignalShapeValidation ...........................117 6.1 SignalShapeControlSamples . .117 6.1.1 D0 K0γ Dataset........................119 → s 6.1.2 D0 K0π0 Dataset .......................121 → s ∗0 6.1.3 D0 K γ Helicity Sideband Dataset . 123 → viii 6.2 Obtaining Correction Between Data and MC . 124 6.3 Applying Corrections when Fitting Data . 129 6.3.1 Summary of Signal Shape Correction . 130 7. Results.....................................133 7.1 D0 φγ Results .............................135 → ∗0 7.2 D0 K γ Results............................137 → 7.3 ValidatingResults. .138 8. Systematics ..................................143 8.1 FittingSystematics . .144 8.1.1 Fixed PDF Systematics . 144 8.1.2 Control Sample Correction Systematics . 149 8.1.3 D0 Vη SignalShape......................151 → 8.1.4 Combinatoric Signal Shape . 152 8.2 Tracking Reconstruction and Vertexing . 153 8.3 ParticleIdentification. 154 8.3.1 D0 φγ PIDSystematic . .156 → ∗0 8.3.2 D0 K γ PIDSystematic . .156 → 8.3.3 D0 K−π+ ReferenceMode . .157 → 8.3.4 PIDSystematicSummary . .157 8.4 PhotonSystematics. .163 8.5 π0 Veto ..................................164 8.6 CutVariation ...............................166 8.7 SystematicSummary . .168 ix 9. Conclusion...................................169 Appendices: A. D0 K−π+ ReferenceMode ........................174 → A.1 EventSelection ..............................174 A.2 FittingProcedure. .176 A.3 SystematicUncertainties . .176 B. ProbabilityDistributionFunctions . 179 B.1 CrystalBallLineshape(CB) . .179 B.2 Gaussian..................................180 B.3 Chebychev Polynomials . 180 B.4 ∆M BackgroundShape . .180 Bibliography ....................................182 x LIST OF TABLES Table Page 1.1 Important properties of the fundamental Standard Model matter par- 1 ticles [1]. All of the listed particles have spin 2 . The electric charge is written in terms of the electric charge of an electron e. The upper limits displayed are at the 90% confidence level (C.L.). ... 4 1.2 SummaryofForceCarriers. 6 1.3 Inventory of Mesons Important in Radiative Analyses . 13 2.1 The current experimental status and theoretical predictions for the branching fraction of weak radiative charm decays. Statistical and systematic uncertainties are quoted for D0 φγ. The upper limits → for the remaining three modes are quoted at 90% Confidence Limit (CL).................................... 17 2.2 Short distance contributions to radiative processes . ...... 19 2.3 Summary of Theoretical Amplitude Predictions . 24 3.1 Crosssectionsforthedominantmodes . 39 3.2 LikelihoodPIDSelection . 57 4.1 MonteCarloSampleSize. 66 xi 4.2 DataSampleSize ............................. 66 4.3 Analysis D0 Vγ Cuts ......................... 77 → 4.4 D0 φγ CutEfficiencies......................... 78 → ∗0 4.5 D0 K γ CutEfficiencies ....................... 79 → 0 5.1 Correlation coefficients between D mass and cos(θH )......... 82 5.2 Final Fit Parameters for D0 φγ PDF ................ 85 → 5.3 Final Fit Parameters for D0 φπ0 PDF................ 88 → 5.4 Final Fit Parameters for D0 φη PDF................
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