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Hyperon and Hyperon Resonance Properties from Charm Baryon Decays at Babar

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Hyperon and Hyperon Resonance Properties from Charm Baryon Decays at Babar SLAC-R-868 May 2007 Hyperon AND Hyperon Resonance Properties From Charm Baryon Decays At BaBar Veronique Ziegler SLAC-R-868 Prepared for the Department of Energy under contract number DE-AC02-76SF00515 Printed in the United States of America. Available from the National Technical Information Service, U.S. Department of Commerce, 5285 Port Royal Road, Springfield, VA 22161. This document, and the material and data contained therein, was developed under sponsorship of the United States Government. Neither the United States nor the Department of Energy, nor the Leland Stanford Junior University, nor their employees, nor their respective contractors, subcontractors, or their employees, makes an warranty, express or implied, or assumes any liability of responsibility for accuracy, completeness or usefulness of any information, apparatus, product or process disclosed, or represents that its use will not infringe privately owned rights. Mention of any product, its manufacturer, or suppliers shall not, nor is it intended to, imply approval, disapproval, or fitness of any particular use. A royalty-free, nonexclusive right to use and disseminate same of whatsoever, is expressly reserved to the United States and the University. HYPERON AND HYPERON RESONANCE PROPERTIES FROM CHARM BARYON DECAYS AT BABAR by Veronique Ziegler An Abstract Of a thesis submitted in partial fulfillment of the requirements for the Doctor of Philosophy degree in Physics in the Graduate College of The University of Iowa May 2007 Thesis Supervisor: Professor Usha Mallik Work supported in part by U.S. Department of Energy contract DE-AC02-76SF00515 1 ABSTRACT This thesis describes studies of hyperons and hyperon resonances produced in charm baryon decays at BABAR . 0 0 Using two-body decays of the Ξc and Ωc , it is shown, for the first time, that the spin of the Ω− is 3/2. The Ω− analysis procedures are extended to three-body final states and prop- erties of the Ξ(1690)0 are extracted from a detailed isobar model analysis of the + 0 + 0 Λc → ΛK¯ K Dalitz plot. The mass and width values of the Ξ(1690) are measured with much greater precision than attained previously. The hypothesis that the spin of the Ξ(1690) resonance is 1/2 yields an excellent description of the data, while spin + + values 3/2 and 5/2 are disfavored. The Λa0(980) decay mode of the Λc is observed for the first time. 0 + Similar techniques are then used to study Ξ(1530) production in Λc decay. The spin of the Ξ(1530) is established for the first time to be 3/2. The existence of an S-wave amplitude in the Ξ−π+ system is shown, and its interference with the Ξ(1530)0 amplitude provides the first clear demonstration of the Breit-Wigner phase motion expected for the Ξ(1530). The Ξ−π+ mass distribution in the vicinity of the Ξ(1690)0 exhibits interesting structure which may be interpreted as indicating that the Ξ(1690) has negative parity. 2 Abstract Approved: Thesis Supervisor Title and Department Date HYPERON AND HYPERON RESONANCE PROPERTIES FROM CHARM BARYON DECAYS AT BABAR by Veronique Ziegler A thesis submitted in partial fulfillment of the requirements for the Doctor of Philosophy degree in Physics in the Graduate College of The University of Iowa May 2007 Thesis Supervisor: Professor Usha Mallik Graduate College The University of Iowa Iowa City, Iowa CERTIFICATE OF APPROVAL PH.D. THESIS This is to certify that the Ph.D. thesis of Veronique Ziegler has been approved by the Examining Committee for the thesis requirement for the Doctor of Philosophy degree in Physics at the May 2007 graduation. Thesis Committee: Usha Mallik, Thesis Supervisor Paul Kleiber Craig Kletzing William Klink Helen Quinn ACKNOWLEDGEMENTS I am very much indebted to my parents for their love and support, and mostly for teaching me to never give up. I wish to thank Karl Lonngren for setting me on the path toward the comple- tion of this degree. I wish to thank my advisor, Usha Mallik, for giving me the opportunity to obtain this degree. Her support and encouragements have been most appreciated. I also wish to thank the present and past members of the BABAR group at the University of Iowa for their support. I am grateful to the members of Group B for welcoming me as part of their team. As am very happy about the prospect of working with them. I am especially grateful to Helen Quinn for sharing her time and ideas, and for being a great source of inspiration for me. Finally, I would like to express my deepest gratitude to the person who has had the largest impact on this thesis work and completion, Bill Dunwoodie. I thank him for his caring, guidance and mentoring. His sharing of ideas has truly been the foundation around which this research has grown. ii ABSTRACT This thesis describes studies of hyperons and hyperon resonances produced in charm baryon decays at BABAR . 0 0 Using two-body decays of the Ξc and Ωc , it is shown, for the first time, that the spin of the Ω− is 3/2. The Ω− analysis procedures are extended to three-body final states and prop- erties of the Ξ(1690)0 are extracted from a detailed isobar model analysis of the + 0 + 0 Λc → ΛK¯ K Dalitz plot. The mass and width values of the Ξ(1690) are measured with much greater precision than attained previously. The hypothesis that the spin of the Ξ(1690) resonance is 1/2 yields an excellent description of the data, while spin + + values 3/2 and 5/2 are disfavored. The Λa0(980) decay mode of the Λc is observed for the first time. 0 + Similar techniques are then used to study Ξ(1530) production in Λc decay. The spin of the Ξ(1530) is established for the first time to be 3/2. The existence of an S-wave amplitude in the Ξ−π+ system is shown, and its interference with the Ξ(1530)0 amplitude provides the first clear demonstration of the Breit-Wigner phase motion expected for the Ξ(1530). The Ξ−π+ mass distribution in the vicinity of the Ξ(1690)0 exhibits interesting structure which may be interpreted as indicating that the Ξ(1690) has negative parity. iii TABLE OF CONTENTS LISTOFTABLES................................. viii LISTOFFIGURES................................ x CHAPTER 1 INTRODUCTION............................. 1 1.1 The Ω−,aTriplyStrangeParticle................. 2 1.2TheQuarkModel.......................... 6 1.2.1 TheMathematicsofQuarks................ 7 1.2.2 Degeneracies......................... 8 1.2.3 LightBaryonFlavorMultiplets............... 10 1.3AdditionoftheCharmQuark................... 17 1.4CascadePhysics........................... 20 1.5 Present Status of Cascade Resonance Spectroscopy............................. 22 1.6ThesisContent............................ 25 2 PEP-II AND THE BABAR DETECTOR................. 26 2.1 Brief Description of the Collider . ................. 26 2.2OverviewoftheDetector...................... 30 2.3 Silicon Vertex Tracker (SVT) . ................. 32 2.4DriftChamber(DCH)........................ 36 2.5 Detector of Internally Reflected Cherenkov Radiation(DIRC).......................... 43 2.6ElectroMagneticCalorimeter(EMC)................ 47 2.7InstrumentedFluxReturn(IFR).................. 49 2.8TheMagnets............................. 51 2.9Electronics,TriggerandDataAcquisitionSystem......... 52 3 EVENTSELECTIONPROCEDURE.................. 56 3.1GeneralDescription......................... 56 0 − + 0 − + 3.2 Selection of Ξc →Ω K and Ωc →Ω π Events......... 58 + 0 + 3.3 Selection of Λc → ΛK¯ K Events................. 64 + − + + 3.4 Selection of Λc → Ξ π K Events................ 66 4 MEASUREMENT OF THE SPIN OF THE Ω− HYPERON..... 69 iv 4.1 Predicted Angular Distributions for CharmBaryonSpin1/2....................... 69 − 0 − + 4.2 Exclusive Ω Production in Ξc → Ω K Decay......... 72 4.2.1 TreatmentofBackground.................. 73 4.2.2 Efficiency-corrected Ω− → ΛK− Decay AngularDistribution.................... 75 4.3ResultsofFitstotheEfficiency-CorrectedData.......... 79 − 0 − + 4.4 Exclusive Ω Production in Ωc → Ω π Decay......... 82 4.5 The Use of Legendre Polynomial Moments in SpinDetermination......................... 86 4.6 The Implications of JΞc =3/2 ................... 92 4.7Summary............................... 93 0 + 5 STUDY OF THE Ξ(1690) RESONANCE PRODUCED IN Λc → ΛK¯ 0K+ DECAY.............................. 95 5.1 Extending the Ω− Spin Formalism + to Quasi-two-body Λc Decay.................... 95 5.2 Present Status of the Ξ(1690) . ................. 96 5.3Two-bodyInvariantMassProjections............... 97 5.4 Legendre Polynomial Moments for the ΛK¯ 0 System........................... 102 + 0 + 5.5 The Dalitz plot for Λc → ΛK¯ K + Evidence for a0(980) Production................. 104 5.6 Mass and Width Measurement of the Ξ(1690)0 Assuming J =1/2.......................... 106 5.6.1 Efficiency Parametrization as a Function of m(ΛKS)andcosθΛ .................... 107 5.6.2 Background Parametrization as a Function of m(ΛKS)andcosθΛ .................... 108 5.6.3 (ΛKS)MassResolutionFunctionParametrization.... 116 + 0 + 5.6.4 Isobar Model Description of the Λc → ΛK¯ K DalitzPlot.......................... 120 5.6.5 (ΛKS)MassResolutionSmearingProcedure....... 127 5.6.6 TheBinnedMaximumPoissonLikelihoodFit....... 127 5.6.7 FitResults.......................... 132 5.6.8 StudyofSystematicUncertainties............. 144 5.6.9 SummaryofSystematicUncertainties........... 148 5.7 Dalitz Plot Analyses for Ξ(1690) Spin3/2and5/2........................... 149 5.8CommentsConcerningLorentzBoostEffects........... 156 5.9Conclusions.............................. 162 v 0 + − + + 6 THE PROPERTIES OF THE Ξ(1530) FROM Λc → Ξ π K DE- CAY...................................
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