Precision Measurement of Charged Pion and Kaon Multiplicities in E+E− Annihilation at Q = 10.52 Gev

PRECISION MEASUREMENT OF CHARGED PION AND KAON MULTIPLICITIES IN E+E− ANNIHILATION AT Q = 10.52 GEV BY MARTIN LEITGAB DISSERTATION Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Physics in the Graduate College of the University of Illinois at Urbana-Champaign, 2013 Urbana, Illinois Doctoral Committee: Professor Naomi C. Makins, Chair Associate Professor Matthias Grosse Perdekamp, Director of Research Professor John D. Stack Associate Professor Brian L. DeMarco Abstract + This thesis presents a high precision measurement of inclusive charged pion and kaon production in e e− annihilation at a center-of-mass energy of 10.52 GeV. The measurements were performed with the Belle detector at the KEKB collider at KEK in Tsukuba, Japan, on a sample of 113 106 annihilation events. × Uncertainties are kept small by applying experimental-data-driven as well as Monte Carlo-based corrections of systematic effects on measured hadron yields, such as particle misidentification, event selection and ra- diative corrections. This analysis represents the first precision measurement of multiplicities at low energy scales, far from the Z0 mass energy scale of the LEP and SLC colliders where most previous precision measurements were performed. In addition, for the first time hadron multiplicities are measured for high fractional hadron energies relative to the energy of the fragmenting parton. Comparable or higher precision than existing measurements is achieved, while still maintaining high resolution in fractional hadron energy. + Measuring high precision hadron multiplicities at low center-of-mass energy from e e− annihilation data will reduce uncertainties on fragmentation functions (FFs). These objects parametrize hadronization, the formation of hadrons from partons in the final state of scattering reactions with large momentum transfers. FFs cannot be calculated from first principles in the theory of Quantum Chromodynamics (QCD), which describes the interaction between color-charged particles, quarks and gluons. Thus FFs have to be extracted + from experimentally measured multiplicity data from e e− annihilations, lepton-nucleon scattering and proton-proton collisions in perturbative QCD (pQCD) analyses. Reducing uncertainties on FFs not only directly enhances our understanding of the process of hadronization, which is omnipresent in any reaction with hadronic final state particles. It will also allow tests of tools and concepts of QCD which currently much of pQCD calculations rely on, such as universality and factor- ization. In addition, the variation of distribution functions like FFs with energy scale predicted by QCD can be tested. Finally, more precise FFs will enable us to increase our knowledge about other non-calculable quantities in QCD like the nucleon spin structure, for example. ii Acknowledgments First and foremost, I would like to express my deep gratitude to Professor Matthias Grosse Perdekamp and the Department of Physics of the University of Illinois at Urbana-Champaign. Without their help and generous support I would have not been able to write this thesis and work on fulfilling all requirements for my degree. I would also like to thank Professor Grosse Perdekamp along with Doctor Ralf Seidl most sincerely for their excellent physics and work mentoring and patient advising. With their help I was able to complete this multi-year scientific endeavor. I would also like to thank Doctor Anselm Vossen for many helpful comments and discussions. As well, I want to use the opportunity to thank Doctor Akio Ogawa and Doctor Francesca Giordano and the members of the Belle collaboration and our group at the UIUC for helpful discussions. Likewise, thanks also to Doctor Peter Winter, David Webber and the other members of the former UIUC MuLan/ MuSun group for computing support and discussion, as well as to Doctor John Koster and Doctor Mickey Chiu. At last, I would like to express my gratitude to the staff members at KEK in Tsukuba, Japan, who made my stays for research and shift work most pleasant and enriching experiences. This work was supported by funds from NSF grant NSF-PHY-12 05 671. − − On the personal side, I am in deep gratitude of my parents and my family, for all their support and for equipping me with everything necessary to accomplish this important step in my life. The last but in no way least person to thank is my lovely fiancée Toni, whom I have shared my life with for the last two years and who always was full of support and encouragement for my work. iii Table of Contents Chapter 1 Investigating Hadronization with Experiment and Quantum Chromodynamics 1 1.1 Introduction...................................... ........ 1 1.2 Describing Hadronization with Unpolarized Fragmentation Functions.............. 3 1.3 Current Extractions of Fragmentation Functions from ExperimentalData .. .. .. .. .. 10 1.4 Relevance and Applications of Fragmentation Functions . .............. 12 1.5 The Presented Measurement- Reducing Uncertainties on FragmentationFunction . 17 1.6 Summary .......................................... ..... 20 Chapter2 TheBelleExperiment . ........ 21 2.1 IntroductiontotheKEKBAccelerator . ............ 21 2.2 TheBelleDetector ................................... ....... 22 2.3 Monte Carlo Simulation of the Belle Experiment . ......... 31 2.4 Belle Data Handling . ..... 31 Chapter 3 Experimental Data Sample for Measurement . ............ 35 3.1 MeasurementDataSample ............................. ........ 35 3.2 PerformedCorrections .............................. .......... 37 3.3 UncertaintyTreatment. .. .. .. .. .. .. .. .. .. .. .. .. .......... 37 Chapter 4 Corrections for Systematic Effects . ............. 39 4.1 Correction for Particle Misidentification . ........... 39 4.2 Correction for Sample Impurity- Non-qq¯ EventsinHadronBJ . 102 4.3 Correction for Kinematic Reconstruction/ Smearing Effects . ................105 4.4 JointCorrectionofSystematicEffects . ............117 4.5 Correction for Visible Energy Analysis Cut . ..........138 4.6 Correction for HadronBJ Data Skim Selection . ............139 4.7 Correction for ToF θ AcceptanceCut................................ 147 4.8 Correction for Initial/Final State Radiation Effects . ..............150 4.9 Normalization....................................... ...... 158 Chapter5 FinalResultsandDiscussion . ...........160 5.1 FinalMeasurementResults .. .. .. .. .. .. .. .. .. .. .. .. .........160 5.2 Analysisof HadronsfromWeakand StrongDecays . .............163 5.3 Comparison to Monte Carlo Pythia/Jetset Multiplicities . ............164 + 5.4 Comparison to Previous Experimental Results in e e− Annihilation . 167 Chapter6 SummaryandOutlook . .......169 6.1 Summary and Anticipated Impact of Analysis in Field . ..........169 6.2 Possible Improvements and Extensions of the Presented Analysis ................170 Appendix A Supplementary Material to Chapter 1 . ...........171 A.1 AKK Parton-to-Pion Fragmentation Functions vs. z .......................171 A.2 AKK Parton-to-Kaon Fragmentation Functions vs. z .......................172 iv Appendix B Supplementary Material to Chapter 4 . ...........173 B.1 Concept of Particle Identification (PID) at Belle . ............173 B.2 Likelihood Selection Cuts . ....... 176 B.3 Supplementary Material: D∗ PIDExtraction ........................... 177 B.4 Supplementary Material: Λ PID Extraction . ...........184 B.5 Supplementary Material: J/ψ PIDExtraction........................... 188 B.6 Supplementary Material: MCHadronBJ PID Extraction . .............191 B.7 Supplementary Material to PID Correction of Raw Yields . .............195 References......................................... .......196 v Chapter 1 Investigating Hadronization with Experiment and Quantum Chromodynamics 1.1 Introduction The Standard Model of Particle Physics is a generally accepted theory about fundamental particles and their interactions. Among other contributions, it contains the framework of Quantum Electrodynamics (QED). QED was motivated by fundamental physics research experiments in the late 19th and first half of the 20th century. The theory describes the interaction of charged particles via the exchange of photons in a quantized field theoretical approach. The formulation of QED as a consistent framework to describe experimental findings but also predict future measurements was largely completed at the end of the 1940s. QED is the most stringently tested physical theory developed so far. One of its predictions, the electron magnetic moment, is experimentally verified to less than one part per trillion accuracy [1]. Through the 1960s and 1970s, new experimental facilities allowed for deep insight into nucleons, which up to then were considered point-like particles. These new particle physics experiments gave evidence for and revealed an inner structure of nucleons, composed of smaller particles (e.g. Refs. [2, 3, 4]). Following the success of the QED theory, these new experimental findings were described with similar field theoretical approaches, one of which was Quantum Chromodynamics (QCD). The theory of QCD introduces a new ’color’ charge. It describes the interaction between color-charged particles, identified with quarks, q, and the mediators of the interaction, identified with gluons, g, which carry color-charge themselves. The nature of the formulation of QCD also gives rise to emergent phenomena such as parton confinement, which leads to the formation of hadrons. Since its inception, the theory has succeeded in describing

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