Precision measurement of charged pion and kaon multiplicities in e+e− annihilation at Q = 10.52 GeV

hadron production;electron-positron annihilation;hadron multiplicities;precision measurement;Quantum Chromodynamics;nuclear physics

Leitgab, Martin

关键词: hadron production;    electron-positron annihilation;    hadron multiplicities;    precision measurement;    Quantum Chromodynamics;    nuclear physics;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/44363/Martin_Leitgab.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

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 million 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 radiative 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 factorization. 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.