by Li To-sing. / Bibliography: leaves 113-116 / Thesis (M.Ph.)--Chinese University of Hong Kong, 1986

The retention of quantum numbers in hadron jets was studied, and a model was constructed to infer the quantum numbers of the leading quark and antiquark in the the reaction e⁺e⁻ → qoqo → hadrons, from the quantum numbers of the final state particles. The method used involved taking a weighted average of the quantum numbers of the hadrons in the jet, with the weight assigned to each particle dependent on its kinemat-ical variables. The model was tested using the Lund Monte Carlo JETSET 7.1 at 80 GeV. It was found that in two jet events, it was possible to determine the sign of the charge of the leading partons with SO percent accuracy overall, and with greater than 94 percent accuracy in 41 percent of the events (using cuts on the weighted average to select the events). In light quark events (dd, uu, and ss), it was found that the quark jet and its flavour could be determined with about 48 percent precision and heavy quark tagging of cc and bb could be achieved in 38 and 63 percent of events respectively. In 15 percent of the light quark events, selected by consistency between the two back to back jets, successful determination of the quark jet and its flavour were obtained in 85 percent of events, with heavy quark contamination reduced to 12 and 6 percent of cc and bb events respectively. The model was also run on three jet events at 80 GeV. Although it was possible to identify one jet as a non-gluon jet (in particular the jet which subtends the largest angle with the other two jets) in 90 percent of events, it was not possible to determine which of the two remaining jets was the gluon jet. The sign of the electric charge of the non-gluon jet could be determined in 70 percent of events overall, and in 90 percent of a smaller group of 20 percent of events again using cuts on the weighted charge for the jets. The flavour of the non-gluon jet could be determined in 42 percent of events overall, and in 65 percent of a smaller group of 18 percent of events using consistency between the non-gluon jet and the other two jets, although heavy quark contamination was more significant. Finally, the accuracy with which the sign of the electric charge and flavour could be determined in two jet events at energies in the range 20 to 100 GeV was studied. It was found that as the centre of mass energy increased, the precision with which these properties could be inferred showed a marked increase. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Orientador: Adriano Antonio Natale / Banca: Juan Carlos Montero Garcia / Banca: Márcio José Menon / Resumo: Discutiremos alguns modelos fenomenológicos baseados na QCD perturbativa que tentam descreve a seção de choque total hadrônica. Falaremos sobre as principais características dos espalhamentos hadrônicos, como o crescimento da seção de choque total com a energia devido ao aumento no número de jatos, e o decrescimento da seção de choque total a baixas energias. Mostraremos a inviabilidade do tratamento perturbativo de QCD para o cálculo da seção de choque total hadrônica. Estudaremos alguns espalhamentos hadrônicos no limite de baixas energias utilizando informações não-perturbativas das propriedades do sistema, tal como o fato do gluon adquirir massa dinâmica nesta região. Averiguando propriedades e modelos que procuram descrever a seção de choque total hadrônica, obteremos idéias suficientes para propor um modelo que descreva a seção de choque total hadrônica real / Abstract: We discuss some phenomenological models based on perturbative QCD, that try to describe the total hadronic cross section. We comment on peculiarities of hadronic scattering, as the increase of cross section at high energies, as well as its decrease in low energies. Some of the problems of perturbative QCD to deal with the total cross section calculation are discussed. We discuss how non-perturbative QCD properties, as the generation of a dynamical gluon mass, can be introduced in the low energy limit of the total cross section calculation. Finally we propose a phenomenological way to modify the total hadronic cross section calculation with these non-perturbative information / Mestre

No description available.

The quark-connected part of the hadronic light-by-light scattering contribution to the muon’s anomalous magnetic moment is computed using lattice QCD with chiral fermions. We report several significant algorithmic improvements and demonstrate their effectiveness through specific calculations which show a reduction in statistical errors by more than an order of magnitude. The most realistic of these calculations is performed with a near-physical, 139 MeV pion mass on a (5.5 fm)³ spatial volume using the 48³ × 96 Iwasaki gauge ensemble of the RBC/UKQCD Collaboration.

Orientador: Marcio Jose Menon / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-04T20:13:10Z (GMT). No. of bitstreams: 1 Luna_EmersonGustavodeSouza_D.pdf: 10516190 bytes, checksum: 28a19c18006994f354667c230156c034 (MD5) Previous issue date: 2005 / Resumo: Não informado / Abstract: Not informed. / Doutorado / Física das Particulas Elementares e Campos / Doutor em Ciências