Thesis (Ph. D.)--University of Chicago, Dept. of Physics, March 1999. / Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Texas at Austin, 1998. / Vita. Includes bibliographical references (leaves 324-331). Available also in a digital version from Dissertation Abstracts.

Thesis (M.S. in Physics)--United States Naval Postgraduate School, 1959. / "Physics and Mathematics" -t.p. Includes bibliographical references (p. 47).

Thesis--University of California, Berkeley, 1959. / "Physics and Mathematics" -t.p. Includes bibliographical references (p. 89).

Measurements of the Ƭ lepton polarization and forward-backward polarization asymmetry near the Z° resonance using the OPAL detector are described. The measurements are based on analyses of [special characters omitted] decays from a sample of 144, 810 [special characters omitted] candidates corresponding to an integrated luminosity of 151 pb-1. Assuming that the Ƭ lepton decays according to V-A theory, the average Ƭ polarization near [special characters omitted] is measured to be [special characters omitted] = (-14.10 ± 0.73 ± 0.55)% and the Ƭ polarization forward-backward asymmetry to be [special characters omitted] = (-10.55 ± 0.76 ± 0.25)%, where the first error is statistical and the second systematic. Taking into account the small effects of the photon propagator, photon-Z° interference and photonic radiative corrections, these results can be expressed in terms of the lepton neutral current asymmetry parameters: AƬ = 0.1466 ± 0.0076 ± 0.0057, Ae = 0.1464 ± 0.0108 ± 0.0036. These measurements are consistent with the hypothesis of lepton universality and combine to give [special characters omitted] = 0.1455 ± 0.0073. Within the context of the standard model this combined result corresponds to sin [special characters omitted] = 0.23172 ± 0.00092. Combining these results with those from the other OPAL neutral current measurements yields a value of sin [special characters omitted] = 0.23211 ± 0.00068. / Graduate

Resumo: O píon e o káon, como estados ligados quark-antiquark, são sistemas apropriados para o estudo de aspectos da QCD em regiões de energias baixas e intermediárias. Estes mésons vêm recebendo muita atenção, quando se usa o modelo de quark constituinte no formalismo do cone de luz para testar o regime não-perturbativo da QCD. O fator de forma eletromagnético do píon e do káon é calculado em um modelo teórico de campo pseudo-escalar com quarks constituintes, e sua estrutura é apresentada através da corrente eletromagnética extraída dos diagramas de Feynman triangulares. Utilizando tais diagramas, são obtidas as componentes "J IND.'pi'POT.+" e "J IND.'pi'POT.-"; para o píon, e as componentes "J IND.'capa'POT.+" e "J IND.'capa'POT.-"; para o káon, da corrente eletromagnética no formalismo do cone de luz. Através destas correntes, são obtidos os fatores de forma, levando-se em conta momentos transferidos baixos e intermediários. Por meio da abordagem de Feynman, além do fator de forma eletromagnético, são calculados a constante de decaimento e o raio desses mésons no formalismo do cone de luz. Uma concordância muito boa em relação aos dados experimentais é obtida. Foi mostrado que os termos de pares são essenciais para manter a covariância completa do formalismo. Este trabalho restringiu-se ao estudo dos elementos de matriz da corrente eletromagnética na camada de massa. / Abstract: The pion and kaon, as quark-antiquark bound states, are appropriate systems to study aspects of QCD at low and intermediate energy regions. The pion and kaon has indeed received much attention, being used the constituent quark model in the light-cone formalism, to check the nonperturbative regime of QCD. The electromagnetic form factor of the pion and kaon is calculated in a pseudoscalar field theoretical model whith constituent quarks, and your structure is present in terms of the eletromagnetic current extracted of the triangle diagrams. Using this diagrams, was obtained the components "J IND.'pi'POT.+" e "J IND.'pi'POT.-"; for the pion, and the "J IND.'capa'POT.+" e "J IND.'capa'POT.-"; for the kaon, of the electromagnetic current in the light-cone formalism. Following, the form factor of these mesons are obtained, considering low and intermediate transfer momenta. By means of the Feynman approach, besides of the light-cone form factor, is obtained the constat decay and charge radius for this mesons in the light-cone formalism. A fairly good agreement with experiment is obtained. It is shown that the quark-antiquark pair terms are essential for retaining full covariance. This work was restricted to the study of on-shell current matrix elements / Orientador: Lauro Tomio / Coorientador: João Pacheco B. C. de Melo / Banca: Antônio Delfino Junior / Banca: Rodolfo Alván Casana Sufientes / Mestre

No description available.

In the standard model the rare kaon decay 𝙆_𝐿 → 𝜇⁺𝜇⁻ is a highly suppressed, ``strangeness changing neutral current process'' that requires the exchange of two weak bosons with an accurately measured branching fraction 𝐵(𝙆_𝐿 → 𝜇⁺𝜇⁻) = (6.84 ∓ 0.11 ) ✕ 10⁻⁹ [1]. For this measurement to become an important short-distance test of the standard model, the competing 𝑂(𝛼²_𝙴𝙼𝐺_𝙵) two-photon contribution must be computed and removed from the total decay amplitude. While the imaginary part of this contribution can be obtained from the 𝙆_𝐿 → 𝜇⁺𝜇⁻ decay rate and the optical theorem, the real part must be computed in QCD [2]. Depending on a relative sign, a 10% calculation of the real part of the 𝑂(𝛼²_𝙴𝙼𝐺_𝙵) two-photon contribution would lead to a 6% or 17% test of the standard model. As a first step in developing a strategy for computing the two-photon contribution to the 𝙆_𝐿 → 𝜇⁺𝜇⁻ decay, we examine a simpler process 𝜋⁰ → 𝓮⁺𝓮⁻. Here no weak interaction vertex is involved and, more importantly, there is no intermediate hadronic state with a mass smaller than that of the initial pion. The sole complication arises from the presence of the two-photon intermediate state, only one of the difficulties offered by the 𝙆_𝐿 → 𝜇⁺𝜇⁻ decay. We show that the 𝜋⁰ → 𝓮⁺𝓮⁻ amplitude can be calculated with an analytic continuation method where the entire decay amplitude including the imaginary part is preserved. The real part involves non-perturbative QCD contribution and is of substantial interest, while the imaginary part of calculated amplitude can be compared with the prediction of optical theorem to demonstrate the effectiveness of this method. We obtain Re𝓐 = 18.60(1.19)(1.04) eV, Im𝓐 = 32.59(1.50)(1.65) e𝐕 and a more precise value for their ratio Re𝓐/Im𝓐 = 0.571(10)(4) from continuum extrapolation of two lattice ensembles, where 𝓐 is the decay amplitude, the error in the first parenthesis is statistical and the error in the second parenthesis is systematic. Next, we develop a computational strategy to determine the 𝙆_𝐿 → 𝛾 𝛾 decay amplitude. It involves the same hadronic matrix element as the 𝙆_𝐿 → 𝜇⁺𝜇⁻ decay as well as all the intermediate states whose energies are lower than or close to the initial kaon sate except for the |𝜋𝜋𝜇〉that is difficult to deal with. While the lattice QCD calculation is carried out in finite volume, the emitted photons are treated in infinite volume and the resulting finite-volume errors decrease exponentially in the linear size of the lattice volume. Only the 𝑪𝑷-conserving contribution to the decay is computed and we must subtract unphysical contamination resulting from single pion and eta intermediate states which grow exponentially (or fall slowly) as the time separation between the initial and final lattice operators is increased. Results from a calculation without disconnected diagrams on a 24³ ✕ 64 lattice volume with 1/𝛼 =1 Ge𝐕 and physical quark masses are presented.

No description available.

No description available.