Neste trabalho buscamos explorar os efeitos do campo magnético, criado em colisões de íons pesados não-centrais, em estados ligados. Motivados pelo caso do átomo de hidrogênio, onde a presença do campo magnético deixa o estado mais ligado,estudamos o caso dos mésons B e D. Inicialmente trabalhamos com a equação de Schrödinger e utilizamos o modelo de potencial de Cornell que faz uma boa descrição da espectroscopoia de mésons pesados. Em seguida, utilizando as regras de soma da QCD, procuramos introduzir o efeito do campo magnético no cálculo da massa de mésons. O ponto de partida foi substituir o propagador livre dos quarks pelo propagador de Schwinger, que corresponde ao propagador de um férmion na presença de um campo magnético externo e constante. Tratamos do limite de campo fraco, onde eB « m2 « M2 e o de campo muito forte, onde eB » M2, sendo m a massa do quark leve e M a massa do quark pesado. Em todos os casos observamos uma tendência da queda na massa do méson devido ao campo magnético. Esta mudança poderia ter diversas implicações fenomenológicas, como por exemplo na taxa de produção do quarkonium, que ilustramos utilizando o modelo de evaporação de cor. / At the present work, we explore the effects of the magnetic field on bound states. Such field is generated by non-central heavy ion collisions. Since the presence of magnetic field results in more deeply bounded states for the hydrogen, we will analyze the cases of mesons B and D. Initially we investigate the Cornell potential in the Schrödinger equation, which is usually a good description of the spectroscopy of heavy mesons. Next, as we examine the model using QCD sum rules, we tried to introduce the magnetic field and its consequences in the meson mass calculation. The starting point was to substitute the free propagator of quarks by the Schwinger propagator, which corresponds to the propagator of a fermion in the presence of an external constant magnetic field. We explored the weak field limit, where eB « m2 « M2 and of very strong fields, where eB » M2, for m being the mass of the light quark and M the mass of the heavy quark. In all cases we observed a trend of decreased meson mass due to the magnetic field. These variations could have many phenomenological implications; for instance, the production rates of quarkonium, illustrated by the method of color evaporation.

This thesis presents precision measurements and phenomenological studies of quark and gluon radiation in top-antitop and Z+jets final states. A measurement of top-antitop production with a veto on additional jet activity is performed using 2.1 inverse femtobarn of proton-proton collision data with a centre-of-mass energy of 7 TeV, collected by the ATLAS detector. Jet veto efficiency measurements are performed in several regions of rapidity and corrected for the effects of finite detector resolution and acceptance. A total experimental uncertainty of less than 5% is achieved in all distributions. Two phenomenological studies are performed on the additional quark and gluon radiation produced in association with boosted top-antitop systems. In the first study it is shown how a measurement of the jet veto efficiency can be used to identify the colour of a TeV-scale resonance decaying to top-antitop. The second follow-up study describes how the performance of several top-tagging algorithms is affected by the colour structure of an event. Measurements of the electroweak production of dijets in association with a Z-boson and distributions sensitive to vector boson fusion are performed using 20.3 inverse femtobarn of proton-ptoron collision data collected by ATLAS at 8 TeV. Detector-corrected differential cross sections, and distributions sensitive to radiation produced in addition to the Zjj system, are measured in five fiducial regions with varying sensitivity to the electroweak component of the Zjj cross section. Data are compared to MC predictions and are in reasonable agreement in the majority of cases. The electroweak Zjj cross section is extracted and found to be in good agreement with theory predictions. Limits are also placed on anomalous triple gauge couplings. The commissioning of an event filter isolated muon trigger is also presented. The trigger became one of the primary muon triggers used during the 2012 data taking.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第22027号 / 理博第4531号 / 新制||理||1651(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)准教授 菅沼 秀夫, 教授 大西 明, 教授 田中 貴浩 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

Lattice gauge theory is a special regularization of continuum gauge theories and the numerical simulation of lattice quantum chromodynamics (QCD) remains as the only first principle method to study non-perturbative QCD at low energy. The lattice spacing a, which serves as the ultraviolet cut off, plays a significant role in determining error on any lattice simulation results. Physical results come from extrapolating a series of simulations with different values for a to a=0. Reducing the size of these errors for non-zero a improves the extrapolation and minimizes the error. In the strong coupling limit the coarse lattice spacing pushes the analysis of the finite lattice spacing error to its limit. Section 4 measures two renormalized physical observables, the neutral kaon mixing parameter BK and the Delta I=3/2 K pi pi decay amplitude A2 on a lattice with coarse lattice spacing of a ~ 1GeV and explores the a^2 scaling properties at this scale. In the weak coupling limit the lattice simulations suffer from critical slowing down where for the Monte Carlo Markov evolution the cost of generating decorrelated samples increases significantly as the lattice spacing decreases, which makes reliable error analysis on the results expensive. Among the observables the topological charge of the configurations appears to have the longest integrated autocorrelation time. Based on a previous work where a diffusion model is proposed to describe the evolution of the topological charge, section 2 extends this model to lattices with dynamical fermions using a new numerical method that captures the behavior for different Fourier modes. Section 3 describes our effort to find a practical renormalization group transformation to transform lattice QCD between two different scales, whose knowledge could ultimately leads to a multi-scale evolution algorithm that solves the problem of critical slowing down. For a particular choice of action, we have found that doubling the lattice spacing of a fine lattice yields observables that agree at the few precent level with direct simulations on the coarser lattice. Section 5 aims at speeding up the lattice simulations in the weak coupling limit from the numerical method and hardware perspective. It proposes a preconditioner for solving the Dirac equation targeting the ensemble generation phase and details its implementation on currently the fastest supercomputer in the world.

Green functions of currents allow us to study resonances in the low- energy limit of QCD. Using them, we can construct amplitudes or decay widths of processes. By a comparison of the theoretical predictions with experimental measurements we can determine the values of parameters of the theory and obtain a more comprehensive understanding about the be- haviour of QCD processes. In our investigated topic, an odd-parity sector of QCD, exist five nontriv- ial three-point Green functions, also referred to as correlators. Correlators V V P and V AS have already been studied in [1], whilst a calculation of AAP was provided in [2]. In this thesis we therefore deal with the Green functions V V A and AAA that have not yet been studied before. We present a complete calculation of the contributing Feynman diagrams in the anti- symmetric tensor formalism that satisfies high-energy behaviour within the OPE framework, as was shown also in [2]. The obtained results are submit- ted to phenomenological studies. Further, we also present an introduction to our calculations of the four- point Green functions V V PP and V V V V . The calculations were carried out both in the antisymmetric tensor and vector formalism but due to the complicated tensor structure of the results, the calculations can not be shown here in their...

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18789号 / 理博第4047号 / 新制||理||1582(附属図書館) / 31740 / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)准教授 菅沼 秀夫, 教授 國廣 悌二, 教授 田中 貴浩 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20902号 / 理博第4354号 / 新制||理||1625(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 國廣 悌二, 教授 川合 光, 教授 杉本 茂樹 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

No description available.

No description available.

No description available.