Neste trabalho usamos uma descrição relativística via troca de mésons em aproximação de campo médio para estimar as energias de partícula-única do hipernúcleo 16∑O. Embora o método usado seja bastante simples, comparado com o método aotoconsistente, os resultados obtidos reproduzem bem as energias e o dedobramento spin-óbita do núcleo 16 0 e estão muito próximos dos previstos na literatura para o hipernúcleo 16∑O. / An estimation of single particle energies for the 16∑O hypernucleus has been done in a relativistic description with exchange of mesons in the mean field approximation. In spite of the simplicity of the method used, as compared with the selfconsistent one, our results reproduce well the energies and the spin-orbit splitting of the 16 0 nucleus and are very close to results presented in the literature for the 16∑O hypernucleus.

A representação de Fock-Tani é um formalismo de teoria de campos para tratar problemas envolvendo simultaneamente partículas compostas e seus constituintes. O formalismo foi originalmente desenvolvido para tratar problemas de física atômica e mais tarde estendido para problemas da física hadrônica. Nesta dissertação, inicialmente apresentamos uma breve revisão da Cromodinâmica Quântica e um detalhado estudo dos modelos de decaimentos. Revisamos também a representação de Fock-Tani para mésons e buscamos estendê-la para incluir processos de decaimento de mésons. Há muito tempo os modelos de criação de pares para decaimentos hadrônicos fortes têm sido formulados. O modelo 3P0 é um típico modelo de decaimento que considera apenas decaimentos do tipo OZI-permitidos para as interações fortes. O modelo 3P0 descreve a criação de um par quark-antiquark adicional na presença do méson do estado inicial. Neste modelo o par quark-antiquark criado tem os números quânticos do vácuo. Este modelo também pode ser formulado pelo limite não-relativístico de um Hamiltoniano de criação de par. Mostrado que a aplicação da transformação de Fock-Tani ao Hamiltoniano de criação de par produz a característica expansão em potências da função de onda, onde o modelo 3P0 é obtido em ordem mais baixa desta expansão e representado pelo Hamiltoniano HFT. O passo seguinte é a introdução das correções de ortogonalidade para corrigir o modelo de “ordem zero”. O Hamiltoniano associado á correção contém termos que dependem de apenas uma Δ, chamado de kernel de estado ligado. É, então proposto o modelo 3P0 corrigido, que é chamado de C3P0. Para obter o modelo C3P0 é feita hipótese da soma, onde uma aproximação é introduzida no sentido de representar efetivamente o resultado da soma da série de potência em Δ. O modelo é aplicado ao decaimento de dois mésons leves: ρ → π + π e b1 → ω + π. As amplitudes e suas respectivas taxas de decaimento são avaliadas. No caso do decaimento de b1 é ainda calculado a razão aD/aS. / Fock-Tani is a field theory formalism appropriated for the simultaneous treatment of composite particles and their constituents. The formalism was originally developed for the treatment of problems in atomic physics and it was extended later on to the treatment of problems on hadron physics. In this dissertation, we initially present a bried review of Quantum Cromodynamics and a more detailed survey of the decay models. For a long time the pair creation models for strong hadronic decays have been formulated. The 3P0 model is typical decay model which considers only OZI-allowed strong decays. The 3P0 model considers a quark-antiquark par creation in the presence of the initial state meson. The quark-antiquark par is created with the vacuum quantum numbers. This model can also be obtained from the non-relativistic limit of the pair creation Hamiltonian. Applying the Fock-Tani transformation to the pair creation Hamiltonian produces the characteristic expansion in powers of the wave function, where the 3P0 model is the lowest order term of this expansion and represented by the Hamiltonian HFT . The next step is to introduce the orthogonality corrections to this “zero order” model. The Hamiltonian associated to this correction contains terms dependent on only one Δ, called the bound state kernel. A new model is introduced in order to correct the 3P0, which we call the C3P0 model. To obtain the C3P0 model the sum hypothesis will be introduced, in order to represent effectively the sum of the Δ power series. The model is applied to the decay of two light meson: ρ → π + π e b1 → ω + π. The decay amplitudes and rates are evaluated. For the b1 decay the aD/aS ratio is calculated.

This thesis focuses on two parts, the evidence of a structure in a four lepton final state, and the CMS detector upgrade studies. The first part of the thesis focuses on an unexpected structure in Υ(1S)l+l− final state, where Υ(1S) → μ+μ−, l can represent a muon or an electron and m(l+l−) is required to be below the Υ(1S) mass. Using an integrated luminosity of 25.6 fb−1 recorded in proton-proton collisions at √s = 7 TeV and √s = 8 TeV with the CMS detector at the CERN LHC, an excess in the mass distribution near 18.5 GeV of Υ(1S)l+l− is found. The mass of this enhancement is found out to be 18.4 ± 0.1 (stat.) ± 0.2 (syst.) GeV in the Υ(1S)μ+μ− channel, and 18.5 ± 0.2 (stat.) ± 0.2 (syst.) GeV in the Υ(1S)e+e− channel. For the two results combined, the enhancement is found out to be 18.4 ± 0.1 (stat.) ± 0.2 (syst.) GeV with a local statistical significance of 4.9 standard deviations and a global significance, after taking into account the look-elsewhere-effect, of 3.6 standard deviations. The width of the observed enhancement is consistent with the mass resolution of the CMS detector. The second part of the thesis focuses on detector upgrade studies for the silicon detector. The LHC has been increasing and will increase the luminosity and collision energy. Due to radiation damage and increasing data loss, the CMS detector underwent a Phase I upgrade in 2016/2017 and will undergo a Phase II upgrade in 2018/2019. In Phase I upgrade, silicon sensors and DC-DC converters were tested at Fermilab for the CMS Forward Pixel detector. For Phase II upgrade, a gantry robot system is built for module assemble at Fermilab for the CMS Outer Tracker detector.

L'expérience BABAR, située à SLAC (Stanford, Californie), étudie depuis 1999 les désintégrations des mésons $B$ produits dans des collisions électron positron à une énergie dans le centre de masse égale à la masse de la résonance $\Upsilon(4S)$. L'identification des particules chargées dans cette expérience utilise pour partie la mesure de la perte d'énergie par unité de longueur dans la chambre à dérive. Afin d'améliorer la calibration de cette quantité, une sélection d'électrons/positrons à partir d'événements Bhabha radiatifs a été développée, elle a permis de réduire l'asymétrie de charge dans la reconstruction des particules chargées. Dans les désintégrations des mésons $B$, la production inclusive des particules charmées ($D^0$, $\overline(D)^0$, $D^(\pm)$ , $D_s^(pm)$, $\Lambda_c^(\pm)$) est mesurée au moyen d'une nouvelle méthode, possible grâce à la grande statistique accumulée par l'expérience BABAR. Les mésons $B$ sont produits par paires à partir de la résonance $\Upsilon(4S)$. Les événements sont sélectionnés en reconstruisant complètement un $B$ dans un mode hadronique. Les particules charmées provenant du second $B$ sont alors reconstruites avec les traces restantes. Ceci permet de mesurer les nombres totaux de charmes produits lors des désintégrations des $B^+$ et des $B^0$ en séparant la production de charmes corrélés (transitions entre quarks: $b\rightarrow c X$) de la production anti-corrélée (transitions entre quarks: $b\rightarrow\overline(c) X$). Les résultats, obtenus avec une luminosité intégrée de $210 fb^(-1)$, sont les suivants~: \begin(displaymath) \begin(array)(l@(=\ ) c @(\hspace(1.5 cm)) l @(=\ ) c r ) N_(c)^(B^+) & 0.970 \pm 0.042 & N_(\overline(c))^(B^+) & 0.262\pm0.034 & \\ N_(c)^(B^0) & 0.950 \pm 0.057 & N_(\overline(c))^(B^0) & 0.285\pm0.048 &. \\ \end(array) \end(displaymath) Cette méthode permet également de mesurer, pour la première fois, les distributions en impulsion des particules charmées dans le référentiel du $B$ qui les a émises, ce qui donne accès aux différents mécanismes de production de ces particules.

The present thesis describes two experiments performed in the storage ring CELSIUS at The Svedberg Laboratory in Uppsala. In the first experiment the importance of three - nucleon clustering in the six - nucelon system was investigated. The total cross section for the production of the ground state and the 3.56 MeV second excited state of 6Li in the 3He(3He,6Li)π+ reaction has been measured at two beam energies, 261.1 and 262.5 MeV, corresponding to center - of - mass energies 1.2 and 1.9 MeV above the production threshold for the 3.56 MeV state. For the ground state the result was 347 ± 84 ± 42 and 92 ± 84 ± 11 nb respectively. The result for the 3.56 MeV state, 104 ± 23 ± 12 and 56 ± 35 ± 7 nb respectively, is compared to the result of a previous study where the 3.56 MeV state was populated in the d(4He,6Li)π0 reaction. In the second experiment a clean sample of 5×105 eta mesons was prepared by means of the d(p,3He)η reaction. Eta production was tagged by the precise determination of the kinetic energy of the associated 3He ions. In the subsequent decay of eta mesons, channels with lepton - anti - lepton pairs were studied in the WASA detector. In a separate study properties of the WASA deuterium pellet target were investigated and in particular the effects on the beam of the beam - target interactions. In both sets of experiments the fused nuclear system was detected by means of a zero - degree spectrometer with a semiconductor detector telescope. Choosing the detectors to match the rather different requirements, precise information regarding the identity and the momentum of the detected ions could be obtained in both cases.

In this thesis we have studied baryon resonances generated from the dynamical interaction of two hadrons. We are interested on this study as an alternative approach to explain the increasing number of observed charmed states which apparently do not fit into the traditional three quark picture of a baryon. In particular, we study baryon molecules with JP = ½ - which can be formed from the attractive interaction of a pseudoscalar meson (0-) and a ground state baryon (1/2+) in s-wave (L = 0). Therefore our aim is to contribute to the understanding of the observed charm baryon spectra by checking if the dynamical origin can explain those states which are candidates to be a baryon resonance with JP =1/2-. The important feature of our model is the description of the meson-baryon interaction in terms of the t-channel vector meson exchange which is fully solved without any approximation. The first part of the thesis is devoted to study these sort of baryon molecules in free space. In order to learn about the nature of a baryon it is important to study its different types of decays. For this reason, we will calculate the strong decays of dynamically generated resonances into meson-baryon components, as well as the electromagnetic transition of such hadron molecules into the lowest-lying ground states. In the second part of the thesis we have included medium and temperature effects on the formalism to study the properties of the charmed baryon resonant states in hot and dense matter. This will allow us as well to study the properties of charmed mesons (D, D, Ds and Ds) in the nuclear medium which will be simultaneously dressed in the self-consistent calculation for the first time. The behaviour of these mesons will influence the charmonium production whose suppression is connected with the possible formation of quark-gluon plasma at a dense matter and high temperature scenario. / En esta tesis se han estudiado las resonancias bariónicas generadas a partir de la interacción dinámica de dos hadrones. Estamos interesados en este estudio como un enfoque alternativo para explicar el creciente número de estados observados con quark encanto y que aparentemente no encajan en la imagen tradicional de tres quarks de un barión. En particular, se estudian las moléculas de bariones con JP = ½ - que pueden formarse a partir de la interacción atractiva de un mesón pseudoescalar (0-) y un barión del estado fundamental ( 1/2+) en onda s (L = 0). Por tanto, nuestro objetivo es comprobar si el origen dinámico puede explicar aquellos estados que son candidatos a ser una resonancia bariónica con JP =1/2-. La característica importante del modelo es la descripción de la interacción mesón-barión en términos del canal t de intercambio de mesones vectoriales, que está resuelto sin ningún tipo de aproximación.La primera parte de la tesis está dedicada a estudiar este tipo de moléculas en el espacio libre. Con el fin de aprender sobre la naturaleza de un barión es importante estudiar sus diferentes tipos de desintegración. Por esta razón, calculamos las desintegraciones fuertes de las resonancias en canales mesón-barión, así como la transición electromagnética a bariones de estado fundamental.En la segunda parte de la tesis se ha incluido en el formalismo los efectos del medio y de la temperatura para estudiar las propiedades de los estados de bariones encantados en materia caliente y densa. Esto nos permitirá también estudiar las propiedades de los mesones encantados (D, D, Ds y Ds) en el medio nuclear, que serán vestidos autoconsistentemente en el cálculo por primera vez. El comportamiento de estos mesones influirá en la producción de “charmonium”, cuya supresión está relacionada con la posible formación de plasma de quark-gluón en materia densa y caliente.

In single A hypernuclei, a A hyperon can occupy any orbital in the hypernucleus since it is free from the Pauli exclusion principle due to its additional quantum number strangeness. Due to the Pauli blocking effect, which suppresses the mesonic decay mode A ->N(pi) in the nuclear medium, hypernuclei larger than (5/A)He decay mainly through the nonmesonic channel, AN-> NN, where the A mass excess of 176 MeV is converted into kinetic energy of a final state of nucleons emerging above the Fermi see. This nonmesonic decay mode is assumed to proceed via the exchange of virtual mesons, and the large momentum transfer involved in the reaction leads to a mechanism that is sensitive to the short-distance behaviour of the amplitude and thus raises the possibility that the exchange of mesons heavier than the pion may play an important role. The fairly large momentum transfer also raises the hope that this reaction turns out to be insensitive to nuclear structure details and thus creates a suitable channel to investigate the weak decay mechanism.

Radiative Decays of the phi-meson to the scalar mesons f0(980) and a0(980) are investigated within the framework of charged kaon loop model for both point-like scalar mesons and for scalar mesons with extended structure. Then, the radiative phi-meson decay into neutral K-meson is studied via a two step mechanism in which the scalar mesons couple the final state to the phi-meson through the charged kaon loop. The branching ratio of this decay is calculated and it is shown that this reaction will not provide a significant background to the measurements of phi-meson into neutral K-meson states decay for testing CP violation.

Quantum Chromodynamics(QCD) is part of the Standard Model(SM) that describes the interaction of fundamental particles. In QCD, due to the fact that strong coupling constant is large at low energies, perturbative approaches do not work. For this reason, non-perturbative approaches have to be used for studying the properties of hadrons. Among several non-perturbative approaches, QCD sum rules is one of the reliable methods which is applied to understand the properties of hadrons and their interactions. In this thesis, the semileptonic rare decays of $B$ meson to $K_{1}(1270)$ and $K_{1} (1400)$ are analyzed in the framework of three point QCD sum rules approach. The $Brightarrow K_{1} (1270,1400) ell^+ ell^-$ decays are significant flavor changing neutral current (FCNC) decays of the $B$ meson, since FCNC processes are forbidden at tree level at SM. These decays are sensitive to the new physics beyond SM. The radiative $Brightarrow K_{1}(1270) gamma$ decay is observed experimentally. Although semileptonic $Bto K_1(1270,1400)$ decays are still not observed, they are expected to be observed at future B factories. These decays happens at the quark level with $brightarrow s ell^+ ell^- $ transition, providing new opportunities for calculating CKM matrix elements: $V_{tb}$ and $V_{ts}$. Applying three point QCD sum rules to $Brightarrow K_{1} (1270,1400) ell^+ ell^-$ decays is tricky, due to the fact that the $K_{1} (1270)$ and $K_{1} (1400)$ states are the mixtures of ideal $^{3}P_{1}(K_{1}^{A})$ and $^{1}P_{1}(K_{1}^{B})$ orbital angular momentum states. First, by taking axial vector and tensor current definitions for $K_1$ mesons, the transition form factors of $Brightarrow K_{1A} ell^+ ell^-$ and $Brightarrow K_{1B} ell^+ ell^-$ are calculated. Then using the definitions for $K_1$ mixing, the transition form factors of $Brightarrow K_{1} (1270,1400) ell^+ ell^-$ decays are obtained. The results of these form factors are used to estimate the branching ratio of $B$ meson into $K_1(1270)$ and $K_1(1400)$. The results obtained for form factors and branching fractions are also compared with the ones in the literature.

This work presents a precision determination of the mass difference of neutral and charged B mesons, m(B0) - m(B+). The measurement is based on a data sample of about 232 million B-meson pairs recorded with the BABAR detector at the e+e- storage-ring system PEP-II. In events of e+e- --> Upsilon(4S) --> B Bbar, B0 and B+ mesons are fully reconstructed in decays B+ --> J/psi K+ and B0 --> J/psi K*0 using the subsequent decays J/psi --> l+ l- and K*0 --> K+ pi- for the reconstruction of J/psi mesons and K*0 resonances, respectively. The determination of the mass difference from the measurement of the invariant B-meson masses suffers from detector-resolution effects. To reach the desired sensitivity, the B-meson momenta are measured in the center-of-mass system, the Upsilon(4S) rest frame. Since their energy is also known in the center-of-mass system, this method leads to the mass difference using the relativistic energy-momentum relation. For this purpose, three different fit methods are performed to the spectra of the B momenta. The obtained result is m(B0) - m(B+) = (+0.33 +- 0.05 +- 0.03) MeV/c^2, where the first error is statistical and the second estimates the systematic uncertainty of this measurement, which agrees well with the current world average. However, the combined error of this measurement is substantially smaller than that in the current world average, and the significance of m(B0) - m(B+) being non-zero has exceeded the 5 sigma level.