In this thesis, we study the soft gluon corrections to hard wide-angle scattering processes due to a virtual gluon exchange (one-loop order) and the emission of up to two gluons. Our primary aim is to determine the ordering condition that should be used to dress a hard scattering process with corrections due to gluon emissions and a Coulomb (Glauber) gluon exchange. We find that, due to an elegant cancellation of many Feynman diagrams, a specific ordering variable should be used to order the transverse momentum of the exchanged Coulomb gluon with respect to the real emissions. Furthermore, in the case of the scattering process accompanied with a single emission, we find that the radiative part of the loop correction satisfies the same ordering condition as the Coulomb gluon contribution. Based upon the assumption that the ordering condition continues at higher orders, we conjecture an expression for the soft corrections to a general hard scattering process due to one-loop and any number of gluon emissions.

Two precision measurements have been performed using the large number of dileptonand diphoton events produced in pp¯ and pp collisions. A measurement of thedistribution of the kinematic variable φ∗ηin the Drell-Yan process is performed inbins of boson rapidity and invariant mass using 10.4 fb−1 data collected by the D0experiment with a centre-of-mass energy of 1.96 TeV in pp¯ collisions. φ∗η, definedin terms of lepton track directions, is well-measured and is sensitive to higher ordereffects in Quantum chromodynamics (QCD). Data are compared to predictions fromstate-of-the-art QCD Monte Carlo programs and are in good agreement. Measurementsof the production of prompt photon pairs are performed using 20.24 fb−1 datacollected by the ATLAS experiment at 8 TeV in pp collisions. QCD Monte Carloprograms including higher order effects are found to describe the data. In addition,a luminosity algorithm that renders its susceptibility to noise and inefficiency of certainmodules in the diamond beam monitor has been proposed and validated usingATLAS simulations.

Cette thèse a utilisé la méthode des règles de somme de QCD pour étudier la nature des résonances du charmonium suivantes: Y(3930), Y(4140), X(4350), Y(4260), Y(4360) et Y(4660). Il y a des fortes indications que ces états ont des structures hadroniques non conventionnelles (ou exotiques) lorsque leurs masses respectives et les modes de désintégration observés expérimentalement sont incompatibles avec ce qui est attendu pour l'état conventionnel du charmonium.Le même phénomène se produit dans le secteur du bottomonium, où les nouveaux états Yb(10890) et Yb(11020), observeés récemment pourraient indiquer l'existence de nouveaux états exotiques du bottomonium. De cette façon, on vérifie que l'état Y(4140) peut être décrit soit par une structure moléculaire D*s D*s (0++) ou par une mélange entre les états moléculaires D*s D*s (0++) et D*D* (0++). Les états Y(3930) et X(4350) ne peuvent pas être décrites par les courants moléculaires D*D* (0++) et D*s D*so (1-+), respectivement. On vérifie également que la structure moléculaire psi' f0(980) (1--) réproduit très bien la masse de l'état Y(4660). Une extension naturelle au secteur du bottomonium indique que l'état moléculaire Y' f0(980) est un bon candidat pour l'état Yb(10890). On a également fait une estimation pour les états moléculaires possibles formées par des mésons D et B, ce qui pourra être observé dans des expériences futures au LHC.Une vaste étude, en utilisant le formalisme habituel des règles de somme et aussi le Double Rapport des règles de somme, est fait pour calculer les masses des baryons lourds en QCD. Les estimations pour les masses des baryons avec un (Qqq) et deux (QQq) quarks lourds sont un excellent test pour la capacité de la méthode de règles de somme à prédire les masses des baryons qui n'ont pas encore été observés. / The QCD sum rules approach was used to study the nature of the following charmonium resonances: Y(3930), Y(4140), X(4350), Y(4260), Y(4360) and Y(4660). There is strong evidence that these states have a non-conventional (or exotic) hadronic structures since their respective masses and decay channels observed experimentally are inconsistent with expected for a conventional charmonium state. The same phenomenon occurs on the bottomonium sector, where new states like Yb(10890) and Yb(11020) observed recently could indicate the existence of new bottomonium exotic states. In this way, one verifies that the state Y(4140) could be described as a D*s D*s (0++) molecular state or even as a mixture of D*s D*s (0++) and D*D* (0++) molecular states. For the Y(3930) and X(4350) states, both cannot be described as a D*D* (0++) and D*s D*s0 (1−+), respectively. From the sum rule point of view, the Y(4660) state could be described as a ψ' f0(980) (1−−) molecular state. The extension to the bottomonium sector is done in a straightforward way to demonstrate that the Y' f0(980) molecular state is a good candidate for describing the structure of the Yb(10890) state. In the following, one estimates the mass of the exotic Bc-like molecular states using QCD sum rules - these exotic states would correspond to a bound states of D(*) and B(*) mesons. All of these mass predictions could (or not) be checked in a near future experiments at LHC.A large study using the Double Ratio of sum rules approach has been evaluated for the study of the heavy baryon masses in QCD. The obtained results for the baryons with one (Qqq) and two (QQq) heavy quarks will be an excellent test for the capability of the sum rule approach in predicting mass of the baryons which have not yet been observed.

Predictions of heavy quark parameters are an integral component of precision tests of the Standard Model of particle physics. Experimental measurements of electroweak processes involving heavy hadrons provide stringent tests of Cabibbo-Kobayashi-Maskawa (CKM) matrix unitarity and serve as a probe of new physics. Hadronic matrix elements parameterise the strong dynamics of these interactions and these matrix elements must be calculated nonperturbatively. Lattice quantum chromodynamics (QCD) provides the framework for nonperturbative calculations of QCD processes. Current lattices are too coarse to directly simulate b quarks. Therefore an effective theory, nonrelativistic QCD (NRQCD), is used to discretise the heavy quarks. High precision simulations are required so systematic uncertainties are removed by improving the NRQCD action. Precise simulations also require improved sea quark actions, such as the highly-improved staggered quark (HISQ) action. The renormalisation parameters of these actions cannot be feasibly determined by hand and thus automated procedures have been developed. In this dissertation I apply automated lattice pertubartion theory to a number of heavy quark calculations. I first review the fundamentals of lattice QCD and the construction of lattice NRQCD. I then motivate and discuss lattice perturbation theory in detail, focussing on the tools and techniques that I use in this dissertation. I calculate the two-loop tadpole improvement factors for improved gluons with improved light quarks. I then compute the renormalisation parameters of NRQCD. I use a mix of analytic and numerical methods to extract the one-loop radiative corrections to the higher order kinetic operators in the NRQCD action. I then employ a fully automated procedure to calculate the heavy quark energy shift at two-loops. I use this result to extract a new prediction of the mass of the b quark from lattice NRQCD simulationsby the HPQCD collaboration. I also review the calculation of the radiative corrections to the chromo-magnetic operator in the NRQCD action. This computation is the first outcome of our implementation of background field gauge for automated lattice perturbation theory. Finally, I calculate the heavy-light currents for highly-improved NRQCD heavy quarks with massless HISQ light quarks and discuss the application of these results to nonperturbative studies by the HPQCD collaboration.

Hadrons containing heavy quarks, in particular b quarks, play an important role in high energy physics. Measurements of their electroweak interactions are used to test the Standard Model and search for new physics. For the comparison of experimental results with theoretical predictions, nonperturbative calculations of hadronic matrix elements within the theory of quantum chromodymanics are required. Such calculations can be performed from first principles by formulating QCD on a Euclidean spacetime grid and computing the path integral numerically. Including b quarks in lattice QCD calculations requires special techniques as the lattice spacing in present computations usually can not be chosen fine enough to resolve their Compton wavelength. In this work, improved nonrelativistic lattice actions for heavy quarks are used to perform calculations of the bottom hadron mass spectrum and of form factors for heavy-to-light decays. In heavy-to-light decays, additional complications arise at high recoil, when the momentum of the light meson reaches a magnitude comparable to the cutoff imposed by the lattice. Discretisation errors at high recoil can be reduced by working in a frame of reference where the heavy and light mesons move in opposite directions. Using a formalism referred to as moving nonrelativistic QCD (mNRQCD), the nonrelativistic expansion for the heavy quark can be performed around a state with an arbitrary velocity. This dissertation begins with a review of the fundamentals of lattice QCD. Then, the construction of effective Lagrangians for heavy quarks in the continuum and on the lattice is discussed in detail. A highly improved lattice mNRQCD action is derived and its effectiveness is demonstrated by nonperturbative tests involving both heavy-heavy and heavy-light mesons at several frame velocities. This mNRQCD action is then used in combination with a staggered action for the light quarks to calculate hadronic matrix elements relevant for rare B decays, including B --> K* gamma and B --> K l l. A major contribution to the uncertainty of the results also comes from statistical errors. The effectiveness of random-wall sources to reduce these errors is studied. As another application of a nonrelativistic heavy quark action, the spectrum of bottomonium is calculated and masses of several bottom baryons are predicted. In these computations, the light quarks are implemented with a domain wall action.

New fundamental observables are becoming accessible with the Leading Proton Spectrometers (LPS) of ZEUS and H1. This enables us to test more thoroughly the pQCD mechanism of diffractive Deep Inelastic Scattering (DIS). Calculations of the diffractive cross-section in the small Bjorken x limit have been performed. We have used the microscopic QCD formalism of diffractive DIS to find higher twist corrections to the transverse structure functions and predict the diffractive slope and azimuthal asymmetries. We establish duality correspondence between diffraction into low-mass continuum and vector meson production, and calculate the diffractive contribution to the spin structure functions. / Ph. D.

Il est établi depuis maintenant 40 ans que l'interaction nucléaire forte peut être décrite par la Chromodynamique Quantique (QCD). Le confinement des quarks dans cette théorie masque cependant ses degrés de liberté élémentaires dans les processus de basse énergie, qui doivent être calculés non-perturbativement. La QCD sur réseau est à ce jour la seule méthode permettant de mener à bien de tels calculs, et arrive dorénavant à maturité. Cependant, et alors que le spectre des hadrons stables est calculée avec précision, l'étude des désintégrations reste délicate. Nous présentons ici l'application du formalisme de Lüscher au calcul des propriétés de résonances se désintégrant sous l'interaction forte, ainsi qu'un calcul avec précision de la largeur de désintégration dans le cas particulier du meson rho. / It has been established for now 40 years that the strong nuclear interaction can be described by Quantum Chromodynamics (QCD). However, the confinement of quarks in this theory hides its elementary degrees of freedom in low-energy processes, which have to be computed non-pertubatively. Lattice QCD is, to date, the only method allowing to go through such a computation, and is now reaching maturity. However, although the spectrum of stable hadrons is computed with precision, the study of decays is still delicate. We hereby present the application of Lüscher's formalism to the study of strong-decaying resonance properties, along with a precise computation of the decay width in the particular case of the rho meson.

Usamos as regras de soma da QCD para obter a massa dos pentaquarks \" \'teta\' POT.+\"(1540) e \"\'ksi\' POT.--\" (1862), a largura de decaimento da \"\'teta\' POT.+\" e a constante de acoplamento e fator de forma presentes no vertice J/ \'psi\' \"DD POT.*\". No estudo dos pentaquarks, usamos dois tipos de campos interpolantes contendo dois diquarks altamente correlacionados. Obtemos as massas consistentes com os dados experimentais, porém esta regra de soma têm uma grande contribuição do contínuo e a OPE não é muito boa. Obtivemos uma largura de decaimento compatível com os valores experimentais desde que sejam subtraídos diagramas que representam a \" \'teta\' POT.+\" como um estado ligado K - n. No estudo do vértice vertice J/ \'psi\' \"DD POT.*\" calculamos o fator de forma e a constante de acoplamento, considerando três casos: D off-shell, \"D POT.*\" off-shell e J/ \'psi\' off-shell. A constante de acoplamento é a mesma nesses três casos, porém o fator de forma depende da escolha da partícula off-shell, onde para a J/ \'psi\' off-shell o fator de forma é bem mais duro que o fator de forma obtido para os outros casos. Também comparamos os nossos resultados com outros métodos: o modelo de quark méson constituintes e o modelo de quarks relativísticos constituintes / We use the QCD sum rules to obtain the masses of the pentaquarks _+(1540) and _−−(1862), _+ decay width and the coupling constant and the form factor for the J/ DD* vertex.In the study of the pentaquarks, we use two kinds of interpolating fields, containing two highly correlated diquarks. We get the masses in a good agreement with the experimental value, but this sum rule has a large continuuum contribution and the OPE convergence is not so good. We get the decay width compatible with the experimental value, since we subtract the diagrams that represent _+ as a K − n bound state. In the study of J/ DD* vertex, we calculate the form factor and the coupling constant considering three cases: D off-shell, D* off-shell and J/ off-shell. The coupling constant is the same in those three cases, however the form factor depends on the choice of the particle off-shell, where for the J/ off-shell the form factor is much harder than the form factor obtained for the other cases. We also compare our results with other methods: the constituent quark meson model and the relativistic constituent quark model.

Usamos as regras de soma da QCD para obter a massa dos pentaquarks \" \'teta\' POT.+\"(1540) e \"\'ksi\' POT.--\" (1862), a largura de decaimento da \"\'teta\' POT.+\" e a constante de acoplamento e fator de forma presentes no vertice J/ \'psi\' \"DD POT.*\". No estudo dos pentaquarks, usamos dois tipos de campos interpolantes contendo dois diquarks altamente correlacionados. Obtemos as massas consistentes com os dados experimentais, porém esta regra de soma têm uma grande contribuição do contínuo e a OPE não é muito boa. Obtivemos uma largura de decaimento compatível com os valores experimentais desde que sejam subtraídos diagramas que representam a \" \'teta\' POT.+\" como um estado ligado K - n. No estudo do vértice vertice J/ \'psi\' \"DD POT.*\" calculamos o fator de forma e a constante de acoplamento, considerando três casos: D off-shell, \"D POT.*\" off-shell e J/ \'psi\' off-shell. A constante de acoplamento é a mesma nesses três casos, porém o fator de forma depende da escolha da partícula off-shell, onde para a J/ \'psi\' off-shell o fator de forma é bem mais duro que o fator de forma obtido para os outros casos. Também comparamos os nossos resultados com outros métodos: o modelo de quark méson constituintes e o modelo de quarks relativísticos constituintes / We use the QCD sum rules to obtain the masses of the pentaquarks _+(1540) and _−−(1862), _+ decay width and the coupling constant and the form factor for the J/ DD* vertex.In the study of the pentaquarks, we use two kinds of interpolating fields, containing two highly correlated diquarks. We get the masses in a good agreement with the experimental value, but this sum rule has a large continuuum contribution and the OPE convergence is not so good. We get the decay width compatible with the experimental value, since we subtract the diagrams that represent _+ as a K − n bound state. In the study of J/ DD* vertex, we calculate the form factor and the coupling constant considering three cases: D off-shell, D* off-shell and J/ off-shell. The coupling constant is the same in those three cases, however the form factor depends on the choice of the particle off-shell, where for the J/ off-shell the form factor is much harder than the form factor obtained for the other cases. We also compare our results with other methods: the constituent quark meson model and the relativistic constituent quark model.

A teoria de perturba ca o quiral (ChPT) e aceita, atualmente, como a teoria efetiva da cromodinamica quantica (QCD) para baixas energias. Ela foi colocada na sua versa o moderna com os artigos de Gasser e Leutwyler, na primeira metade da d ecada de 80 e, durante os 25 anos que se seguiram, ocorreu um aumento considera vel da variedade de fenomenos por ela descritos, sempre acompanhando a precisa o cres- cente dos resultados experimentais. Os trabalhos que apresentamos nesta tese de doutorado se inserem neste contexto e envolvem duas partes, ambas relacionadas a` determina c ao de alguns dos parametros que compo em a lagrangiana da ChPT. Por ser uma teoria efetiva, tais constantes s o podem ser fixadas por experimentos, modelos ou por c alculos da QCD na rede. Em um dos trabalhos, discutimos a cons- tante de decaimento do p on, F, e os efeitos decorrentes do acr escimo de intera co es eletromagn eticas a` ChPT. N os argumentamos que as incertezas estimadas para o valor mais aceito de F podem estar subestimadas. Mostramos, tamb em, que na o se pode determinar esta constante na presen ca das intera co es eletromagn eticas, pois a grandeza de onde ela e extra da adquire uma dependencia no calibre utilizado no ca lculo e tem suas propriedades alteradas drasticamente. No outro trabalho, abor- damos os fatores de forma escalares dos m esons pseudoescalares em tres sabores. A partir dos resultados obtidos com a ChPT e do uso de um modelo que trata dos fatores de forma no espa co das posi co es, conseguimos escreve-los em termos ape- nas das constantes presentes na lagrangiana em ordem dominante da ChPT, F e as massas dos m esons pseudoescalares. No s determinamos, tamb em, os respectivos raios quadra ticos m edios e, comparando-os com os calculados com a ChPT, obtive- mos as LECs L4(mu) = -0,26 · 10^-3 e L5(mu) = 0,85 · 10^-3, para mu = 770 MeV. Esses valores sa o compat veis com as principais estimativas vindas da ChPT. / At present, chiral perturbation theory (ChPT) is considered the effective theory of quantum chromodynamics (QCD) at low energies. It was established in its modern version by the papers of Gasser and Leutwyler written in the first half of the 80s. For the last 25 years, there has been considerable increase in the number of phe- nomena described by ChPT, always following the growing precision of experiments. The two works we present in this Ph.D. thesis are related to ChPT and discuss the determination of some of the parameters that appear in the ChPT lagrangian. As ChPT is an effective theory, such constants can only be fixed by experiments, models or calculations in the lattice. In the first presented work, we discuss the pion decay constant, F, and how it is changed by the inclusion of electromagne- tic interactions. We argue that the uncertainty of the most accepted value of F might be underestimated. We also show that we cannot determine this constant in the presence of electromagnetic interactions because the function from which it is extracted acquires a gauge dependence and the functions properties drastically change. In the other work, we deal with pseudoscalar meson scalar form factor in three flavors. We manage to write the form factors only in terms of constants present in ChPT lagrangian at leading order, F and masses of pseudoscalar mesons, using ChPT results and the model that deals with form factors in coordinate space. We also determine the respective square radii and, comparing these to those calculated using ChPT, we have obtained L4(mu) = -0.26 · 10^-3 and L5(mu) = 0.85 · 10^-3, for mu = 770 MeV. These values are compatible with the main estimates evaluated with ChPT.