Usando as Regras de Soma da QCD, testamos se a nova estrutura estreita, X(4350) recentemente observada pela Colaboração Belle, pode ser descrita como um estado molecular DsDs0 exótico JPC = 1+. Consideramos as contribuições dos condensados de dimensão oito, trabalhamos com os termos dominantes em s mantendo os termos lineares na massa do quark estranho ms. A massa obtida é igual a mDsDs0 = (5.05±0.19) GeV. Consideramos também uma corrente molecular 1+, DD0 e obtemos mDD0 = (4.92 ± 0.08) GeV. Concluímos que não é possível descrever a estrutura X(4350) como um estado molecular 1+ DsDs0. / Using the QCD sum rules we test if the new narrow structure, the X(4350) recently observed by the Belle Collaboration, can be described as a JPC = 1+ exotic DsDs0 molecular state. We consider the contributions of condensates up to dimension eight, we work at leading order in s and we keep terms which are linear in the strange quark mass ms. The mass obtained for such state is mDsDs0 = (5.05 ± 0.19) GeV. We also consider a molecular 1+, DD 0 current and we obtain mDD0 = (4.92 ± 0.08) GeV. We conclude that it is not possible to describe the X(4350) structure as a 1+ DsDs0 molecular state

In this thesis we study radiative decays of the exotic meson X(3872) into $J/ \\psi \\gamma$ and $\\psi(2S) \\gamma$ using an effective field theory framework. Assuming the exotic meson to be primarily a molecular state of the mesons $D$ and $ \\bar{D}^{*}$, we perform a renormalization analysis to estimate the contribution of the short-distance physics. This is done using two different prescriptions, the popular $\\overline{MS}$ scheme, valid only for perturbative calculations, and the PDS scheme, used in EFTs for loosely-bound systems and intrinsically non-perturbative. We show that, without a short-distance contact interaction, the observables become very dependent on the regularization scale, therefore demanding proper renormalization. We include two short-distance contact terms, one for each decay channel, and impose the renormalization condition within both $\\overline{MS}$ and PDS schemes. We obtain the behavior of the contact term with the renormalization scale $\\mu$, which can be useful in guiding models for the short-distance part. We note, however, distinct behaviors between $\\overline{MS}$ and PDS. Both also lead to lower limits in the decay widths that could, in principle, be tested experimentally. / In this thesis we study radiative decays of the exotic meson X(3872) into $J/ \\psi \\gamma$ and $\\psi(2S) \\gamma$ using an effective field theory framework. Assuming the exotic meson to be primarily a molecular state of the mesons $D$ and $ \\bar{D}^{*}$, we perform a renormalization analysis to estimate the contribution of the short-distance physics. This is done using two different prescriptions, the popular $\\overline{MS}$ scheme, valid only for perturbative calculations, and the PDS scheme, used in EFTs for loosely-bound systems and intrinsically non-perturbative. We show that, without a short-distance contact interaction, the observables become very dependent on the regularization scale, therefore demanding proper renormalization. We include two short-distance contact terms, one for each decay channel, and impose the renormalization condition within both $\\overline{MS}$ and PDS schemes. We obtain the behavior of the contact term with the renormalization scale $\\mu$, which can be useful in guiding models for the short-distance part. We note, however, distinct behaviors between $\\overline{MS}$ and PDS. Both also lead to lower limits in the decay widths that could, in principle, be tested experimentally.

With the use of chiral theory of mesons [1], [2] we evaluate the decay rate of η′ → π+π−π+π−. Our theoretical study of this problem is different from the previous theo- retical study [3] and our predicted result is in a good agreement with the experiment. In this chiral theory we evaluate Feynman diagrams up to one loop and the decay rate is calculated with the use of triangle and box diagrams. The ρ0 meson includes in both type of diagrams as a resonance state. Divergent integrals in the loop calculations are regularized with the use of n-dimensional ’t Hooft-Veltman regularization technique. At the last step to obtain the decay rate, the phase space integral has been calculated.

LHCb est une expérience dédiée à l'étude de la violation CP dans le système des mésons B et à l'étude de leurs désintégrations rares. En 2000, la collaboration a décidé de modifier son appareillage pour minimiser la matière rencontrée par les particules et optimiser le système de déclenchement. C'est dans ce contexte que se place cette thèse qui comprend trois parties. La première est relative à l'identification des électrons qui est principalement basée sur l'information fournie par le système des calorimètres mais tire aussi profit des mesures du RICH et du détecteurs à muons. L'efficacité d'identification des électrons est environ 94% avec un taux d'identification de pions comme électrons égal à 0.7% et une pureté de l'échantillon d'électrons de 65%. Dans la première partie est aussi présentée la reconstruction des photons Bremsstrahlung, qui permet une sélection du J/psi se désintégrant en paire e+e- et ainsi celle du canal B0d→ J/psi(ee) Ks. La deuxième partie décrit la sélection de ce canal qui consiste en un ensemble de coupures cinématiques et topologiques. L'efficacité totale de sélection est 0.176% correspondant à 28000 événements reconstruits par an, avec un rapport B/S, pour le fond bb inclusif, comprit dans l'intervalle à 90% de niveau de confiance [0.017;0.069]. Enfin, dans la dernière partie sont présentées les méthodes d'étiquetage de la saveur des mésons B. L'ajout de l'information fournie par le détecteur de vertex permet de rejeter les électrons issus de conversion de photon et ainsi d'améliorer sensiblement les performances. Ces performances ont ensuite été utilisées pour déterminer la sensibilité de l'expérience LHCb à la mesure de sin(2beta). L'erreur statistique attendue sur sin(2beta), après un an de prise de données correspondant à une luminosité intégrée de 2 fb-1 et une section efficace de production des paires bb de 0.5 mb, varie de 0,015 à 0.020 en fonction des paramètres sin(2b) et |lambda f| et du niveau de bruit de fond.

In this thesis, we applied Light Cone QCD sum rules (LCSR) to several problems in meson physics. Semileptonic B-&gt / eta l v decays are important to get information on Cabibbo-Kobayashi-Maskawa (CKM) matrix elements. We calculated form factors of this decay in LCSR frame. Our results are confirmed by later studies and these similar studies had been used for enhancing result on b to u quark transition matrix element of CKM matrix by BaBar collaboration. We used LCSR method also for calculating coupling constant of radiative rho -&gt / eta photon decay since the analysis of the vector particle to pseudoscalar particle radiative decay with eta and eta&#039 / mesons in final state can provide insights to the long standing issue of the eta and eta&#039 / mixing. Our result g_{rho eta photon}=(1.4 &plusmn / 0.2) is very close to experimental value g_{ rho eta photon} = (1.42 &plusmn / 0.12). We also calculated magnetic moment of the rho meson in LCSR frame which is an important parameter since it is strongly related to internal structure of hadron. Our result 2.3 &plusmn / 0.5 in units of (e/2m_rho), is in better agreement with lattice QCD results than traditional QCD sum rules. Quark contents of light scalar mesons are still under debate and we analyzed phi -&gt / K K decays which is important for understanding the quark content of the f0 meson. Our final result is g_{phi KK} = 4.9 &plusmn / 0.8 which is in well agreement with existing experimental result g_{phi KK} = 4.8.

Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal

O regime de energia do experimento Large Hadron Collider (LHC) no CERN amplia o espaço de fase para a produção de partículas de uma maneira sem precedentes, possibilitando um estudo mais detalhado das partículas e seus subcomponentes. Muitos processos de espalhamento interessantes para a fenomenologia da QCD em altas energias, principalmente aqueles mediados por troca de objetos sem cor, são caracterizados por partículas emitidas em ângulos de espalhamento muito pequenos em relação ao eixo do feixe incidente. Especialmente em processos de espalhamento, a fração de momentum dos pártons no alvo é aproximadamente x = (M/√s)e−y, onde M é a massa da partícula e √s é a energia de centro de massa, assim pequeno - x está relacionado com a região de grande pseudorapidez (η = −ln[tan θ/2] ≈ y), a qual é denominada região frontal. Esta Tese trata, portanto, da física de pequeno - x em processos frontais no LHC, analisando especificamente a produção dos mésons J/ e (2S) em energias de centro de massa 2.76 TeV em colisões coerentes e incoerentes eletromagnéticas PbPb e a produção de diléptons em colisões pp em energias de centro de massa de 7 TeV . A abordagem utilizada nos cálculos é o formalismo de dipolos de cor, o qual é conveniente em pequeno - x, e apresenta uma forma eficaz e simplificada para o cálculo das seções de choque. As predições apresentadas são consistentes com dados experimentais das colaborações ALICE, E866 e CDF, mostrando a robustez do modelo utilizado. / The Large Hadron Collider (LHC) energy regime extends the phase space for particle production to an unprecedent way, enabling a more detailed study of subatomic particles. Many interesting scattering processes for QCD phenomenology at high energies, specially those mediated by the exchange of objects without color, are characterized by particles emitted in very small scattering angles relative to the axis of incident beam. Specially in scattering processes, the target parton momentum fraction is approximately x = (M/√s)e−y, where M is the particle mass and √s is the center of mass energy. Therefore, small-x is related to the large pseudorapidez region (η = −ln[tan θ/2] ≈ y), which is called forward region. Therefore, this thesis deals with the small-x physics in forward processes at the LHC, specifically analyzing the production of mesons J/ and (2S) at 2.76 TeV center of mass energy in coherent and incoherent electromagnetic PbPb collisions and dileptons production at 7 TeV center of mass energy in pp collisions. The approach used in the calculations is the color dipole formalism, which is convenient in small-x, and presents an effective and simple way to calculate the cross sections. The predictions are consistent with the ALICE, CDF and E866 collaborations experimental data, showing the robustness of the considered model.

O regime de energia do experimento Large Hadron Collider (LHC) no CERN amplia o espaço de fase para a produção de partículas de uma maneira sem precedentes, possibilitando um estudo mais detalhado das partículas e seus subcomponentes. Muitos processos de espalhamento interessantes para a fenomenologia da QCD em altas energias, principalmente aqueles mediados por troca de objetos sem cor, são caracterizados por partículas emitidas em ângulos de espalhamento muito pequenos em relação ao eixo do feixe incidente. Especialmente em processos de espalhamento, a fração de momentum dos pártons no alvo é aproximadamente x = (M/√s)e−y, onde M é a massa da partícula e √s é a energia de centro de massa, assim pequeno - x está relacionado com a região de grande pseudorapidez (η = −ln[tan θ/2] ≈ y), a qual é denominada região frontal. Esta Tese trata, portanto, da física de pequeno - x em processos frontais no LHC, analisando especificamente a produção dos mésons J/ e (2S) em energias de centro de massa 2.76 TeV em colisões coerentes e incoerentes eletromagnéticas PbPb e a produção de diléptons em colisões pp em energias de centro de massa de 7 TeV . A abordagem utilizada nos cálculos é o formalismo de dipolos de cor, o qual é conveniente em pequeno - x, e apresenta uma forma eficaz e simplificada para o cálculo das seções de choque. As predições apresentadas são consistentes com dados experimentais das colaborações ALICE, E866 e CDF, mostrando a robustez do modelo utilizado. / The Large Hadron Collider (LHC) energy regime extends the phase space for particle production to an unprecedent way, enabling a more detailed study of subatomic particles. Many interesting scattering processes for QCD phenomenology at high energies, specially those mediated by the exchange of objects without color, are characterized by particles emitted in very small scattering angles relative to the axis of incident beam. Specially in scattering processes, the target parton momentum fraction is approximately x = (M/√s)e−y, where M is the particle mass and √s is the center of mass energy. Therefore, small-x is related to the large pseudorapidez region (η = −ln[tan θ/2] ≈ y), which is called forward region. Therefore, this thesis deals with the small-x physics in forward processes at the LHC, specifically analyzing the production of mesons J/ and (2S) at 2.76 TeV center of mass energy in coherent and incoherent electromagnetic PbPb collisions and dileptons production at 7 TeV center of mass energy in pp collisions. The approach used in the calculations is the color dipole formalism, which is convenient in small-x, and presents an effective and simple way to calculate the cross sections. The predictions are consistent with the ALICE, CDF and E866 collaborations experimental data, showing the robustness of the considered model.

Usando as Regras de Soma da QCD, testamos se a nova estrutura estreita, X(4350) recentemente observada pela Colaboração Belle, pode ser descrita como um estado molecular DsDs0 exótico JPC = 1+. Consideramos as contribuições dos condensados de dimensão oito, trabalhamos com os termos dominantes em s mantendo os termos lineares na massa do quark estranho ms. A massa obtida é igual a mDsDs0 = (5.05±0.19) GeV. Consideramos também uma corrente molecular 1+, DD0 e obtemos mDD0 = (4.92 ± 0.08) GeV. Concluímos que não é possível descrever a estrutura X(4350) como um estado molecular 1+ DsDs0. / Using the QCD sum rules we test if the new narrow structure, the X(4350) recently observed by the Belle Collaboration, can be described as a JPC = 1+ exotic DsDs0 molecular state. We consider the contributions of condensates up to dimension eight, we work at leading order in s and we keep terms which are linear in the strange quark mass ms. The mass obtained for such state is mDsDs0 = (5.05 ± 0.19) GeV. We also consider a molecular 1+, DD 0 current and we obtain mDD0 = (4.92 ± 0.08) GeV. We conclude that it is not possible to describe the X(4350) structure as a 1+ DsDs0 molecular state

O regime de energia do experimento Large Hadron Collider (LHC) no CERN amplia o espaço de fase para a produção de partículas de uma maneira sem precedentes, possibilitando um estudo mais detalhado das partículas e seus subcomponentes. Muitos processos de espalhamento interessantes para a fenomenologia da QCD em altas energias, principalmente aqueles mediados por troca de objetos sem cor, são caracterizados por partículas emitidas em ângulos de espalhamento muito pequenos em relação ao eixo do feixe incidente. Especialmente em processos de espalhamento, a fração de momentum dos pártons no alvo é aproximadamente x = (M/√s)e−y, onde M é a massa da partícula e √s é a energia de centro de massa, assim pequeno - x está relacionado com a região de grande pseudorapidez (η = −ln[tan θ/2] ≈ y), a qual é denominada região frontal. Esta Tese trata, portanto, da física de pequeno - x em processos frontais no LHC, analisando especificamente a produção dos mésons J/ e (2S) em energias de centro de massa 2.76 TeV em colisões coerentes e incoerentes eletromagnéticas PbPb e a produção de diléptons em colisões pp em energias de centro de massa de 7 TeV . A abordagem utilizada nos cálculos é o formalismo de dipolos de cor, o qual é conveniente em pequeno - x, e apresenta uma forma eficaz e simplificada para o cálculo das seções de choque. As predições apresentadas são consistentes com dados experimentais das colaborações ALICE, E866 e CDF, mostrando a robustez do modelo utilizado. / The Large Hadron Collider (LHC) energy regime extends the phase space for particle production to an unprecedent way, enabling a more detailed study of subatomic particles. Many interesting scattering processes for QCD phenomenology at high energies, specially those mediated by the exchange of objects without color, are characterized by particles emitted in very small scattering angles relative to the axis of incident beam. Specially in scattering processes, the target parton momentum fraction is approximately x = (M/√s)e−y, where M is the particle mass and √s is the center of mass energy. Therefore, small-x is related to the large pseudorapidez region (η = −ln[tan θ/2] ≈ y), which is called forward region. Therefore, this thesis deals with the small-x physics in forward processes at the LHC, specifically analyzing the production of mesons J/ and (2S) at 2.76 TeV center of mass energy in coherent and incoherent electromagnetic PbPb collisions and dileptons production at 7 TeV center of mass energy in pp collisions. The approach used in the calculations is the color dipole formalism, which is convenient in small-x, and presents an effective and simple way to calculate the cross sections. The predictions are consistent with the ALICE, CDF and E866 collaborations experimental data, showing the robustness of the considered model.