The radiative annihilation of K⁻p atoms to Λγ and ∑°γ is investigated using a non-relativistic harmonic oscillator quark model. A nonrelativistic reduction of the first order Feynman diagrams is performed to yield a gauge invariant interaction, which is sandwiched between three quark wave functions. Pseudoscalar and pseudovector coupling schemes are used for the strong vertex and the effects of SU(3)flavour breaking is explored. We obtain results which are in agreement with experiment for the ∑°γ but are somewhat high for the Λγ calculation. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

No description available.

Searches are presented for narrow heavy resonances decaying to a top quark and a bottom quark using data collected by the CMS experiment at a center-of-mass energy of 13 TeV. Final states that include a single lepton (electron, muon), multiple jets, and missing transverse momentum are analyzed. No evidence is found for the production of a W' boson, and the production of right-handed W' bosons is excluded at 95% confidence level for masses up to 3.6 TeV depending on the scenario considered. Exclusion limits for W' bosons are also presented as a function of their coupling strength to left- and right-handed fermions. These limits on a W' boson decaying via a top and a bottom quark are the most stringent published to date. Projections for future searches with an integrated luminosity of up to 3 inverse attobarns are also presented, and suggest that W' boson masses above 4 TeV could be excluded.

Experimentos no RHIC mostram que coLisões centrais Au+Au apresentam forte supressão de partículas em relação a colisões p+p. É possível entender esse fato através de supressão de jatos ou perda de energia de pártons dentro do plasma de quarks e glúons (QGP). Espera-se que essa perda de energia seja menor para partículas que possuem maior massa. Seguindo-se esse raciocínio é natural pensar que a supressão de quarks pesados seja menor que a de quarks leves. No entanto o que é de fato observado é uma supressão tão forte quanto a de quarks Leves. Analisando os modelos de perda de energia pode-se propor uma explicação para essa discrepância. Esses modelos não consideram flutuações nas condições iniciais que podem levar a regiões localizadas de alta densidade no início da colisão. Tais regiões Levariam a uma considerável perda de energia de quarks nesse estágio. Além disso deve-se considerar a dinâmica do meio, sua evolução ao longo do tempo, em que essas regiões podem se mover ou modificar-se. O objetivo deste trabalho é analisar o efeito que essas flutuações nas condições iniciais têm sobre a supressão de quarks pesados no QGP. Isso é feito através de simulações computacionais do modelo proposto de perda de energia, resultado em estimativas do fator de modificação nuclear (RAA) a serem comparadas com dados experimentais. Foram executadas simulações de RAA enquanto se comparam os modelos empregados na simulação com resultados experimentais. Todos os processos da simulação foram extensivamente calibrados para se obter resultados coerentes com os cálculos já presentes na Literatura. Por fim, espectros de RAA foram comparados para diferentes parâmetros de flutuações de condições iniciais. Não foi possível obter variações relevantes no espectro de RAA, indicando que as flutuações, na maneira desenvolvida neste trabalho, não oferecem influência nos cálculos de perda de energia. Contudo o desenvolvimento do trabalho deixa em aberto diversos aspectos da evolução do sistema que ainda podem ser estudados a fim de se conhecer melhor a dinâmica do QGP. / Central Au+Au collisions at RHIC exhibit strong particle suppression when compared to p+p collisions. This phenomenon can be understood in the framework of jet quenching or energy loss of partons inside the quark-gluon plasma (QGP). It is expected that heavier partons suffer less suppression than lighter ones. In this scenario, heavy quarks are less suppressed than light quarks. However, experiments show that heavy quarks are just as suppressed as light quarks. One possible explanation for that can be obtained when considering fluctuations in the medium that lead to high-density regions which can cause considerable quark energy loss at the early stages of the collision evolution. The QGP dynamics is also important as these high-density regions might expand differentty from the rest of the plasma. This work aims to analyse the overall U effect of these fluctuations in heavy quark suppression in the QGP. This can be done through computer simulations of charm and bottom propagating through the region considering different models of energy loss, which will then return an estimate of the nuclear modification factor (RAA). The final results for the RAA spectrum were found not to be affected by the included fluctuations in the initial conditions, meaning that these, in the way implemented here, are not sufficient to observe relevant modifications of the parton energy loss. There is, however, some open issues raised by this work that should be investigated in order to verify this conclusion.

Experimentos no RHIC mostram que coLisões centrais Au+Au apresentam forte supressão de partículas em relação a colisões p+p. É possível entender esse fato através de supressão de jatos ou perda de energia de pártons dentro do plasma de quarks e glúons (QGP). Espera-se que essa perda de energia seja menor para partículas que possuem maior massa. Seguindo-se esse raciocínio é natural pensar que a supressão de quarks pesados seja menor que a de quarks leves. No entanto o que é de fato observado é uma supressão tão forte quanto a de quarks Leves. Analisando os modelos de perda de energia pode-se propor uma explicação para essa discrepância. Esses modelos não consideram flutuações nas condições iniciais que podem levar a regiões localizadas de alta densidade no início da colisão. Tais regiões Levariam a uma considerável perda de energia de quarks nesse estágio. Além disso deve-se considerar a dinâmica do meio, sua evolução ao longo do tempo, em que essas regiões podem se mover ou modificar-se. O objetivo deste trabalho é analisar o efeito que essas flutuações nas condições iniciais têm sobre a supressão de quarks pesados no QGP. Isso é feito através de simulações computacionais do modelo proposto de perda de energia, resultado em estimativas do fator de modificação nuclear (RAA) a serem comparadas com dados experimentais. Foram executadas simulações de RAA enquanto se comparam os modelos empregados na simulação com resultados experimentais. Todos os processos da simulação foram extensivamente calibrados para se obter resultados coerentes com os cálculos já presentes na Literatura. Por fim, espectros de RAA foram comparados para diferentes parâmetros de flutuações de condições iniciais. Não foi possível obter variações relevantes no espectro de RAA, indicando que as flutuações, na maneira desenvolvida neste trabalho, não oferecem influência nos cálculos de perda de energia. Contudo o desenvolvimento do trabalho deixa em aberto diversos aspectos da evolução do sistema que ainda podem ser estudados a fim de se conhecer melhor a dinâmica do QGP. / Central Au+Au collisions at RHIC exhibit strong particle suppression when compared to p+p collisions. This phenomenon can be understood in the framework of jet quenching or energy loss of partons inside the quark-gluon plasma (QGP). It is expected that heavier partons suffer less suppression than lighter ones. In this scenario, heavy quarks are less suppressed than light quarks. However, experiments show that heavy quarks are just as suppressed as light quarks. One possible explanation for that can be obtained when considering fluctuations in the medium that lead to high-density regions which can cause considerable quark energy loss at the early stages of the collision evolution. The QGP dynamics is also important as these high-density regions might expand differentty from the rest of the plasma. This work aims to analyse the overall U effect of these fluctuations in heavy quark suppression in the QGP. This can be done through computer simulations of charm and bottom propagating through the region considering different models of energy loss, which will then return an estimate of the nuclear modification factor (RAA). The final results for the RAA spectrum were found not to be affected by the included fluctuations in the initial conditions, meaning that these, in the way implemented here, are not sufficient to observe relevant modifications of the parton energy loss. There is, however, some open issues raised by this work that should be investigated in order to verify this conclusion.

Un des buts de la collaboration COMPASS est l'étude de la structure de spin du nucléon. La question de la polarisation des quarks de la mer est un sujet capital en physique hadronique, en particulier pour la polarisation du quark étrange. En vue de mieux contraindre la polarisation des quarks, une connaissance précise des fonctions de fragmentation (FFs), qui expriment l'hadronisation d'un quark q en un hadron h dans l'état final, est nécessaire. Les FFs peuvent être extraites depuis les multiplicités de hadrons produites en diffusion inélastique profonde semi-inclusive (SIDIS). Les données ont été prises à COMPASS avec un faisceau de muons de 160 GeV/c diffusant sur une cible de protons pure (1H₂). La présente thèse présente les mesures des multiplicités de hadrons chargés (pions, kaons et protons) faites à partir des données SIDIS collectées en 2016. Elle détaille aussi les améliorations apportées au générateur d'événement DJANGOH dans le but d'améliorer la description des corrections radiative inclusive et semi-inclusive qui sont ensuite utilisées comme facteurs de corrections aux multiplicités. Les données couvrent un large spectre cinématique : Q² > 1 (GeV/c)², y ε [0.1,0.7], x ε [0.004,0.4], W ε [5,17] GeV et z ε [0.2,0.85]. Ces multiplicités, qui représentent un total d'environ 1800 points de données, apportent une contribution importante aux fit QCD globaux des données mondiales à NLO, visant à la détermination des FFs. Les FFs de quarks en kaons sont particulièrement attendues car elles pourront mieux contraindre la polarization du quark étrange. / One of the goals of the COMPASS collaboration is the study of the nucleon spin structure. The question of the polarization of the sea quark is a burning issue in the hadronic physics, especially for the strange quark polarization. In order to better constrain the quark polarization, a precise knowledge of the quark Fragmentation Functions (FFs) into hadrons, which are the final state hadronisation of quark q into hadron h, is mandatory. The FFs can be extracted from hadron multiplicities produced in Semi-Inclusive Deep Inelastic Scattering (SIDIS). Data were taken at COMPASS from a 160 GeV/c muon beam scattering off a pure proton target (1H₂). This thesis presents the measurement of charged hadrons (pions, kaons and protons) multiplicities from SIDIS data collected in 2016. It also details the improvements brought to the DJANGOH event generator to better describe the inclusive and semi-inclusive radiative corrections in DIS that are then used as correction factors to the multiplicities. The data cover a large kinematical range : Q² > 1 (GeV/c)², y ε [0.1,0.7], x ε [0.004,0.4], W ε [5,17] GeV et z ε [0.2,0.85]. These multiplicities, which represent about 1800 data points in total, provide an important input for global QCD fit of world data at NLO, aiming at the FFs determination. The quark FFs into kaons are particularly awaited as they can better constrain the strange quark polarization.

Cette thèse présente une étude de la production associée du boson de Higgs en association avec des quarks tops, suivie d’une désintégration du boson de Higgs en leptons tau, dans des collisions proton-proton (pp) à une énergie dans le centre de masse de sqrt(s) = 13 TeV enregistrées avec le détecteur CMS au Grand collisionneur de hadrons (LHC) du CERN.Ce travail s’inscrit dans le contexte du Run 2 du LHC, marqué par une augmentation de l’énergie dans le centre de masse de 8 à 13 TeV accompagnée d’une augmentation de la luminosité instantanée des collisions par rapport au Run 1. Pour faire face à ces nouvelles conditions de prise de données, CMS a entrepris une amélioration complète du système de déclenchement de niveau 1 accomplie avant 2016. Ce nouveau système et en particulier le nouvel algorithme électron et photon de niveau 1 ont contribué avec succès à un grand nombre de résultats CMS basés sur les données du Run 2. La mise en service de ce nouveau système ainsi que ces performances mesurées dans les premières données collectées par ce nouveau système de déclenchement sont présentées en détails.Une technique d’analyse novatrice basée sur la Méthode des Éléments de Matrice optimisée pour la recherche du processus ttH, H->tautau est également présentée, ainsi que plusieurs outils génériques pouvant âtre utilisés dans une large variété d’analyses H->tautau. Les résultats de l’analyse CMS utilisant cette méthode basés sur 35.9 fb-1 collectés en 2016 sont présentés. L’hypothèse "bruit de fond seul" est défavorisée mais n’est pas encore exclue par cette analyse à elle seule. / This thesis reports a study of the Higgs boson production in association with top quarks and decaying into τ leptons in proton-proton (pp) collisions at a center-of-mass energy of sqrt(s) = 13 TeV recorded with the CMS detector at the CERN Large Hadron Collider (LHC).This work has been carried out in the context of the Run 2 of the LHC, marked by an increase in the center-of-mass energy from 8 to 13 TeV together with an increase in the instantaneous luminosity of the collisions with respect to Run 1. To cope with this new data-taking conditions, CMS had initiated a full upgrade of the Level-1 trigger system achieved by 2016. This new system and in particular the new Level-1 electron and photon algorithm have successfully contributed to a large number of CMS results using Run 2 data. The commissioning of this new system and its performance measured with the first data collected with this new trigger are presented in details.A novel analysis technique based on the Matrix Element Method optimized for the search of the ttH, H->tautau process is also presented, including several generic tools which can be used in a large variety of H->tautau analyses. Results of the CMS analysis using this method based on 35.9 fb-1 collected in 2016 are presented. The background-only hypothesis is disfavored but not yet excluded by this analysis alone.

<p>The top quark is the most massive known elementary particle, and plays a pivotal role in our understanding of particle physics. Its unique properties offer valuable insights into the Standard Model and potential hints for physics beyond the Standard Model. In this thesis we present a precision measurement of the polarization of top quarks and spin correlations between top-antitop (ttbar) pairs using Run-II datasets collected from the Compact </p> <p>Muon Solenoid detector at the Large Hadron Collider. In the first part of this thesis we introduce the theoretical framework of the Standard Model and its predictions regarding top quark spin polarization and ttbar spin correlations. Next, we describe the experimental setup, reconstruction techniques, and Monte Carlo simulations used in this research. Subsequently, details of the measurement, including event selection, top quark reconstruction, and unfolding are described. The analysis achieves exceptional signal purity and precision with respect to previous measurements. The measured values of coefficients are in agreement with Standard Model expected values as well as theoretical predictions at NLO in QCD. In a first, we provide provide double-differential cross sections of top quark spin polarizations and ttbar spin correlations, as a function of the invariant mass of the ttbar system. We expect the results from the final CMS publication to supersede any results presented in the measurement part of this thesis document. In the final section of this thesis, we present a projection study of top quark spin polarization and tt ̄ spin correlations at the upcoming High Luminosity LHC. We present projections of the fraction of SM-like events and show that the upcoming detector could reduce uncertainties by as much as a factor 2. An alternative to the SM scenario is also considered in the form of Super Symmetry, and it is shown that we can significantly increase the ultimate reach of the LHC to discover top squarks in the degenerate mass corridor in the top squark-neutralino plane, or in the absence of a discovery exclude top squarks up to 600 GeV. </p>

A measurement of the fraction, f⁺, of right-handed W bosons produced in top quark decays is presented. This analysis is based on a sample corresponding to an integrated luminosity of 370 pb⁻¹, collected by the D⊘ detector at the Fermilab Tevatron pp Collider at √s = 1.96 TeV. The helicity angle, θ*, is reconstructed for each lepton. f⁺ is determined by comparing the cos θ* distribution from the data with that for the expected background and signal for various values of f⁺. The fraction of longitudinal W bosons, f⁰, is assumed to be 0.7 as predicted by the standard model. This yields f⁺ = 0.109 ± 0.094 (stat) ± 0.063 (syst), consistent with the standard model prediction of f⁺ = 3.6× 10⁻⁴. The possibility that both f⁺ and f⁰ stray from standard model values is also investigated. In this case cos θ* distributions for each possible W helicity state, along with the backgrounds, are fit to the cos θ* distribution for the data. The best fit values are f⁺ = 0.82 ± 0.30(stat) and f⁰ = −0.58 ± 0.50(stat).

No description available.