La recherche indirecte des effets de la physique au-delà du Modèle Standard à travers les processus de la saveur est complémentaire aux efforts au LHC pour observer directement la nouvelle physique. Dans cette thèse nous discutons plusieurs scénarios au-delà du Modèle Standard (a) en utilisant une approche basée sur les théories de champs effective et (b) en considérant des extensions explicites du Modèle Standard, à savoir les modèles à deux doublets de Higgs et les scénarios postulant l'existence des bosons leptoquarks scalaires à basse énergie. En particulier, nous discutons le phénomène de la brisure de l'universalité des couplages leptoniques dans les désintégrations basées sur les transitions b → sℓℓ et b → cτν, et la possibilité de chercher les signatures de la violation de la saveur leptonique à travers les modes de désintégration similaires. Une proposition pour tester la présence d'un boson pseudoscalaire léger à travers les désintégrations des quarkonia est aussi présentée. / Indirect searches of physics beyond the Standard Model through flavor physics processes at low energies are complementary to the ongoing efforts at the LHC to observe the New Physic phenomena directly. In this thesis we discuss several scenarios of physics beyond the Standard Model by (a) reusing the effective field theory approach and (b) by considering explicit extensions of the Standard Model, namely the two-Higgs doublet models and the scenarios involving the low energy scalar leptoquark states. Particular emphasis is devoted to the issue of the lepton flavor universality violation in the exclusive decays based on b → sℓℓ and b → cτν, and to the possibility of searching for signs of lepton flavor violation through similar decay modes. A proposal for testing the presence of the light CP-odd Higgs through quarkonia decays is also made.

Ein Algorithmus zur Identifizierung von Elektronen mit dem BABAR Detektor wird entwickelt. Basierend auf Spuren, deren Teilchenidentität aus rein kinematischen Überlegungen gefolgert werden kann, wird für Impulse zwischen 0.5 und 2.5 GeV/c die Selektionseffizienz für Elektronen zu 90% bestimmt. Im gleichen Impulsbereich liegt die Wahrscheinlichkeit, Pionen als Elektronen zu identifizieren, zwischen 0.05% und 0.1%. Auf diesem Algorithmus basiert die Messung des inklusiven Elektronen Impulsspektrums aus B-Meson Zerfällen anhand der Daten, die mit dem BABAR Detector am asymmetrischen Speicherring PEP-II ("B-Factory") aufgezeichnet wurden. Das Volumen der analysierten Daten entspricht einer integrierten Luminosität von 4.13 1/fb auf der Y(4S) Resonanz und 0.97 1/fb bei einer um 40 MeV verringerten Schwerpunktsenergie. B - Anti-B Ereignisse werden anhand hochenergetischer Elektronen identifiziert. Elektronen von einem semileptonischen Zerfall des zweiten B-Mesons werden durch die relative Ladung und Impulsrichtung zum hochenergetischen Elektron vom Untergrund aus semileptonischen Charm Zerfällen isoliert. Das inklusive Verzweigungsverhältnis für den semileptonischen Zerfall des B-Mesons wird zu (10.85 +-0.22(stat.) +-0.34(sys))% gemessen. Zusammen mit der Lebenszeit von B-Mesonen lässt sich daraus |V_cb| bestimmen: |V_{cb}| = 0.0406 +-0.0009(exp) +-0.0019(theory). / An algorithm for identification of electrons with the BABAR detector is developed. Based on pure samples of electrons and hadrons obtained from data, we determine the electron identification efficiency to be above 90% for momenta above 0.5 GeV/c in the laboratory frame, while the pion fake rate lies between 0.05% and 0.1%. Based on this algorithm, a measurement of the inclusive lepton momentum spectrum in B meson decays is performed. We analyze 4.13 fb^-1 and 0.97 fb^-1 of data recorded at and slightly below the Upsilon(4S) resonance with the BABAR detector at the PEP-II a symmetric B-Factory. B-Bbar events are tagged by a high momentum electron. Using charge and angular correlations, leptons from a second semileptonic $B$ decay are separated from secondary charm semileptonic decays. The inclusive branching ratio is measured to be (10.85 +-0.22(stat.) +-0.34(sys))% . Combined with the B lifetime we determine |V_cb| = 0.0406 +-0.0009(exp) +-0.0019(theory).

The branching fraction for B -> rho e nu decays and the CKM matrix element |Vub| is measured with semileptonic exclusive B-meson decays using approximately 55 million Upsilon(4S) -> BBbar decays collected during the years 2000 and 2001 with the BABAR detector. The result is Br(B0 -> rho- e+ nu) = (3.39 +- 0.44 +- 0.52 +- 0.60) x 10^-4, and |Vub| = (3.69 +- 0.23 +- 0.27 +0.40-0.59) x 10^-3. The quoted errors are statistical, systematic, and theoretical respectively. These are combined results obtained using five different form-factor models. Individual results are also quoted. / Das Verzweigungsverhältnis B -> rho e nu und das CKM Matrix Element |Vub| werden mittels semileptonischer exklusiver B Mesonen Zerfälle gemessen. Die Daten wurden in den Jahren 2000 und 2001 mit dem BABAR Dektektor aufgezeichnet und ensprechen ungefähr 55 Millionen Upsilon(4S) -> BBbar Zerfällen. Das Ergebnis ist Br(B0 -> rho- e+ nu) = (3.39 +- 0.44 +- 0.52 +- 0.60) x 10^-4 und |Vub| = (3.69 +- 0.23 +- 0.27 +0.40-0.59) x 10^-3. Die angegebenen Fehler sind statistisch, systematisch und theoretisch. Dieses Ergebnis ist eine Kombination von Ergebnissen fünf verschiedener Form-Faktor Modelle. Die Ergebnisse werden auch für jedes Modell einzeln angegeben.

A study of the usage of ALICEs time of flight (TOF), time projection chamber (TPC), and electromagnetic calorimeter (EMCal), aiming at detecting and separating electrons and positrons (e±) originated from different sources, was carried out. To accomplish the objectives of the research, data gathered from the 2012 proton-proton (pp) collision experiment were used. At a center of mass energy of sqrt(s)=8TeV, the collision of the proton beams liberates heavy quarks, charm and bottom, with approximate lifetimes of approximately 10^13s and 10^12s, respectively. The e± generated through weak semileptonic heavy flavor decays are of interest for studying quarks, therefore it served solely as motivation and incentive for the research carried out and described herein. The introduction of carefully selected cuts, with the purpose of separating partial data collected in the three detectors, permitted the understanding of their effect on the results. Furthermore, due to the fact that the TOFs design was not meant to separate e± from the other heavier particles, only the general effects of introducing a simple cut in the beta=v/c values were analyzed. The more specific cuts were only used for the data generated by the events detected by the TPC and the EMCal. A combination of cuts based on the particles energy loss as a function of traveled distance (dE/dx), with the ratio of energy to momentum (E/p) of the particle, was adopted to enable the separation process, thus allowing for the isolation of e± from the other particles, namely pi±, K±, and p/p. The analysis was performed for values of total particle momentum in the range 0<=p<=6GeV/c. A comparison of the raw data with the results obtained by applying this procedure, indicated a substantial increase in the e± yield and efficiency, reaching average values above 90% over the entire momentum range. / Um estudo do uso dos detetores de tempo de voo (TDV), câmara de projeção de tempo (CPT), e calorímetro eletromagnético (CalEM) do ALICE, visando detectar elétrons e pósitrons (e±) originados por diferentes fontes, foi realizado. Para atingir os objetivos da pesquisa, dados coletados durante o experimento de colisões próton-próton em 2012 foram utilizados. Com um nível de enegia do centro de mass igual a raiz(s)=8TeV, a colisão dos feixes de prótons libera quarks pesados, charm e bottom, com tempo de vida de aproximadamente 10^13s e 10^12s, respectivamente. Os e± gerados pelo decaimento fraco semileptônico de sabores pesados é de interesse para o estudo dos quarks, portanto, o conceito serviu somente como motivação e incentivo para a pesquisa realizada e descrita nesta dissertação. A introdução de cortes específicos, com a finalidade de parcialmente separar dados coletados nos três detectores, permitiu adquirir entendimento sobre os efeitos do cortes nos resultados. Adicionalmente, em virtude do projeto do TDV não ter sido feito visando separar e± oriundos do decaimento dos sabores pesados das demais partículas mais massivas, somente os efeitos gerais de introduzir um corte simples nos valores de beta=v/c, foram analisados. Os cortes mais específicos foram somente nos dados detectados pelo CPT e pelo CalEM. Uma combinação de cortes baseados na perda de energia da partícula em função da distância percorrida (dE/dx), com a razão entre a energia e o momento da partícula (E/p), foi adotada para viabilizar o processo de separação, desta forma permitindo a separação dos e± das demais partículas, ou seja, dos pi±, K±, and p/p. A análise foi realizada para valores de momento total das partículas na faixa 0<=p<=6GeV/c. Uma comparação dos dados originais com os resultados obtidos pela aplicação do procedimento, indicou um aumento substancial do rendimento e eficiência dos e±, atingindo valores médios acima de 90% na faixa inteira de momento.

The Standard Model of Elementary Particle Physics (SM) is the present theoryfor the elementary particles and their interactions and is a well-established theorywithin the physics community. The SM is a combination of Quantum Chromodynamics(QCD) and the Glashow{Weinberg{Salam (GWS) electroweak model. QCDis a theory for the strong force, whereas the GWS electroweak model is a theoryfor the weak and electromagnetic forces. This means that the SM describes allfundamental forces in Nature, except for the gravitational force. However, the SMis not a nal theory and some of its problems will be discussed in this thesis.In the rst part of this thesis, several properties of baryons are studied suchas spin structure, spin polarizations, magnetic moments, weak form factors, andnucleon quark sea isospin asymmetries, using the chiral quark model (QM). TheQM is an eective chiral eld theory developed to describe low energy phenomena of baryons, since perturbative QCD is not applicable at low energies. The resultsof the QM are in good agreement with experimental data.The second part of the thesis is devoted to the concept of quantum mechanicalneutrino oscillations. Neutrino oscillations can, however, not occur within the GWSelectroweak model. Thus, this model has to be extended in some way. All studiesincluding neutrino oscillation are done within three avor neutrino oscillationmodels. Both vacuum and matter neutrino oscillations are considered. Especially,global ts to all data of candidates for neutrino oscillations are presented and alsoan analytical formalism for matter enhanced three avor neutrino oscillations usingtime evolution operators is derived. Furthermore, investigations of matter eectswhen neutrinos traverse the Earth are included.The thesis begins with an introductory review of the QM and neutrino oscillationsand ends with the research results, which are given in the nine accompanyingscientic articles. / QC 20100616

In this analysis the decay B- --&amp;gt; D*° e- nu is measured. The underlying data sample consists of about 226 million B-meson pairs accumulated on the Y(4S) resonance by the BABAR detector at the asymmetric e+e- collider PEP II. The reconstruction of the decay uses the channels D*° --&amp;gt; D° pi°, D° --&amp;gt; K- pi+ and pi° --&amp;gt; gamma gamma. The neutrino is not reconstructed. Since the rest frame of the B meson is unknown, the boost w of the D*° meson in the B meson rest frame is estimated by w'. The w' spectrum of the data is described in terms of the partial decay width dGamma/dw given by theory and the detector simulation translating each spectrum dGamma/dw into an expectation of the measured w' spectrum. dGamma/dw depends on a form factor F(w) parameterizing the strong interaction in the decay process. To find the best descriptive dGamma/dw a fit to the data determines the following two parameters of dGamma/dw: (i) F(1)|Vcb|, the product between F at zero D*°-recoil and the Quark mixing parameter |Vcb|; (ii) rho^2, a parameter of the form factor F(w). The former parameter scales the height of dGamma/dw and rho^2 varies the shape of it. The determined values of F(1)|Vcb|, rho^2 and the branching fraction BF(B- --&amp;gt; D*° e- nu) are F(1)|Vcb| = (35.8 +- 0.5 +- 1.5) x 10e-03, rho^2 = (1.08 +- 0.05 +- 0.09) and BF(B- --&amp;gt; D*° e- nu) = (5.60 +- 0.08 +- 0.42)%, where the uncertainties are statistical and systematic, respectively. The value of BF(B- --&amp;gt; D*° e- nu) has been determined by an integration of dGamma/dw over the allowed w range using the fitted values of F(1)|Vcb| and rho^2.

A study of the usage of ALICEs time of flight (TOF), time projection chamber (TPC), and electromagnetic calorimeter (EMCal), aiming at detecting and separating electrons and positrons (e±) originated from different sources, was carried out. To accomplish the objectives of the research, data gathered from the 2012 proton-proton (pp) collision experiment were used. At a center of mass energy of sqrt(s)=8TeV, the collision of the proton beams liberates heavy quarks, charm and bottom, with approximate lifetimes of approximately 10^13s and 10^12s, respectively. The e± generated through weak semileptonic heavy flavor decays are of interest for studying quarks, therefore it served solely as motivation and incentive for the research carried out and described herein. The introduction of carefully selected cuts, with the purpose of separating partial data collected in the three detectors, permitted the understanding of their effect on the results. Furthermore, due to the fact that the TOFs design was not meant to separate e± from the other heavier particles, only the general effects of introducing a simple cut in the beta=v/c values were analyzed. The more specific cuts were only used for the data generated by the events detected by the TPC and the EMCal. A combination of cuts based on the particles energy loss as a function of traveled distance (dE/dx), with the ratio of energy to momentum (E/p) of the particle, was adopted to enable the separation process, thus allowing for the isolation of e± from the other particles, namely pi±, K±, and p/p. The analysis was performed for values of total particle momentum in the range 0<=p<=6GeV/c. A comparison of the raw data with the results obtained by applying this procedure, indicated a substantial increase in the e± yield and efficiency, reaching average values above 90% over the entire momentum range. / Um estudo do uso dos detetores de tempo de voo (TDV), câmara de projeção de tempo (CPT), e calorímetro eletromagnético (CalEM) do ALICE, visando detectar elétrons e pósitrons (e±) originados por diferentes fontes, foi realizado. Para atingir os objetivos da pesquisa, dados coletados durante o experimento de colisões próton-próton em 2012 foram utilizados. Com um nível de enegia do centro de mass igual a raiz(s)=8TeV, a colisão dos feixes de prótons libera quarks pesados, charm e bottom, com tempo de vida de aproximadamente 10^13s e 10^12s, respectivamente. Os e± gerados pelo decaimento fraco semileptônico de sabores pesados é de interesse para o estudo dos quarks, portanto, o conceito serviu somente como motivação e incentivo para a pesquisa realizada e descrita nesta dissertação. A introdução de cortes específicos, com a finalidade de parcialmente separar dados coletados nos três detectores, permitiu adquirir entendimento sobre os efeitos do cortes nos resultados. Adicionalmente, em virtude do projeto do TDV não ter sido feito visando separar e± oriundos do decaimento dos sabores pesados das demais partículas mais massivas, somente os efeitos gerais de introduzir um corte simples nos valores de beta=v/c, foram analisados. Os cortes mais específicos foram somente nos dados detectados pelo CPT e pelo CalEM. Uma combinação de cortes baseados na perda de energia da partícula em função da distância percorrida (dE/dx), com a razão entre a energia e o momento da partícula (E/p), foi adotada para viabilizar o processo de separação, desta forma permitindo a separação dos e± das demais partículas, ou seja, dos pi±, K±, and p/p. A análise foi realizada para valores de momento total das partículas na faixa 0<=p<=6GeV/c. Uma comparação dos dados originais com os resultados obtidos pela aplicação do procedimento, indicou um aumento substancial do rendimento e eficiência dos e±, atingindo valores médios acima de 90% na faixa inteira de momento.

In this analysis the decay B- --&amp;gt; D*° e- nu is measured. The underlying data sample consists of about 226 million B-meson pairs accumulated on the Y(4S) resonance by the BABAR detector at the asymmetric e+e- collider PEP II. The reconstruction of the decay uses the channels D*° --&amp;gt; D° pi°, D° --&amp;gt; K- pi+ and pi° --&amp;gt; gamma gamma. The neutrino is not reconstructed. Since the rest frame of the B meson is unknown, the boost w of the D*° meson in the B meson rest frame is estimated by w'. The w' spectrum of the data is described in terms of the partial decay width dGamma/dw given by theory and the detector simulation translating each spectrum dGamma/dw into an expectation of the measured w' spectrum. dGamma/dw depends on a form factor F(w) parameterizing the strong interaction in the decay process. To find the best descriptive dGamma/dw a fit to the data determines the following two parameters of dGamma/dw: (i) F(1)|Vcb|, the product between F at zero D*°-recoil and the Quark mixing parameter |Vcb|; (ii) rho^2, a parameter of the form factor F(w). The former parameter scales the height of dGamma/dw and rho^2 varies the shape of it. The determined values of F(1)|Vcb|, rho^2 and the branching fraction BF(B- --&amp;gt; D*° e- nu) are F(1)|Vcb| = (35.8 +- 0.5 +- 1.5) x 10e-03, rho^2 = (1.08 +- 0.05 +- 0.09) and BF(B- --&amp;gt; D*° e- nu) = (5.60 +- 0.08 +- 0.42)%, where the uncertainties are statistical and systematic, respectively. The value of BF(B- --&amp;gt; D*° e- nu) has been determined by an integration of dGamma/dw over the allowed w range using the fitted values of F(1)|Vcb| and rho^2.

In dieser Dissertation wird die Suche nach schweren neutralen pseudoskalaren A und skalaren H Higgs-Bosonen vorgestellt, die in gg-Fusionen erzeugt werden, und in ein Top-Antitop-Quark-Paar zerfallen. Gesucht wurde im vollständigen Datensatz von Proton–Proton-Kollisionen bei einer Schwerpunktsenergie von 8 TeV die vom ATLAS-Detektor am Large Hadron Collider aufgezeichnet wurde und einer integrierten Luminosität von 20.3 fb−1 entspricht. Der Signalprozess und der Haupthintergrund aus der Top-Quark-Paar-Produktion über starke gg-Fusionen-Prozesse, interferieren heftig, was zu einer Verzerrung des reinen Breit-Wigner-Resonanzpeak in eine Peak-Dip-Struktur führt. Diese Analyse ist die erste am LHC, die die Interferenz zwischen Signal und Hintergrundprozessen vollständig berücksichtigt. Die Suche stützt sich auf die statistische Analyse des invarianten Top-Quark-Paar-Massenspektrum, welches aus Ereignissen mit einem Elektron oder Myon mit hohem Transversalimpuls, einer hohen fehlenden Transversalenergie von dem nicht detektierten Neutrino und mindestens vier Jets rekonstruiert wird. In den Daten wird keine signifikante Abweichung vom erwarteten Standardmodell-Hintergrund beobachtet. Die Ausschließungsgrenzen wurden abgeleitet im Kontext des Typ II Two-Higgs-Doublet Model, für Higgs-Bosonen mit einer Masse von 500 und 750 GeV und mit niedrigerem tan(\beta)-Parameter, bei der tan(\beta) das Verhältnis der Vakuumerwartungswerte der beiden Higgs-Dublett-Felder ist. Diese Parameterregionen sind weitgehend unerforscht in Untersuchungen von beliebigen Endzuständen. / In this thesis a search is presented for heavy neutral pseudoscalar A and scalar H Higgs bosons, produced in gg fusion and decaying into a top-antitop quark pair. The search is conducted on the full proton-proton collisions dataset recorded by the ATLAS detector at the Large Hadron Collider at a centre-of-mass collision energy of 8 TeV and corresponding to an integrated luminosity of 20.3 fb−1. The signal process and the main background from top quark pair production via the gg fusion strong process, interfere heavily, distorting the signal shape from the pure Breit-Wigner resonance peak to a peak-dip structure. This analysis is the first one at the LHC that fully takes into account the interference between a signal and the background processes. The search relies on the statistical analysis of the top quark pair invariant mass spectrum, which is reconstructed in signal candidate events with a high-transverse momentum electron or muon, large missing transverse energy from the undetected neutrino and at least four jets. No significant deviation from the expected SM background is observed in data. Exclusion limits are derived in the context of the type-II Two-Higgs-Doublet Model, for Higgs boson masses of 500 and 750 GeV and in the low tan(\beta) parameter region, where tan(\beta) is the ratio of the vacuum expectation values of the two Higgs doublet fields. These parameter regions have been largely unexplored by searches in any final state.