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The hadronic decay D0 → KS pi+ pi- provides direct access to the measurement of the mixing parameters of the neutral charm meson system and allows to test for indirect CP violation. Mixing is a time-dependent phenomenon for which the time evolution of the transition amplitude of a D0 (anti-D0) decay to the final state KS pi+ pi- has to be considered. The parameters driving those time-dependent oscillations are x and y, depending on the masses and widths of the physical eigenstates. The CP violation parameters |q/p| and phi describe the superposition of the flavour eigenstates D0 and anti-D0 and of the physical eigenstates D1 and D2. By measuring the time- and phase-space dependent distribution of D0 → KS pi+ pi- decays, the mixing parameters can be extracted and a search for indirect CP violation can be performed. This thesis reports a measurement of the mixing parameters and the preparations of a measurement of the CP violation parameters on data collected with the LHCb experiment in 2011 and 2012, corresponding to an integrated luminosity of 3/fb. The D0 and anti-D0 mesons are required to originate from a semileptonic decay of a B meson. The parameters of interest are extracted from a fit in D0 decay time and the Dalitz variables. The phase-space distribution of D0 → KS pi+ pi- decays is modelled by expressing the three-body decay as a succession of two-body decays. The decay amplitude of a D0 or anti-D0 meson into KS pi+ pi- final state is a superposition of all possible intermediate resonances and the single resonances interfere with each other across the phase-space.

[pt] A partir do século passado descobrimos a existência de antipartículas e, desde então, a busca por entender a assimetria entre partícula e antipartículas tem sido um forte campo de pesquisa na física. Dentre as condições que possibilitam a assimetria matéria-antimatéria no Universo, está o fenômeno da Violação de Carga-Paridade (VCP). Devido à ela observamos diferenças entre os processos decaimento de uma partícula e sua antipartícula. Tal fenômeno tem efeitos importantes para mésons formados pelos quarks b ou s, porém as predições deste efeito para o setor de charme são muito pequenas, com assimetrias de CP em torno da ordem de 10−3 ou menores. De fato, apenas recentemente a VCP foi observada em decaimentos de 2 corpos de mésons D0. Esta dissertação discute duas estratégias na busca por VCP no canal D+ → π−π+π+ utilizando dados do experimento LHCb durante o Run II. O método de busca por VCP, método Mirandizing, consiste em computar estatisticamente as populações de D+ e D− em intervalos do espaço de fase bidimensional, calculando a significância da diferença dessas populações. Para amostras de grande estatística, como é o nosso caso, o objetivo final é aplicar um método alternativo que consiste em obter o número das populações através de ajustes de massa para cada intervalo. Este trabalho tem como objetivo realizar a validação do método. Nossa estratégia é realizar os procedimentos dividindo a amostra de forma aleatória em duas sub-amostras e não separando nas amostras de D+ e D−. O que se espera, então, são resultados que demonstrem compatibilidade estatística entre as duas amostras. Além dessa validação utilizando os dados, vamos, também, realizar o mesmo procedimento em 100 pseudo-experimentos. Adicionalmente, realizamos os estudos de sensibilidade a fim de verificar em quais possíveis cenários a VCP poderia ser observada nesse canal, dado o tamanho da amostra total. Para este estudo, obteremos o número das populações através da contagem direta (método Mirandizing) dos eventos do espaço de fase dentro da região de massa de maior com maior concentração de eventos de sinal. / [en] Last century we discovered the existence of antiparticles, and since then the search to understand the asymmetry between particles and antiparticles has been a strong field of research in physics. Among the conditions that make matter-antimatter asymmetry possible in the Universe is the Charge-Parity Violation (CPV) phenomenon. Due to it we observe differences between the decay processes of a particle and its antiparticle. Such a phenomenon has important effects for mesons formed by b or s quarks, but the predictions of this effect for the charm sector are very small, with CP asymmetries around the order of 10−3 or smaller. In fact only recently has CPV been observed in 2-body decays of D0 mesons. This dissertation presents the validation of strategies in the search for CPV in the D+ → π−π+π+ channel using data from the LHCb experiment during Run II. The CPV search method, the so-called Mirandizing method, consists of statistically computing the populations of D+ and D− in intervals of the two-dimensional phase space, obtaining the significance of the difference of these populations. For large statistical samples, as is our case, the ultimate goal is to apply an alternative method by obtaining the number of the populations through mass fits for each interval. This work aims to perform the validation of the method. Our strategy is to perform the procedure by dividing the sample randomly into two subsamples, but not separating into the D+ and D− samples. What is expected, then, is that the results demonstrate statistical compatibility between the two samples. In addition to this validation using data, we will also perform the same procedure on 100 pseudo-experiments. Finally, we perform sensitivity studies in order to verify the possible scenarios in which CPV could be observed in this channel, given the total sample size. For this study, we will obtain the number of the populations by directly counting the phase space events (Mirandizing) within the mass region with the highest concentration of signal events.

A central goal of flavour physics is a precise determination of the elements of the CKM matrix, which quantifies the strength of charged-current weak interactions between quarks. Of particular interest is the angle γ in the 'b-d' unitarity triangle parameterisation of the CKM matrix. One of the most promising methods to determine γ directly is to measure CP violation in interfering B±->DK± decays, where D indicates a coherent superposition of D0 and D0bar, both of which decay to the same final state. When using this method it is essential to determine the hadronic decay parameters of the D precisely in order to reduce the systematic uncertainties on the measurement of γ. One such parameter is the strong-phase difference between D0 and D0bar decays, which must be accurately known across the entire kinematic phase space. In this thesis we present measurements related to the determination of γ at both the CLEO-c experiment at Cornell University and the LHCb experiment at CERN. Firstly, we describe a model-independent determination of the D->KsKK strong-phase difference using 818pb-1 of quantum-correlated D0-D0bar data collected by CLEO-c at the ψ(3770) resonance. We reconstruct D->KsKK decays tagged with a variety of final states. By studying these decays we determine the weighted cosine and sine of the strong-phase difference in bins across the Dalitz plane. We run simulations to estimate the impact of these measurements on a determination of γ using B±->D(KsKK)K± decays. The resulting uncertainty on γ due to the CLEO-c inputs is between 3.2° and 3.9°, depending on how the Dalitz plane is binned. Furthermore, we present a model-independent measurement of the CP content of the decay D0->KsKK in the kinematic region of the φ->KK resonance. The fraction of CP-odd events in this region is 0.76 or higher at the 90% C.L. We also present an analysis of data recorded by LHCb in 2010, corresponding to an integrated luminosity of 36.5pb-1. We reconstruct the decays B±->D(Kπ)h± and B±->D(KK)h±, where h± indicates either K± or π±. Although there are not enough events in this dataset to measure γ, we are able to measure other observables related to CP violation in the B±->Dh± system. We measure B(DK,Fav)/B(Dπ,Fav), the ratio of the branching fraction of B±->D(Kπ)K± to that of B±->D(Kπ)π±, to be 0.066 ± 0.005 ± 0.004, and B(DK,CP)/B(Dπ,CP), the ratio of the branching fraction of B±->D(KK)K± to that of B±->D(KK)π±, to be 0.093 ± 0.019 ± 0.005. We determine several CP asymmetries: A(CP+,DK), the CP asymmetry in B±->D(KK)K± decays, is measured as 0.06 ± 0.17 ± 0.07; A(CP+,Dπ), the CP asymmetry in B±->D(KK)π± decays, is found to be 0.009 ± 0.042 ± 0.011; and A(Fav,DK), the CP asymmetry in B±->D(Kπ)K± decays, is measured as -0.109 ± 0.085 ± 0.019. Finally we calculate R(CP+), the ratio of the branching fraction of B±->D(KK)K± to that of B±->D(Kπ)K±, to be 1.41 ± 0.31 ± 0.11. These results indicate that LHCb is in a strong position to make a world-leading measurement of γ with a larger data sample.

This thesis documents two studies of the neutral charm meson system using the LHCb detector, and gives an overview of the numerous changes made to the LHCb software trigger in advance of Run 2 of the LHC. In the first analysis, amplitude models are applied to studies of the resonance structure in D⁰ → K⁰_SK^−π⁺ and D⁰ → K⁰_SK⁺π^− decays using proton-proton collision data, corresponding to an integrated luminosity of 3.0 fb^−1, collected during Run 1 of the LHC. Relative magnitude and phase information is determined, and coherence factors and related observables are computed for both the whole phase space and a restricted region of 100 MeV/c² around the K*(892)^± resonance. Two formulations for the Kπ S-wave are used, both of which give a good description of the data. The ratio of branching fractions B (D⁰→ K⁰_SK⁺π^−) /B (D⁰→ K⁰_SK^−π⁺) is measured to be 0.655 ± 0.004 (stat) ± 0.006 (syst) over the full phase space and 0.370 ± 0.003 (stat) ± 0.012 (syst) in the restricted region. A search for CP violation is performed using the amplitude models and no significant effect is found. Predictions from SU(3) flavour symmetry for K*(892)K amplitudes of different charges are compared with the amplitude model results, and marginal agreement is found. The second study estimates the sensitivity to D⁰–D⁰ mixing and indirect CP violation parameters that can be achieved using a model-independent technique and the samples of D⁰→ K⁰_SK⁺K^− decays recorded by LHCb in Run 1 and Run 2 of the LHC. These studies show that constraints on these parameters could be significantly improved by an analysis of the anticipated Run 2 dataset.

This thesis presents two measurements made using data collected by the LHCb detector, operating at the Large Hadron Collider accelerator at the CERN particle physics laboratory. The first is a measurement of the production rates of promptly produced D0, D+, Ds+, and D*+ open charm mesons, using data collected in 2015 at a proton-proton centre-of-mass energy of √s = 13 TeV. The second is a search for direct CP violation in two three-body decays of the Lambda_c charm baryon, pKK and ppipi, using data collected in 2011 at √s = 7 TeV and in 2012 at √s = 8 TeV. For each measurement, motivation and context are given from the standpoint of improving the theoretical understanding of the Standard Model and searching for signs of physics that cannot be explained by it, and then the various statistical analysis techniques used to extract physical quantities from the data are explained. The systematic limitations of the method are explored and quantified, and then the results are presented.

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No description available.

[pt] O Modelo Padrão (SM) da física de partículas é atualmente a melhor teoria para descrever as interações entre partículas elementares e suas propriedades. A observação da violação do CP em diversos processos fracos no setor de quarks - permitindo uma distinção absoluta entre partículas e antipartículas - é bem explicada pelo SM (através do chamado Cabibbo-Kobayashi-Maskawa ansatz). A violação do CP é uma das condições necessárias para a bariogênese e pode ser a chave para explicar a assimetria matéria-antimatéria no universo. Esta dissertação apresenta a busca por violação de CP no decaimento D+ → π−π+K+ duplamente suprimido por Cabibbo (DCS), usando dados coletados pelo LHCb de 2016-2018 de colisões pp com uma energia de centro de massa de 13 TeV, correspondendo a uma luminosidade integrada de 5,6 fb1. O objetivo desta análise é a implementação de uma técnica independente de modelo para realizar uma comparação estatística entre o espaço de fase, denominado Dalitz Plot (DP), de partícula e antipartícula no canal de decaimento, buscando diferenças locais na distribuição de eventos entre os dois DPs. Primeiro, foi feito um processo de seleção para remover contribuições de background de outros decaimentos de charme, bem como uma análise multivariada utilizando algoritmos de aprendizado de máquina para reduzir os níveis de background combinatoriais. Após a seleção, foi obtida uma amostra final 6M de candidatos a sinal, que é hoje a maior amostra já obtida para um canal de decaimento D+ DCS, permitindo uma excelente sensibilidade para busca de VCP. Essa é a primeira busca de VCP no canal de decaimento estudado. Esta análise é realizada de forma cega, o que significa que não há resultado para a região do sinal nesta primeira etapa e, para garantir que não haja assimetrias espúrias, como efeitos de produção e detecção, foram realizados testes para a região de background, para o canal de controle D+ → K−π+π+ e para a amostra simulada de Monte Carlo. / [en] The Standard Model (SM) of particle physics is currently the best theory to describe the interactions between elementary particles and their properties. The observation of CP violation in a variety of weak processes in the quark sector — allowing an absolute distinction of particles and antiparticles — is well explained by the SM (through so-called Cabibbo-Kobayashi-Maskawa ansatz). CP violation is one of the necessary conditions for baryogenesis and might be the key to explain the matter-antimatter asymmetry in the universe. This dissertation presents the search for CP violation in the doubly Cabibbo suppressed (DCS) D+ → π−π+K+ decay, using data collected by LHCb from 2016-2018 of pp collisions with a centre of mass energy of 13 TeV, corresponding to an integrated luminosity of 5.6 fb1. The goal of this analysis is the implementation of a model-independent technique to perform a statistical comparison between the phase space, called Dalitz Plot (DP), of particle and antiparticle decay channel, searching for local differences in the distribution of events between the two DPs. First, a selection process was executed to remove background contributions from other charm decays, as well as a multivariate analysis using machine learning algorithms to reduce combinatorial background levels. After the selection, a final sample of ¨6M signal candidates was obtained, which is nowadays the largest sample ever obtained for a DCS D+ decay channel, allowing an outstanding sensitivity for CPV search. This is the first CPV search in the studied decay channel. This analysis is performed blinded, meaning that there is no actual result for the signal region at this first stage and in order to guarantee that there are no nuisance asymmetries, from production and detection effects, tests were performed using the background region, the control channel D+ → K−π+π+ and the Monte Carlo simulated sample.

[pt] Na última década, desde o início do funcionamento do LHC, o Modelo Padrão de física de partículas vem sendo posto à prova com precisão sem precedentes, com enorme êxito. Um de seus experimentos é o LHCb, dedicado à física dos hádrons contendo os quarks beauty e charm. Um dos importantes temas de pesquisa do LHCb é o estudo de efeitos de assimetria partícula-antipartícula em processos de decaimento, devido à chamada violação de Carga-Paridade (CP). A violação de CP é prevista pelo Modelo Padrão e, em decaimentos envolvendo o quark charm, pode ocorrer em certos processos chamados de suprimidos por Cabibbo. No entanto, este efeito é muito pequeno, da ordem de 0.1 porcento. Esta pequenez faz com que o ambiente de decaimentos charmosos seja atraente para busca por física além do Modelo Padrão. O objetivo deste trabalho é o estudo de sensibilidade para violação de CP nos canais D+ -> K- K+π+ e D+ -> π- π+π+: no run II do LHCb. Através de uma representação do espaço de fase desses decaimentos, chamado de Dalitz Plot, e a utilização do método de Mirandizing, que se baseia em procurar significâncias locais na diferença da distribuição de eventos no Dalitz Plot de partícula e antipartícula, pode-se buscar por assimetrias de carga que indicariam efeitos de violação de CP nestes decaimentos. Baseando-se nas estatísticas dos dados tomados entre 2016 e 2018 no LHCb, foram desenvolvidos pseudoexperimentos, via método de Monte Carlo, visando reproduzir a dinâmica dos dados reais, e inserindo pequenos efeitos de violação de CP. Verificamos que há sensibilidade para a violação de CP com efeitos da ordem de 10-3 em algumas situações, que condiz com as expectativas do Modelo Padrão, o que indica a possibilidade de observação de violação de CP nos dados reais do run II. / [en] In the last decade, since the beginning of the operation of the LHC, the Standard Model of particle physics has been tested with unprecedented precision, with enormous success. One of its experiment is LHCb, dedicated to the physics of hadrons containing the beauty and charm quarks. One of the important research topics of the LHCb is the study of the effects of particle-antiparticle asymmetry in decay processes, due to the so-called charge-parity violation (CP). CP violation is predicted by the Standard Model and, in decays involving the charm quark, it can occur in certain processes called Cabibbo-suppressed. However, this effect is very small, of the order of 0.1 percent. This smallness makes the environment of charm decays attractive to search for physics beyond the Standard Model. The aim of this work is the study of sensitivity for CP violation in the channels D+ -> K-K+π+ and D+ -> π-π+π+ in run II of the LHCb. Through the phase space of these decays, called Dalitz Plot, and the use of the Mirandizing method, which is based on looking for local significance in the difference in the distribution of events for particle and antiparticle Dalitz Plots, one can seek for local asymmetries that would indicate effects of CP violation in these decays. Based on the data statistics taken between 2016 and 2018 at the LHCb, pseudo experiments were performed, using the Monte Carlo method, aiming to reproduce the dynamics of real data, and inserting small effects of CP violation. We found that there is sensitivity for CP violation with effects of the order of 10−3 in some situations, which is the expected level predicted by the Standard Model, indicating a possibility for observing CP violation in the real data from run II.