This thesis presents a Monte Carlo study of neutral Higgs bosons of the Minimal Supersymmetric Standard Model (MSSM) decaying into muons at the Atlas experiment at the CERN Large Hadron Collider. Signal and background processes are simulated using novel Monte Carlo generators that incorporate parts of higher order corrections and are expected to give a more accurate prediction than previous programs. The SHERPA Monte Carlo generator is validated for its use in the analysis and compared to results obtained with other programs. Where possible, the Monte Carlo event samples are normalized to higher order calculations. To increase the available Monte Carlo statistics, this study is based on the ATLAS fast detector simulation ATLFAST. Differences between ATLFAST and the detailed detector simulation of ATLAS are examined, and, where possible, correction procedures are devised. A cut based analysis is performed assuming an integrated luminosity of 30 inverse femtobarns, and optimized with respect to the discovery potential for MSSM Higgs bosons. The systematic uncertainties of the event selection and the Monte Carlo predictions are estimated. A method that can be used to estimate the background from data is presented and evaluated. Last, the discovery potential of the \Atlas experiment in the CP conserving benchmark scenarios of the MSSM is evaluated. One or more of the neutral Higgs bosons of the MSSM can be discovered in the muonic decay mode using 30 inverse femtobarns of data for low masses of the pseudoscalar boson A, if the model parameter tan(beta) is at least 20. For higher masses of the A, tan(beta) would need to be significantly higher to ensure a discovery in the studied decay channel. The sensitivity of ATLAS to MSSM Higgs bosons is multiple times larger than the one of previous and currently running experiments. / Die vorliegende Arbeit präsentiert eine Monte Carlo Studie zu neutralen Higgs-Bosonen des Minimal Supersymmetrischen Standardmodells (MSSM) im myonischen Zerfallskanal am Atlas Experiment am Large Hadron Collider des CERN. Signal- und Untergrundprozesse werden mit neuartigen Monte Carlo Ereignisgeneratoren simuliert, die Teile der Korrekturen höherer Ordnung beinhalten, und von denen eine verbesserte Vorhersage erwartet wird im Vergleich zu herkömmlichen Programmen. Der SHERPA Monte Carlo Ereignisgenerator wird auf seine Brauchbarkeit für die Analyse überprüft und mit Ergebnissen anderer Programme verglichen. Sofern möglich werden die erstellten Monte Carlo Datensätze mittels Rechnungen zu höheren Ordnungen normiert. Um eine hinreichend große Statistik von simulierten Daten zu erhalten, wird die schnelle Detektorsimulation des ATLAS Detektors ATLFAST verwendet. Unterschiede zwischen der vollständigen Detektorsimulation und ATLFAST werden untersucht, und sofern möglich, Korrekturverfahren entwickelt. Eine schnittbasierte Analyse wird durchgeführt unter der Annahme einer integrierten Luminosität von 30 inversen femtobarn und optimiert mit Hinblick auf das Entdeckungspotenzial für MSSM Higgs-Bosonen. Die systematischen Unsicherheiten der Ereignisauswahl und der Monte Carlo-Vorhersagen werden abgeschätzt. Eine Methode zur Messung des Untergrundes in Daten wird vorgestellt und überprüft. Schliesslich wird das Entdeckungspotenzial des ATLAS Experiments in Vergleichspunkten für CP erhaltende Szenarien des MSSM ermittelt. F\ür niedrige Massen des pseudoskalaren Higgs-Bosons A kann mindestens eines der neutralen Higgs-Bosonen des MSSM im myonischen Zerfallskanal entdeckt werden, sofern der Modellparameter tan(beta) mindestens 20 ist. Für hohe Massen des A muss ein wesentlich größeres tan(beta) in der Natur realisiert sein, um eine Entdeckung im untersuchten Zerfallskanal zu ermöglichen. Die Sensitivität von ATLAS auf Higgs-Bosonen des MSSM ist um ein Vielfaches höher als diejenige bisheriger oder momentan laufender Experimente.

<p>Next-to-minimal super-symmetric extensions of the Standard Model (SM) predict the existence of several non-SM like Higgs bosons. The process pp→a₁h^±→4b+W involves the production and the decay of a spin-0 charged Higgs boson and a CP-odd Higgs boson a₁ which can have a sizable cross section in the NMSSM. The invariant masses of these intermediate bosons can be reconstructed from the four momenta of the final state particles using mass minimization algorithms. This thesis presents a cut-based analysis of two mass scenarios and specialized algorithms that are capable of recovering the signal in a large background arising from Standard Model processes such as ttbar. The analysis is tested with a realistic ATLAS detector simulation investigating trigger efficiencies and probing several jet reconstruction algorithms.</p>

A search for weakly interacting massive particles (WIMPs) annihilating in the Sun was performed with the IceCube and AMANDA neutrino telescopes, using data from 2008 corresponding to 149 days of livetime. Assuming that particles in the dark matter halo scatter and accumulate in the centre of the Sun, Majorana WIMPs may pair-wise annihilate and give rise to a neutrino signal detectable in an experiment at Earth. No excess of muon-neutrinos from the Sun was observed, and limits on the νμ-flux were set for masses between 50 GeV and 5 TeV considering WIMPs annihilating into b‾b and W+W-. Separate limits were also calculated for the case of the lightest Kaluza-Klein particle. The flux limits were converted to limits on the spin-dependent and spin-independent WIMP-proton cross sections, σSD and σSI. The search was combined using a joint likelihood method with AMANDA and IceCube data from 2001-2007, yielding the 90% CL upper limits Φμ &lt; 103 km-2y-1 for a WIMP mass of 1000 GeV and σSD &lt; 1.28×10-4 pb for 250 GeV, both for the W+W- spectrum. / IceCube

Next-to-minimal super-symmetric extensions of the Standard Model (SM) predict the existence of several non-SM like Higgs bosons. The process pp→a1h±→4b+W involves the production and the decay of a spin-0 charged Higgs boson and a CP-odd Higgs boson a1 which can have a sizable cross section in the NMSSM. The invariant masses of these intermediate bosons can be reconstructed from the four momenta of the final state particles using mass minimization algorithms. This thesis presents a cut-based analysis of two mass scenarios and specialized algorithms that are capable of recovering the signal in a large background arising from Standard Model processes such as ttbar. The analysis is tested with a realistic ATLAS detector simulation investigating trigger efficiencies and probing several jet reconstruction algorithms.

A search for Weakly Interacting Massive Particles (WIMPs) annihilating in the dark matter halo of the Milky Way was performed, using data from the IceCube Neutrino Observatory and its low-energy extension DeepCore. The data were collected during one year between 2011 to 2012 corresponding to 329.1 days of detector livetime. If WIMPs in the dark matter halo undergo pairwise annihilation they may produce a neutrino signal detectable at the Earth. Assuming annihilation into bb, W+W-, τ+τ-, μ+μ-, νν and a neutrino flavor ratio of 1:1:1 at the detector, cascade events from all neutrino flavors were used to search for an excess of neutrinos matching a dark matter signal spectrum. Two dark matter density profiles for the halo were used; the cored Burkert profile and the cusped NFW profile. No excess of neutrinos from the Galactic halo was observed, and upper limits were set for the thermally averaged product of the WIMP self-annihilation cross section and velocity, &lt;σAv&gt;, in the WIMP mass range 30 GeV to 10 TeV. For the bb annihilation channel and the NFW halo profile, the 90% C.L. upper limits are 9.03×10-22 cm3 s-1 for the mass WIMP 100 GeV and 4.08×10-22 cm3 s-1 for the WIMP mass 3000 GeV. The corresponding upper limits for the μ+μ- annihilation channel are 4.40×10-23 cm3 s-1 and 3.20×10-23 cm3 s-1. / IceCube

Resumo: A supersimetria é um tópico importante na física teórica atual. Em particular, tem-se dedicado grande esforço no estudo das extensões supersimétricas do Modelo Padrão (SM) desde a década de 80. A incorporação da supersimetria no SM resulta em uma grande quantidade de modelos. O modelo com o conteúdo mínimo de partículas assim como de interações é chamado o Modelo Mínimo Supersimétrico (MSSM). DEvido à supersimetria, todos os modelos supersimétricos apresentam diferenças com relação ao SM. A principal delas, além do conteúdo de partículas, está no setor de Higgs. Em particular, o setor de Higgs do modelo MSSM contem cinco graus de liberdade (cinco bósons de Higgs), diferentemente do SM, que contem apenas um bóson de Higgs. Outra diferença importante no caso do MSSM deve-se à mistura dos estados associados pela supersimetria aos bósons de Gauge e aos bósons de Higgs, chamados gauginos e higgsinos respectivamente, cujos autoestados de massa são conhecidos como charginos e neutralinos. Estas partículas desempenham um papel fundamental na possível descoberta da supersimetria na escala de energia de TeV's. / Abstract: Supersymmetry is a fundamental topic in the actual theoretical physics. In particular, since the 80's, huge efforts have been done studying the supersymmetric extensions of the Standard Model (SM). Including supersymmetry in the SM generates a great amount of models. Among all of these, there is one that involves the minimum number of particles and interactions. This model is known as the Minimal Supersymmetric Standard Model (MSSM). Due to the incorporation of supersymmetry, all the extensions have differences in relation with the SM. The most remarkable one, beyond the particles content, lies in the Higgs sector. Particularly, in the MSSM Higg's sector there are five degrees of freedom (five Higgs bosons), in contrast with the SM (just one). Another difference is related wit the higgsino and gaugino mixture. This result in the presence of mass eigenstates known as charginos and neutralinos. The later particles play a fundamental role in the possible test of supersymmetry at the TeV's scales. / Orientador: Fernando Luiz de Campos Carvalho / Coorientador: Rogério Rosenfeld / Mestre

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Submitted by Vasti Diniz (vastijpa@hotmail.com) on 2017-09-13T13:01:16Z No. of bitstreams: 1 arquivototal.pdf: 7899614 bytes, checksum: f001983854e55609b8ccfb1ce80578f2 (MD5) / Made available in DSpace on 2017-09-13T13:01:16Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 7899614 bytes, checksum: f001983854e55609b8ccfb1ce80578f2 (MD5) Previous issue date: 2015-02-27 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / One of the main problems that permeates the Particle Physics and Cosmology is the Dark Matter (DM), which makes up about 26% of the energy content of the Universe. The main evidence pointing to its existence provides us with important features, such as being neutral, stable (with lifetime over the age of the Universe), cold or warm, weakly interacting with Particle Physics Standard Model (SM) particles and sufficiently abundant. The SM does not provide a candidate who meets these characteristics and hence it is necessary to extend it. One of the most sophisticated extensions of the SM is the Supersymmetry, that in addition to solving the problem of DM, explains other unsolved puzzles that are present in SM, among them, the hierarchy and the unification of the gauge couplings. This model implies the inclusion of a new symmetry that puts bosons and fermions in equal footing. The minimal supersymmetric version of the SM is the Minimal Supersymmetric Standard Model (MSSM), whose viable candidate is the neutralino, which is a fermion composed of superpartners of neutral Higgs and gauge bosons. In this work, we performed the neutralino analysis as DM candidate in CMSSM or mSUGRA scenario, which contains 5 free parameters, M0, M1/2, tan , sign(μ) and A0, for two different analyzes. In the first one we varied the M0 and M1/2 parameters for three different values of tan while in the second and third one we varied all parameters except the sign(μ). In this study, we use some computational tools, including, SARAH, SPheno, SSP and Micromegas, in order to obtain DM Relic Abundance and DM scattering cross section in this scenario. We compared our results with the most recent experimental data, namely, we have used Planck satellite data for the relic abundance, LUX and XENON1T (prospect) for the spin-independent scattering cross section and XENON100 for the spin dependent one. We finally analyzed the implications concerning the viability of the MSSM under the light of the DM problem. / Um dos principais problemas que permeia a Física de Partículas e Cosmologia é a Matéria Escura (ME), que compõe cerca de 26% do conteúdo energético do Universo. As principais evidências que apontam para a sua existência nos fornecem importantes características, tais como, ser neutra, estável (com tempo de vida maior que a idade do Universo), fria ou morna, pouco interagente com partículas do Modelo Padrão de Física de Partículas (MP)e suficientemente abundante. O MP não fornece um candidato que supre estas características, sendo necessário estendê-lo. Uma das mais sofisticadas extensões do MP é a Supersimetria, que além de resolver o problema da ME, soluciona outros que estão presentes no MP, dentre eles, a hierarquia e a unificação dos acoplamentos de gauge. Tal modelo implica na inclusão de uma nova simetria que coloca bósons e férmions em pé de igualdade. A versão mínima supersimétrica do MP é o Modelo Padrão Supersimétrico Mínimo (MSSM), cujo candidato viável à ME é o neutralino, que se trata de um férmion composto pelos superparceiros dos bósons de gauge e Higgs neutros. Neste trabalho, fizemos uma análise do neutralino como candidato à ME no cenário CMSSM ou mSUGRA, que contém 5 parâmetros livres, M0, M1/2, tan , sinal(μ) e A0, para três análises distintas. Na primeira variamos apenas os parâmetros M0 e M1/2 para três valores distintos da tan e na segunda e terceira variamos todos os parâmetros com exceção do sinal(μ). Neste estudo, utilizamos algumas ferramentas computacionais, entre as quais, SARAH, SPheno, SSP e micrOMEGAs, no intuito de obter abundância e seção de choque de espalhamento de ME neste cenário. Obtidos os gráficos, comparamos com os resultados experimentais mais recentes, para a abundância utilizamos dados do satélite Planck, para a seção de choque de espalhamento independente de spin, o LUX e XENON1T (2017) e para dependente de spin, XENON100 e verificamos suas implicações na viabilidade do modelo.

There are experimental and theoretical indications that the Standard Model of particle physics, although tremendously successful, is not sufficient to describe the universe, even at energies well below the Planck scale. One of the most promising new theories to resolve major open questions, the Minimal Supersymmetric Standard Model, predicts additional neutral and charged Higgs bosons, among other new particles. For the search of the new heavy neutral bosons, the decay into two hadronically decaying tau leptons is especially interesting, as in large parts of the search parameter space it has the second largest branching ratio while allowing for a considerably better background rejection than the leading decay into b-quark pairs. This search, based on proton-proton collisions recorded at sqrt(s) = 13 TeV in 2015 and early 2016 by the ATLAS experiment at the Large Hadron Collider at CERN, is presented in this thesis. No significant deviation from the Standard Model expectation is observed and CLs exclusion limits are determined, both model-independent and in various MSSM benchmark scenarios. The MSSM exclusion limits are significantly stronger compared to previous searches, due to the increased collision energy and improvements of the event selection and background estimation techniques. The upper limit on tan beta at 95% confidence level in the mhmod+ MSSM benchmark scenario ranges from 10 at mA = 300 GeV to 48 at mA = 1.2 TeV.

The search for additional heavy neutral Higgs bosons predicted in Minimal Supersymmetric Extensions of the Standard Model is presented, using the direct decay channel into two tau leptons which themselves decay hadronically. The study is based on proton-proton collisions recorded in 2011 at a center-of-mass energy of 7 TeV with the ATLAS detector at the Large Hadron Collider at CERN. With a sample size corresponding to an integrated luminosity of 4.5 fb−1, no significant excess above the expected Standard Model background prediction is observed and CLs exclusion limits at a 95% confidence level are evaluated for values of the CP-odd Higgs boson mass mA between 140 GeV to 800 GeV within the context of the mhmax and mhmod± benchmark scenarios. The results are combined with searches for neutral Higgs bosons performed using proton-proton collisions at a center-of-mass energy of 8 TeV recorded with the ATLAS detector in 2012, with a corresponding integrated luminosity of 19.5 fb−1. The combination allowed an improvement of the exclusion limit at the order of 1 to 3 units in tan β. Within the context of this study, the structure of additional interactions during a single proton-proton collision (the “underlying event”) in di-jet final states is analyzed using collision data at a center-of-mass energy of 7 TeV recorded with the ATLAS detector in 2010, with a corresponding integrated luminosity of 37 pb−1. The contribution of the underlying event is measured up to an energy scale of 800 GeV and compared to the predictions of various models. For several models, significant deviations compared to the measurements are found and the results are provided for the optimization of simulation algorithms.