Ce mémoire présente une synthèse des travaux que j'ai effectués depuis 7 ans pour la préparation de l'expérience ATLAS, devant fonctionner auprès du futur grand collisionneur de hadrons du CERN, le LHC, qui entrera en service en 2008.

Heavy ions are collided at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL) in an effort to create a unique state of nuclear matter, where quarks and gluons can freely move over volumes larger than the typical size of a nucleon (typical scale of Quantum Chromodynamics, QCD). In this state, called a "Quark Gluon Plasma" (QGP), it is proposed Chiral symmetry is restored. The fact that Chiral symmetry is a symmetry of the Standard model and is broken at low energy (current energy scale of universe) makes the study of its possible very interesting. The analysis in this dissertation searches for signatures of chiral symmetry restoration at the phase transition between the QGP and the hadronic gas phase by using resonance particles as probes. Resonances may decay inside of hot dense matter due to their short lifetimes, and therefore their decay daughters carry away dynamical information such as the mass and decay width. Mass shift and width broadening are predicted signatures of chiral symmetry restoration. The [phi](1020) resonances reconstructed from the dielectron decay channel are investigated in this dissertation. This decay channel does not suffer scattering from the late hadronic medium due to the relatively small interaction cross section of leptons with hadrons. The disadvantage of this channel comes from the small branching ratio. Therefore, large statistics and clean Particle IDentification (PID) are necessary for this analysis. Those requirements were fulfilled with high luminosity beams at RHIC and the newly developed and installed Time Of Flight (TOF) detectors, which provide clear particle identification up to momentum of 2-3 GeV/c, as well as the large acceptance of the Solenoidal Tracker At RHIC (STAR) detector. In this dissertation, measurements of mass, width, transverse momentum spectrum, and yields of [phi][right arrow] e⁺e⁻ at mid-rapidity [mathematical symbols] from the STAR experiment in Au+Au collisions at [mathematical symbols]=200 GeV are presented and compared to a previously measured [phi] meson result from a hadronic decay channel. The possibility of medium modification which implies Chiral symmetry restoration is discussed. / text

This work aims to understand how cosmic inflation embeds into larger models of particle physics and string theory. Our work operates within a weakened version of the Landscape paradigm, wherein it is assumed that the set of possible Lagrangians is vast enough to admit the notion of a generic model. By focusing on slow-roll inflation, we examine the roles of both the scalar potential and the space of couplings which determine its precise form. In particular, we focus on the structural properties of the scalar potential, and find a surprising result: inflection point inflation emerges as an important —and under certain assumptions, dominant — possibility in the context of generic scalar potentials. We begin by a systematic coarse graining over the set of possible inflection point inflation models using V.I. Arnold’s ADE classification of singularities. Similar to du Val’s pioneering work on surface singularities, these determine structural classes for inflection point inflation which depened on a distinct number of control parameters. We consider both single and multifield inflation, and show how the various structural classes embed within each other. We also show how such control parameters influence the larger physical models in to which inflation is embedded. These techniques are then applied to both MSSM inflation and KKLT-type models of string cosmology. In the former case, we find that the scale of inflation can be entirely encoded within the super- potential of supersymmetric quantum field theories. We show how this relieves the fine-tuning required in such models by upwards of twelve orders of magnitude. Moreover, unnatural tuning between SUSY breaking and SUSY preserving sectors is eliminated without the explicit need for any hidden sector dynamics. In the later case, we discuss how structural stability vastly generalizes — and addresses — the Kallosh-Linde problem. Implications for the spectrum of SUSY breaking soft terms are then discussed, with an emphasis on how they may assist in constraining the inflationary scalar potential. We then pivot to a general discussion of the FLRW-scalar phase space, and show how inflection points induce caustics — or dynamical fixed points — amongst the space of possible trajectories. These fixed points are then used to argue that for uninformative priors on the space of couplings, the likelihood of inflection point inflation scales with the inverse cube of the number of e-foldings. We point out the geometric origin for the known ambiguity in the Liouville measure, and demonstrate of inflection point inflation ameliorates this problem. Finally we investigate the effect of the fixed point structure on the spectrum of density perturbations. We show how an anomaly in the Cosmic Mircowave Background data — low power at large scales — can be explained as a by product of the fixed point dynamics.

One of the primary goals of the CERN Large Hadron Collider is to search for new physics. Many such searches have been carried out, in particular searches for supersymmetry, yet no new physics beyond the Standard Model has been found. With a large number of free parameters introduced by frameworks such as supersymmetry, it can be difficult to interpret the null results of searches. The first analysis presented in this thesis attempts to tackle this difficulty head-on, and gives a summary of the constraints from the Run-1 ATLAS searches. A combination of 22 searches were used, with integrated luminosities of up to 20.3 inverse femtobarns of 7 and 8 TeV data. The results are interpreted in the context of the 19-dimensional phenomenological MSSM, and are presented in terms of the masses of supersymmetric particles. Constraints from dark matter, heavy flavour and precision electroweak measurements were incorporated, and results are also interpreted in terms of these observables. Properties of models missed by the Run-1 searches are also shown. The second analysis presented in this thesis documents a direct search for new physics, using 18.2 inverse femtobarns of 13 TeV data collected during 2015 and 2016 by the ATLAS detector. The search targets final states with large jet multiplicity (at least 7 to at least 10 jets), which can arise from the pair production of gluinos decaying via a cascade. Further requirements are imposed on the sum of masses of reclustered large-radius jets. No evidence for new physics is found, and the results are interpreted in both a model-independent way and in terms of two simplified supersymmetric models, one of which was inspired by the results of the first study. Limits on the gluino mass of up to 1600 GeV are set at the 95 % confidence level, extending previous limits.

<p> In this dissertation we study properties of superconformal field theories (SCFTs) that arise from a variety of constructions. We begin with an extended review of various techniques in supersymmetry that are relevant throughout the work. In Chapter 3, we discuss aspects of theories with superpotentials given by Arnold's <i>A,D,E</i> singularities, particularly the novelties that arise when the fields are matrices. We focus on four-dimensional <i> N</i> = 1 variants of supersymmetric QCD, with <i>U</i>(<i> N_c</i>) or <i>SU</i>(<i>N_c</i>) gauge group, <i>N_f</i> fundamental flavors, and adjoint matter fields <i>X</i> and <i>Y</i> appearing in <i> W_A,D,E</i>(<i>X,Y</i>) superpotentials. We explore these issues by considering various deformations of the <i>W_A,D,E</i> superpotentials, and the resulting RG flows and IR theories. In Chapter 4, we examine the infrared fixed points of four-dimensional <i> N</i> = 1 supersymmetric <i>SU</i>(2) gauge theory coupled to an adjoint and two fundamental chiral multiplets. We focus on a particular RG flow that leads to the <i>N</i> = 2 Argyres-Douglas theory <i> H</i>₀, and a further deformation to an <i>N</i> = 1 SCFT with low <i>a</i> central charge. Then for the latter half of the dissertation we turn our attention to 4d SCFTs that arise from compactifications of M5-branes. In Chapter 6, we field-theoretically construct 4d <i>N </i> = 1 quantum field theories by compactifying the 6d (2,0) theories on a Riemann surface with genus <i>g</i> and <i>n</i> punctures, where the normal bundle decomposes into a sum of two line bundles with possibly negative degrees <i>p</i> and <i>q</i>. In Chapter 7, we study the 't Hooft anomalies of the SCFTs that arise from these compactifications. In general there are two independent contributions to the anomalies: there is a bulk term obtained by integrating the anomaly polynomial of the world-volume theory on the M5-branes over the Riemann surface, and there is a set of contributions due to local data at the punctures. Using anomaly inflow in M-theory, we describe how this general structure arises for cases when the four-dimensional theories preserve <i>N</i> = 2 supersymmetry, and derive terms that account for the local data at the punctures.</p><p>

O experimento SELEX-E781, no Fermilab, coletou 15 bilhões de interações hadrônicas durante os 18 meses de tomada de dados, (Fevereiro-96 a Setembro 97), usando um feixe secundário de 600 GeV/c, composto 50 % - e 50% - e feixe de prótons a 500 GeV/c em alvos de cobre e carbono, com o propósito de estudar a produção e decaimentos de partículas contendo o quark charme. Neste trabalho são apresentados resultados da produção inclusiva do bárion charmoso \'A IND.C\'+ e anti-bárion \'A IND.C\'- decaindo em \'A IND.C\' pK. Mais especificamente, medem-se os parâmetros resul- tantes dos ajustes das distribuições corrigidas do \'A IND.C\'+ e estado conjugado de carga, em função das variáveis cinemáticas, xF e o quadrado do momento transversal (\'p POT.2\'), por funções fenome- nológicas conhecidas na literatura. Uma amostra de 2500 ± 90 \'A IND.C\'\'s (e conjugado de carga) foi extraída após a aplicação de todos os critérios de seleção de eventos. São feitas discussões sobre relações entre os números quânticos de sabor do feixe e da partícula produzida. Grandes valores de assimetrias entre \'A IND.C\'+ e \'A IND.C\'- em função do momento longitudinal, são medi- dos para feixes de bárions enquanto que um pequeno valor e encontrado para o feixe de mé- sons. Os dados, quando possível, são também comparados a outras medidas realizadas em experimentos de hadroprodução anteriores. / The SELEX experiment at Fermilab took data during 18 months (February 96 - September 97) and collected approximately 15 billion hadronic interactions, using a 600 GeV/c secondary beam with equal amounts of - and - and 500 GeV/c próton beam on copper and carbon tar gets to study the production and decay of particles containing a charm quark. In this work results are presented on the inclusive production of the Ac+ and Ac- charm baryon where the Ac is reconstructed from its decay into pK. Specifically, we extract parameters of phenomenological models from fits to the acceptance corrected distributions of the Ac+ and charge conjugate, as a function of kinematic variables such as scaled longitudinal momentum (xF ) and transference moment squared (p2t ). A sample of 2500 ± 90 cs (and charge conjugate) was extracted in the course of the selection criteria. Correlations between the flavor quantum number of the beam and the produced particle are discussed. Large values of the asymmetry between Ac+ and Ac- as a function of xF, are obtained for baryon beam. In contrast, small asymmetry is found for the pion beam. The results are also compared to previous measurements by other experiments which used a - and - beam

The ATLAS Experiment at the CERN Large Hadron Collider is a particle physics experiment to study fundamental particles and their interactions at very high energies. Supersymmetry is a theory of new physics beyond the Standard Model of particle physics. A search for directly produced pairs of the supersymmetric partner of the top quark was performed using 20 fb^-1 of proton--proton collision data at a centre of mass energy of 8 TeV taken in 2012. The search targeted a model where the supersymmetric partner of the top quark (``scalar top'') decays via the supersymmetric partner of the tau lepton (``scalar tau'') into the supersymmetric partner of the graviton (``gravitino''). Scalar top candidates were searched for in pp collision events with either two hadronically decaying taus, two light leptons (electrons or muons), or one hadronically decaying tau and one light lepton. The numbers of events passing the analysis selection criteria agree with the Standard Model expectations. Exclusion limits at the 95% confidence level were set as a function of the scalar top and scalar tau masses. Depending on the scalar tau mass, ranging from the 87 GeV limit set by the LEP experiments to a few GeV below the scalar top mass, lower limits between 490 GeV and 640 GeV were placed on the scalar top mass within the model considered. / Graduate

A search for resonance signals from new physics models was performed using the ATLAS dijet invariant mass spectrum at a center-of-mass energy of 8 TeV. The full dataset from the 2012 data-taking period was used, corresponding to an integrated luminosity of 20.3 fb⁻¹. The analysis covered a mass range from 250 GeV to 4.5 TeV and found no evidence of an excess anywhere in the spectrum. Upper mass limits were set at 95% CL on both model- specific benchmark new physics signals and on two different generic resonance forms: a Gaussian shape and a Breit-Wigner shape which accounted for pdf and detector effects. The analysis excluded excited quarks below 4.06, heavy <i>W'</i> bosons below 2.45, colour-octet scalars below 2.70, leptophobic chiral excited bosons <i>W^*</i> below 1.75, and quantum black holes below 5.66 and 5.62 for the Qbh and BlackMax generators respectively.

According to the Big Bang Theory, matter and antimatter were produced in equal amounts at the beginning. Over time the antimatter disappeared, leaving galactic struc- tures composed only of matter. Therefore, there is some process in nature that proceeds at different rates for matter and antimatter due to the violation of the CP symmetry. CP violation has been observed in strange and bottom quark meson decays. However, a direct CP violation is predicted in the τ lepton sector. Specifically, the charge asymmetry due to CP violation in the decay τ − → π−K0S (≥ 0π0) ντ is predicted to be (+0.33 ± 0.01)%. In this work the charge asymmetry of the decay τ − → π−K0S (≥ 0π0) ντ is measured using a dataset of 437 million τ lepton pairs collected by the BABAR experiment at the SLAC Na- tional Accelerator Laboratory. The charge asymmetry induced by CP violation is found to be A = (−0.45 ± 0.24 ± 0.11) %, consistent with prediction. / Graduate

To explore the feasibility of processing Compact Muon Solenoid (CMS) analysis jobs across the wide area network, the FIU CMS Tier-3 center and the Florida CMS Tier-2 center designed a remote data access strategy. A Kerberized Lustre test bed was installed at the Tier-2 with the design to provide storage resources to private-facing worker nodes at the Tier-3. However, the Kerberos security layer is not capable of authenticating resources behind a private network. As a remedy, an xrootd server on a public-facing node at the Tier-3 was installed to export the file system to the private-facing worker nodes. We report the performance of CMS analysis jobs processed by the Tier-3 worker nodes accessing data from a Kerberized Lustre file. The processing performance of this configuration is benchmarked against a direct connection to the Lustre file system, and separately, where the xrootd server is near the Lustre file system.