The Search for New Resonances in Strong Symmetry Breaking Scenarios with the ATLAS Detector

Utilisant les plus récentes données recueillies par le détecteur ATLAS lors de collisions pp à 7 et 8 TeV au LHC, cette thèse établira des contraintes sévères sur une multitude de modèles allant au-delà du modèle standard (MS) de la physique des particules. Plus particulièrement, deux types de particules hypothétiques, existant dans divers modèles théoriques et qui ne sont pas présentes dans le MS, seront étudiés et sondés. Le premier type étudié sera les quarks-vectoriels (QV) produits lors de collisions pp par l’entremise de couplages électrofaibles avec les quarks légers u et d. On recherchera ces QV lorsqu’ils se désintègrent en un boson W ou Z, et un quark léger. Des arguments théoriques établissent que sous certaines conditions raisonnables la production simple dominerait la production en paires des QV. La topologie particulière des évènements en production simple des QV permettra alors la mise en oeuvre de techniques d’optimisation efficaces pour leur extraction des bruits de fond électrofaibles. Le deuxième type de particules recherché sera celles qui se désintègrent en WZ lorsque ces bosons de jauges W, et Z se désintègrent leptoniquement. Les états finaux détectés par ATLAS seront par conséquent des évènements ayant trois leptons et de l’énergie transverse manquante. La distribution de la masse invariante de ces objets sera alors examinée pour déterminer la présence ou non de nouvelles résonances qui se manifesterait par un excès localisé. Malgré le fait qu’à première vue ces deux nouveaux types de particules n’ont que très peu en commun, ils ont en réalité tous deux un lien étroit avec la brisure de symétrie électrofaible. Dans plusieurs modèles théoriques, l’existence hypothétique des QV est proposé pour annuler les contributions du quark top aux corrections radiatives de la masse du Higgs du MS. Parallèlement, d’autres modèles prédisent quant à eux des résonances en WZ tout en suggérant que le Higgs est une particule composite, chambardant ainsi tout le sector Higgs du MS. Ainsi, les deux analyses présentées dans cette thèse ont un lien fondamental avec la nature même du Higgs, élargissant par le fait même nos connaissances sur l’origine de la masse intrinsèque des particules. En fin de compte, les deux analyses n’ont pas observé d’excès significatif dans leurs régions de signal respectives, ce qui permet d’établir des limites sur la section efficace de production en fonction de la masse des résonances.

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Particle acceleration and magnetic field structure in PKS 2155-304: optical polarimetric observations

In this paper, we present multiband optical polarimetric observations of the very-high energy blazar PKS 2155-304 made simultaneously with a HESS/Fermi high-energy campaign in 2008, when the source was found to be in a low state. The intense daily coverage of the data set allowed us to study in detail the temporal evolution of the emission, and we found that the particle acceleration time-scales are decoupled from the changes in the polarimetric properties of the source. We present a model in which the optical polarimetric emission originates at the polarized mm-wave core and propose an explanation for the lack of correlation between the photometric and polarimetric fluxes. The optical emission is consistent with an inhomogeneous synchrotron source in which the large-scale field is locally organized by a shock in which particle acceleration takes place. Finally, we use these optical polarimetric observations of PKS 2155-304 at a low state to propose an origin for the quiescent gamma-ray flux of the object, in an attempt to provide clues for the source of its recently established persistent TeV emission.

GLUON SATURATION AND THE FROISSART BOUND: A SIMPLE APPROACH

At very high energies we expect that the hadronic cross sections satisfy the Froissart bound, which is a well-established property of the strong interactions. In this energy regime we also expect the formation of the Color Glass Condensate, characterized by gluon saturation and a typical momentum scale: the saturation scale Q(s). In this paper we show that if a saturation window exists between the nonperturbative and perturbative regimes of Quantum Chromodynamics (QCD), the total cross sections satisfy the Froissart bound. Furthermore, we show that our approach allows us to described the high energy experimental data on pp/p (p) over bar total cross sections.

Measurement of an Excited Charmonium State and the Study of J/psi Polarization in p plus p Collisions at root s=200 GeV in PHENIX Experiment at RHIC

We report the J/psi -> e(+)e(-) and the psi` -> e(+)e(-) production cross sections in the PHENIX experiment at RHIC. The first measurements of the production cross sections of the psi` and the psi` over the J/psi, will contribute to the clarification of the theoretical understanding of the J/psi meson production. The inclusive J/psi polarization through the same decay channel is also presented, showing a trend of slightly longitudinal polarization for p(T) <5 GeV/c.

Electroweak precision constraints on the Lee-Wick standard model

We perform an analysis of the electroweak precision observables in the Lee-Wick Standard Model. The most stringent restrictions come from the S and T parameters that receive important tree level and one loop contributions. In general the model predicts a large positive S and a negative T. To reproduce the electroweak data, if all the Lee-Wick masses are of the same order, the Lee-Wick scale is of order 5 TeV. We show that it is possible to find some regions in the parameter space with a fermionic state as light as 2.4-3.5 TeV, at the price of rising all the other masses to be larger than 5-8 TeV. To obtain a light Higgs with such heavy resonances a fine-tuning of order a few per cent, at least, is needed. We also propose a simple extension of the model including a fourth generation of Standard Model fermions with their Lee-Wick partners. We show that in this case it is possible to pass the electroweak constraints with Lee-Wick fermionic masses of order 0.4-1.5 TeV and Lee-Wick gauge masses of order 3 TeV.

Calculable lepton masses, seesaw relations, and four neutrino mixings in a 3-3-1 model with an extra U(1) symmetry

We propose a scheme in which the masses of the heavier leptons obey seesaw type relations. The light lepton masses, except the electron and the electron neutrino ones, are generated by one loop level radiative corrections. We work in a version of the 3-3-1 electroweak model that predicts singlets (charged and neutral) of heavy leptons beyond the known ones. An extra U(1)(Omega) symmetry is introduced in order to avoid the light leptons getting masses at the tree level. The electron mass induces an explicit symmetry breaking at U(1)(Omega). We discuss also the mixing matrix among four neutrinos. The new energy scale required is not higher than a few TeV.

Exploring Elko typical signature

We study the prospects of observing the presence of a relatively light Elko particle as a possible dark matter candidate, by pointing out a typical signature for the process encompassing the Elko non-locality, exploring some consequences of the unusual Elko propagator behavior when analyzed outside the Elko axis of propagation. We also consider the production of a light Elko associated to missing energy and isolated leptons at the LHC, with center of mass energy of 7 and 14 TeV and total luminosity from 1 fb(-1) to 10 fb(-1). Basically, the Elko non-locality engenders a peculiar signal in the missing energy turning it sensible to the angle of detection. (C) 2011 Elsevier B.V. All rights reserved.

The Hunt for New Physics at the Large Hadron Collider

The Large Hadron Collider presents an unprecedented opportunity to probe the realm of new physics in the TeV region and shed light on some of the core unresolved issues of particle physics. These include the nature of electroweak symmetry breaking, the origin of mass, the possible constituent of cold dark matter, new sources of CP violation needed to explain the baryon excess in the universe, the possible existence of extra gauge groups and extra matter, and importantly the path Nature chooses to resolve the hierarchy problem - is it supersymmetry or extra dimensions. Many models of new physics beyond the standard model contain a hidden sector which can be probed at the LHC. Additionally, the LHC will be a. top factory and accurate measurements of the properties of the top and its rare decays will provide a window to new physics. Further, the LHC could shed light on the origin of neutralino masses if the new physics associated with their generation lies in the TeV region. Finally, the LHC is also a laboratory to test the hypothesis of TeV scale strings and D brane models. An overview of these possibilities is presented in the spirit that it will serve as a companion to the Technical Design Reports (TDRs) by the particle detector groups ATLAS and CMS to facilitate the test of the new theoretical ideas at the LHC. Which of these ideas stands the test of the LHC data will govern the course of particle physics in the subsequent decades.

Searching supersymmetry at the LHCb with displaced vertices

Supersymmetric theories with bilinear R-parity violation can give rise to the observed neutrino masses and mixings. One important feature of such models is that the lightest supersymmetric particle might have a sufficiently large lifetime to produce detached vertices. Working in the framework of supergravity models, we analyze the potential of the LHCb experiment to search for supersymmetric models exhibiting bilinear R-parity violation. We show that the LHCb experiment can probe a large fraction of the m(0)circle times m(1/2), being able to explore gluino masses up to 1.3 TeV. The LHCb discover potential for these kinds of models is similar to the ATLAS and CMS ones in the low luminosity phase of operation of the LHC.

Ximelagatran versus warfarin for prophylaxis of venous thromboembolism in major orthopedic surgery: systematic review of randomized controlled trials

INTRODUÇÃO: O ximelagatrano foi recentemente estudada para profilaxia do tromboembolismo venoso (TEV). OBJETIVO: Avaliar se o ximelagatrano comparado com a varfarina melhora a profilaxia do TEV em pacientes submetidos à cirurgia ortopédica do joelho. FONTE DE DADOS: Estudos randomizados identificados por pesquisa eletrônica na literatura médica, até 2006, cujos dados foram compilados no programa Review Manager, versão 4.2.5. RESULTADOS: Foram incluídos três estudos randomizados bem conduzidos envolvendo 4.914 participantes. Foram definidos dois sub-grupos com dosagens diferentes de ximelagatrano (24 mg and 36 mg, duas vezes ao dia). O tratamento com ximelagatrano mostrou freqüência significantemente menor de TEV que o tratamento com varfarina, mas somente na dosagem de 36-mg [risco relativo, RR 0.72 ([intervalo de confiança, IC, 95% 0.64, 0.81), p < 0.00001]. A freqüência de TEV no sub-grupo de 24-mg foi similar a da varfarina [RR 0.86 (IC 95% 0.73, 1.01), p = 0.06]. Para TEV maior, embolia pulmonar, sangramento e sangramento maior não houve diferença entre varfarina e a ximelagatrano. Ao final do tratamento, a elevação da alanino-aminotransferase (ALT) foi menos freqüente no sub-grupo de 24 mg de ximelagatrano que no grupo da varfarina [RR 0.33 (IC 95% 0.12, 0.91) p = 0.03], mas no período de acompanhamento essa elevação foi maior com 36 mg de ximelagatrano [RR 6.97 (IC 95% 1.26, 38.50) p = 0.03]. CONCLUSÃO: O ximelagatrano foi mais efetivo que a varfarina quando usado em dosagens maiores (36 mg, 2 vezes ao dia), mas às expensas de aumento de enzimas hepáticas no período de acompanhamento.

Search for B-s(0)->mu(+)mu(-) decays at D0

We report results from a search for the decay B-s(0)->mu(+)mu(-) using 1.3 fb(-1) of p (p) over bar collisions at root s = 1.96 TeV collected by the D0 experiment at the Fermilab Tevatron Collider. We find two candidate events, consistent with the expected background of 1.24 +/- 0.99, and set an upper limit on the branching fraction of B(B-s(0)->mu(+)mu(-))< 1.2x10(-7) at the 95% C.L.

Search for right-handed W bosons in top quark decay

We present a measurement of the fraction f(+) of right-handed W bosons produced in top quark decays, based on a candidate sample of t (t) over bar events in the lepton+jets decay mode. These data correspond to an integrated luminosity of 230 pb(-1), collected by the D0 detector at the Fermilab Tevatron p (p) over bar Collider at root s=1.96 TeV. We use a constrained fit to reconstruct the kinematics of the t (t) over bar and decay products, which allows for the measurement of the leptonic decay angle theta(*) for each event. By comparing the cos theta(*) distribution from the data with those for the expected background and signal for various values of f(+), we find f(+)=0.00 +/- 0.13(stat)+/- 0.07(syst). This measurement is consistent with the standard model prediction of f(+)=3.6 x 10(-4).

Extra dimensions at the CERN LHC via mini-black holes: Effective Kerr-Newman brane-world effects

We solve Einstein equations on the brane to derive the exact form of the brane-world-corrected perturbations in Kerr-Newman singularities, using Randall-Sundrum and Arkani-Hamed-Dimopoulos-Dvali (ADD) models. It is a consequence of such models that Kerr-Newman mini-black holes can be produced in LHC. We use this approach to derive a normalized correction for the Schwarzschild Myers-Perry radius of a static (4+n)-dimensional mini-black hole, using more realistic approaches arising from Kerr-Newman mini-black hole analysis. Besides, we prove that there are four Kerr-Newman black hole horizons in the brane-world scenario we use, although only the outer horizon is relevant in the physical measurable processes. Parton cross sections in LHC and Hawking temperature are also investigated as functions of Planck mass (in the LHC range 1-10 TeV), mini-black hole mass, and the number of large extra dimensions in brane-world large extra-dimensional scenarios. In this case a more realistic brane-effect-corrected formalism can achieve more precisely the effective extra-dimensional Planck mass and the number of large extra dimensions-in the Arkani-Hamed-Dimopoulos-Dvali model-or the size of the warped extra dimension-in Randall-Sundrum formalism.

Search for production of single top quarks via tcg and tug flavor-changing-neutral-current couplings

We search for the production of single top quarks via flavor-changing-neutral-current couplings of a gluon to the top quark and a charm (c) or up (u) quark. We analyze 230 pb(-1) of lepton+jets data from p (p) over tilde collisions at a center of mass energy of 1.96 TeV collected by the D0 detector at the Fermilab Tevatron Collider. We observe no significant deviation from standard model predictions, and hence set upper limits on the anomalous coupling parameters kappa(c)(g)/Lambda and kappa(u)(g)/Lambda, where kappa(g) define the strength of tcg and tug couplings, and Lambda defines the scale of new physics. The limits at 95% C.L. are kappa(c)(g)/Lambda < 0.15 TeV-1 and kappa(u)(g)/Lambda < 0.037 TeV-1.