Some important aspects of pion propagation in hot and dense nuclear matter are investigated by considering the dominant p-wave pion nucleon interaction including the $ Delta$-isobar channel. We find that for zero temperature nuclear mater, the static approximation in the computation of the pion branch dispersion relation is not adequate in general. In the finite temperature nuclear matter up to T = 50MeV, the pion propagation does not change much comparing to that in the zero temperature medium, but the pion absorption through the first order pion-nucleon interaction, on the other hand, increases significantly as the temperature goes up. We also give a formula to determine the critical nuclear matter density $ rho sb{c}$ and when $ rho > rho sb{c}$ is satisfied, a minimum exists in the corresponding pion branch.

<p> According to the Standard Model of particle physics, elementary particles interact via the exchange of mediator particles. The specific mediator particle depends on the force: gluons for the strong nuclear force, photons for the electromagnetic force, and W and Z bosons for the weak nuclear force. No quantum theory of gravity has been deemed adequate by the community at this time, and no gravity-mediating particle (graviton is the proposed name for such a particle) is included in the Standard Model. As gravity is much weaker than the other fundamental forces at the particle level, this does not currently pose practical difficulties for elementary particle physics. In order to specifically study W and Z bosons, it is necessary to generate high-energy beams of particles, which are collided, and whose collisions (hopefully) produce the 90 GeV required for Z boson production. Typically, electrons and protons are the particle of choice for these beams. In order to obtain the necessary energies, circular collider facilities have been the highest energy sites for years. As electrons radiate energy when in circular orbits, by the late 1980's proton colliders have been the primary choice for high-energy physics. One such collider, built at Fermilab National Accelerator Laboratory in Batavia, Illinois, was the Tevatron, which started operations in 1984 and finally shut down in 2011. The Tevatron collided protons with anti-protons with a center of mass energy of 1.96 TeV for ten years (2001-2011) after a series of upgrades known collectively as Run II. Of the two detectors at the Tevatron, this analysis considers events observed at the Collider Detector at Fermilab (CDF) during Run II. Results can be usefully cross-checked by the other detector, D0. This thesis includes a technical description of the silicon tracking system at the CDF detector, including an account of challenges encountered during its operation and some of the personal work done to assist in its continuing operation. This analysis measures the frequency at which two bosons are created (specifically, a photon and a Z boson) in a particular decay channel (namely, the Z decays into two b quarks). This diboson production is frequently measured, but typically only in leptonic decays at hadron colliders, as there is less background in these channels. This analysis attempts to provide a useful confirmation on these experiments by analyzing the diboson production in an independent decay channel. As the event signature is also produced by strong force interactions, this electroweak signal composes a relatively small fraction of the events observed at CDF. In order to distinguish between the two, an artificial neural network was trained to separate the signal events from the primary background. While the result was measured to be consistent with the Standard Model prediction, large statistical and significant systematic errors limit the utility of this measurement.</p>

The phase transition at the QCD critical end point is believed to be in the 3D Ising universality class. A recently proposed method of using low order Taylor series coefficients to pinpoint the location of the QCD critical end point is tested with the Ising Model. The finding is that one cannot rely solely on the lowest order series coefficients to accurately locate the Ising critical point, and moreover, the values of higher order coefficients are clouded with statistical uncertainty. The method does manage to qualitatively capture the features of the Ising Model phase diagram. / La transition de phase au point critique de la chromodynamique quantique est censé d'appartenir à la classe d'universalité d'Ising à 3D. Une méthode récemment proposée qui emploie la série de Taylor de certaines fonctions thermodynamiques pour déduire l'emplacement de ce point critique est testée avec le modèle d'Ising. La conclusion est qu'on ne peut pas compter uniquement sur les coefficients d'ordre bas de cette série pour localiser avec précision le point critique. D'ailleurs, les coefficients d'ordre supérieur sont difficiles à calculer à cause de l'incertitude statistique. Néanmoins, on trouve que la méthode décrit avec succès les caractèristiques qualitatives du diagramme des phases du modèle d'Ising. fr

A precision measurement of the jet energy scale is essential for the success of the ATLAS experiment. This thesis investigates the suitability of pt balancing in Z + Jet events as an in situ technique for assessing the performance of the jet energy calibration. While the technique is shown to have a kinematic bias in the region Z pt less than 60 GeV/c, it is useful for studying jet performance at higher Z pt. The effects of background processes and signal selection criteria on the pt balance are studied. This study also investigates the performance of jet reconstruction with various jet input constituents, jet algorithms and sizes, and jet calibration schemes. / Une mesure precise de l'echelle d'energie des jets est indispensable pour la reussite de l'experience ATLAS. La presente these examine la viabilite de l'equilibrage en pt dans les evenements Z + Jet en tant que technique in situ pour l'estimation de la performance de la calibration des jets. Bien que cette technique s'avere biaisee dans la region cinematique Z pt moins que 60 GeV/c, il est demontre qu'elle est utile dans un regime a haut pt. Les effets des differentes contributions au bruit de fond ainsi que les criteres de selection du signal sur l'equilibrage en pt sont etudies. Cette etude examine aussi la performance de la reconstruction des jets avec differents constituants de jets, algorithmes et methodes de calibration.

The production of neutral meson resonances in deep inelastic scattering has been studied in DESY with the ZEUS detector at the HERA collider. The rho 0, f0(980) and f2(1270) total cross sections, as well as differential pT and eta cross sections, were measured in the 0 GeV &lt; pT &lt; 7 GeV and |eta| &lt; 1 ranges. The obtained total cross sections were sr0 = 19.21 +/- 0.92 (stat.) +/- 7.59 (syst.) nb, sf0 = 0.63 +/- 0.04 (stat.) +/- 0.25 (syst.) nb and sf2 = 3.62 +/- 0.02 (stat.) +/- 1.73 (syst.) nb. The cross sections measurements for f0 and f2 mesons are underestimated since acceptances had to be overestimated. The measurements were performed on a data sample with 82.5 nb-1 of integrated luminosity and for a squared momentum transfer greater than 3 GeV2 .

The DO experiment at Fermilab records the results of high energy collisions between protons and antiprotons. These high energy particle collisions often result in the production of collimated jets of secondary particles. The trigger system selects, in real time, collision events to be analysed via a detailed reconstruction. A fast reconstruction and identification of particle jets and other physics objects is done in the trigger system in the event selection process. Two possible improvements to the jet reconstruction software algorithm for the trigger system were implemented. The improvement that emulates the offline reconstruction software was found to yield a jet trigger rate reduction of up to 14% without reducing the trigger system performance. As such, it is favored for use in the online trigger system. The performance of the trigger system at reconstructing jets is measured from data. Biases of the measurement methods are identified and quantified. Measured efficiencies are then used to emulate the online trigger response in simulated events.

Cosmic strings are linear concentrations of trapped energy produced throughsymmetry breaking processes of eld theory models. Though they can onlycontribute a maxiumum of 10 percent to structure formation they have beenshown to arise as a generic consequence of many inationary setups of supergravitymodels. In addition they provide another avenue to probe physicsbeyond the "Standard Model". Cosmic strings can intersect producing stringloops. These topological defects are formed at early times creating largeamounts of accretion and thus lead to large amounts of baryon overdensities.These baryonic overdensities of hydrogen lead to a unique 21cm signature.We focus on cosmic string loops in addition to global monopoles and computethe 21cm signature produced by these structures. It is found that both defectsproduce an elliptical region in 21cm radiation maps with a large emissionsignal which may serve as a prediction for upcoming 21cm redshift surveys. / Les défauts topologiques sont des configurations linéaires d'énergie concentrée produites par certaines brisures de symétries en théorie des champs. Aussi fût-il montré qu'ils sont une conséquence de plusieurs modèles de supergravité. Ces défauts topologiques, formés très tôt dans l'évolution de l'univers, créent d'importantes quantités d'accrétion et produisent une grande quantité de surdensité de baryons. Les surdensités de baryons d'hydrogène génèrent une signature unique de 21cm. Nous focussons sur deux défauts topologique particuliers soit le monopole global et la corde cosmique bouclée et calculons la signature à 21cm produite par chacunes de ces structures. Nous montrons que les deux défauts topologique ci-haut produisent une région elliptique dans la carte de radiation à 21cm avec un grand signal d'émission qui pourrait éventuellement servir comme prédiction pour le future relevé du décalage vers le rouge à 21cm.

This thesis presents the searches for two rare B meson decays: the radiative leptonic decay B+ -> l+ nu gamma (l = e, mu) and the flavor-changing neutral current B -> K(*) nu nubar. These searches use the full dataset collected by the BaBar experiment, which corresponds to almost 500 million BB pairs. After fully reconstructing the hadronic decay of one of the B mesons in Upsilon(4S) -> BB decays, evidence of B+ -> l+ nu gamma or B -> K(*) nu nubar is looked for in the rest of the event. No significant evidence of either signal decay is observed. Model-independent branching-fraction upper limits are set at BR(B ->e nu gamma)<17 x10^{-6}, BR(B ->mu nu gamma)<24 x10^{-6}, and BR(B ->l nu gamma)<15.6 x10^{-6}, all at the 90% confidence level. These are currently the most stringent published upper limits for B+ -> l+ nu gamma. In addition, branching-fraction upper limits are set at BR(B -> K+ nu nubar)<3.7 x10^{-5}, BR(B -> K0 nu nubar)<8.0 x10^{-5}, BR(B -> K*+ nu nubar)<11.5 x10^{-5}, and BR(B -> K*0 nu nubar)<9.2 x10^{-5}, all at the 90% confidence level. For additional sensitivity to New Physics contributions, partial B -> K(*) nu nubar branching-fraction upper limits are also determined over the full kinematic range. / Cette thèse présente l'étude de deux désintégrations rares de mésons B: la désintégration radiative leptonique B+ -> l+ nu gamma (l = e, mu) et le courant neutre qui change la saveur B -> K(*) nu nubar. Ces études utilisent l'ensemble des données recueuillies par l'expérience BaBar, ce qui correspond à près de 500 millions paires BB. Après la reconstruction totale de la désintégration hadronique de l'un des mésons B dans la désintégration Upsilon(4S) -> BB, la manifestation de B+ -> l+ nu gamma ou B -> K(*) nu nubar est recherché dans le reste de l'événement. Aucune preuve significative de la désintégration du signal n'a été observée. Les limites supérieures du rapport d'embranchement indépendantes du modèle sont évaluées à BR(B -> e nu gamma)<17 x10^{-6}, BR(B -> mu nu gamma)<24 x10^{-6}, et BR(B -> l nu gamma)<15,6 x10^{-6}, à un niveau de confiance de 90%. Ce sont actuellement les limites supérieures les plus strictes publiés pour B+ -> l+ nu gamma. De plus, les limites supérieure du rapport d'embranchement sont évaluées à BR(B -> K+ nu nubar)<3,7 x10^{-5}, BR(B -> K0 nu nubar)<8,0 x10^{-5}, BR(B -> K*+ nu nubar)<11,5 x10^{-5}, et BR(B -> K*0 nu nubar)<9,2 x10^{-5}, à un niveau de confiance de 90%. Pour demeurer réceptives aux contributions de la nouvelle physique, les limites supérieures du rapport d'embranchement partiel de B -> K(*) nu nubar sont déterminés dans le spectre cinématique complet.

This thesis discusses the measurement of the dE/ dx resolution of the BaBar drift chamber. The study was performed on the data obtained with a small scale prototype drift chamber (built at LAPP, Annecy, France) during test beam runs at CERN (PS) and Zurich (PSI). Drift chamber simulations were performed in order to study the expected performance. Good tracking, necessary in the analysis of the PS runs but unnecessary in the PSI runs, was obtained by performing a chi2 minimization of the space residuals, yielding a time to distance function. An average tracking resolution of &ap;350mum was achieved. The resolution result for seven energy loss samplings per event was scaled up to 40 samples per event which will be available in the BaBar chamber. The expected dE/ dx resolution of the BaBar chamber, as obtained from the PS runs, is: (7.3 +/- 0.1 +/- 0.5)%. The result from the PSI runs is: (6.9 +/- 0.4 +/- 0.5)%.

We study the parametric excitation of entropy perturbations during the reheating stage of Roulette Inflation. Parametric resonance of these entropy modes may induce a large contribution to the large scale curvature fluctuations. After a brief overview of the theory of cosmological perturbations and reheating, we introduce the model of Roulette inflation and go on to showing that preheating of the metric fluctuations does happen, thus imposing constraints on the model. The work requires the analysis of the stability behaviour of a modified form of the Mathieu equation. It is found that this new type of equation is in general more unstable than the Mathieu equation. / Nous étudions l'excitation paramétrique des perturbations de l'entropie durant la période dite de réchauffement dans le contexte du modèle d'inflation Roulette. La résonance paramétrique de ces modes d'entropie peut induire des perturbations dans la courbure adiabatique de l'espace-temps a grande échelle. Après un courte mise en introduction de la théorie des perturbations cosmologiques et du mécanisme dit de réchauffement, nous présentons le modèle d'inflation Roulette et démontrons que l'accroissement paramétrique des perturbations de la métrique a bel et bien lieu, ce qui nous permet de restreindre le domaine d'applicabilité du modèle Roulette. Ce résultat repose sur l'analyse de stabilité d'une version modifiée de l'équation de Mathieu. Il est demontré que cette version modifiée est en fait plus instable que l'équation de Mathieu.