In this dissertation we study supersymmetric particles in four spacetime dimensions and their relations to other physical observables. For a large class of four-dimensional N=2 systems, the supersymmetric particles are described by the ground states of certain quiver quantum mechanics in the low energy limit. We derive a localization formula for the index of quiver quantum mechanics with four supercharges. Our answer takes the form of a residue integral on the complexified Cartan subalgebra of the gauge group. The wall-crossing phenomenon appears as discontinuities in the value of the residue integral as the integration contour is varied. We then move on to study the ground states in the Kronecker model of quiver quantum mechanics. This is the simplest quiver with two gauge groups and bifundamental matter fields, and appears universally in four-dimensional N=2 systems. The ground state degeneracy may be written as a multi-dimensional contour integral, and the enumeration of poles can be simply phrased as counting bipartite trees. We solve this combinatorics problem, thereby obtaining exact formulas for the degeneracies of an infinite class of models. For large ranks, the ground state degeneracy is exponential with the slope being a modular function that we are able to compute at integral values of its argument. We also observe that the exponential of the slope is an algebraic number and determine its associated algebraic equation explicitly in several examples. The speed of growth of the degeneracies, together with various physical features of the bound states, suggests a dual string interpretation. In the last part of the dissertation, we conjecture a precise relationship between a limit of the superconformal index of four-dimensional N=2 field theories, which counts local operators, and the spectrum of BPS particles on the Coulomb branch. We verify this conjecture for the case of free field theories, N=2 QED, and SU(2) gauge theories coupled to matter. Assuming the validity of our proposal, we compute the superconformal index of all Argyres-Douglas theories. Our answers match expectations from the connection of Schur operators with two-dimensional chiral algebras. / Physics

Astronomical observation suggests the existence of near-extreme Kerr black holes in the sky. Properties of diffeomorphisms imply that dynamics of the near-horizon region of near-extreme Kerr are governed by an infinite-dimensional conformal symmetry. This symmetry may be exploited to analytically, rather than numerically, compute a variety of potentially observable processes. In this thesis we compute the gravitational radiation emitted by a small compact object that orbits in the near-horizon region and plunges into the horizon of a large rapidly rotating black hole. We study the holographically dual processes in the context of the Kerr/CFT correspondence and find our conformal field theory (CFT) computations in perfect agreement with the gravity results. We compute the radiation emitted by a particle on the innermost stable circular orbit (ISCO) of a rapidly spinning black hole. We confirm previous estimates of the overall scaling of the power radiated, but show that there are also small oscillations all the way to extremality. Furthermore, we reveal an intricate mode-by-mode structure in the flux to infinity, with only certain modes having the dominant scaling. The scaling of each mode is controlled by its conformal weight. Massive objects in adiabatic quasi-circular inspiral towards a near-extreme Kerr black hole quickly plunge into the horizon after passing the ISCO. The post-ISCO plunge trajectory is shown to be related by a conformal map to a circular orbit. Conformal symmetry of the near-horizon region is then used to compute analytically the gravitational radiation produced during the plunge phase. Most extreme-mass-ratio-inspirals of small compact objects into supermassive black holes end with a fast plunge from an eccentric last stable orbit. We use conformal transformations to analytically solve for the radiation emitted from various fast plunges into extreme and near-extreme Kerr black holes. / Physics

This dissertation describes a model-agnostic search for new resonant phenomena decaying to two jets (dijets) in 3.6 fb-1 of proton-proton collisions at center-of-mass energy sqrt(s)=13 TeV. The collisions were produced by the Large Hadron Collider and recorded by the ATLAS detector in 2015. A dijet invariant mass spectrum is examined for local excesses above a data-driven background estimation accounting for Standard Model production. No statistically significant excess is observed. New physics models are excluded at 95% credibility-level for quantum black holes with production mass thresholds below 5.3 TeV, 8.1 TeV, and 8.3 TeV for three different production scenarios and for excited quarks of masses less than 5.2 TeV. Furthermore, limits are provided on generic Gaussian signal shapes for additional generalization of the 2015 dijet resonant analysis search results. / Physics

This dissertation presents the observation and measurement of the Higgs boson in the H→ WW*→ ℓνℓν channel at √s = 7 TeV and √s = 8 TeV and a search for Higgs pair production in the HH→ bb̄bb̄ channel at √s = 13 TeV with the ATLAS detector in pp collisions at the Large Hadron Collider. First, the discovery of a particle consistent with the Higgs boson in 4.8 fb−1 at √s = 7 TeV and 5.8 fb−1 at √s = 8 TeV is discussed. Then, the measurement of the Higgs boson signal strength and cross section in both the gluon fusion and vector boson fusion (VBF) production modes using 20.3 fb−1 of √s = 8 TeV data combined with 4.8 fb−1 of 7 TeV data is shown. The combined signal strength is measured to be µ = 1.09−0.21+0.23. The total observed significance of the H → WW∗ process is observed to be 6.1σ (with 5.8 σ expected). Advanced methods for background reduction and estimation, particularly in same-flavor lepton final states, are shown. The VBF signal strength is measured to be µVBF = 1.27−0.45+0.53 with an observed significance of 3.2σ (with 2.7 σ expected). In the VBF channel, a selection requirement based method, the precursor to the final multivariate technique used for the result, is detailed. Finally, a search for Higgs pair production in the bb̄bb̄ final state with 3.2 fb−1 at √s = 13 TeV is presented. A particular focus is placed on a tailored signal region for resonant production of Higgs pairs at high masses. No significant excesses are observed, and upper limits on cross sections are placed for spin-2 Randall Sundrum gravitons (RSG) and narrow spin zero resonances. The cross section of σ(pp → GKK* → hh → bbbb) with k/MPl=1 is constrained to be less than 70 fb for masses in the range 600 < mGKK* < 3000 GeV. The cross section upper limits for σ(pp → H → hh → bbbb) range from 30 to 300 fb in the mass range of 500 < mH < 3000 GeV. / Physics

L'étude présentée ici vise à déterminer la relation fonctionnelle existant entre la densité de grains de la trace d'une particule chargée dans l'émulsion nucléaire et le rapport p/mc de cette particule, ou p est la quantité de mouvement, m la masse et c la vitesse de la lumière. L'étude est menée a l'aide des émulsions, de type FUJI ET-7B, exposé dans le cadre de l'expérience E-531 (FNAL), ou se trouvaient réunies des émulsions nucléaires et des détecteurs électroniques, les densités de grains provenant des premières et les quantités de mouvement et les masses des seconds. La relation fonctionnelle observée peut être théoriquement expliquée en termes de deux effets électrodynamiques : la perte d'énergie par ionisation et le rayonnement de transition. Un accord quantitativement satisfaisant ne peut toutefois être obtenu qu'en introduisant dans la modélisation une fonction de résolution pour l'émulsion nucléaire, permettant de tenir compte des caractéristiques du processus photographique. Les modèles de perte d'énergie de Sternheimer (la perte d'énergie restreinte et la perte d'énergie la plus probable), qui ne permettent pas d'inclure une telle fonction, s'avèrent en désaccord, au plan quantitatif, avec les résultats expérimentaux. Un modelé, adapte des travaux de Fano et d'Allison, Bunch et Cobb en particulier, s'accorde avec les résultats expérimentaux si l'on ne tient compte, par le biais de la fonction de résolution, que des transferts d'énergie supérieurs à 90 eV et inférieurs à 1,4 keV. Dans le cas du rayonnement de transition, une fonction de résolution différente est requise, ou ne sont retenus que les transferts d'énergie s'étendant d'environ 450 eV jusqu'à 1,4 keV. La différence dans la fonction de résolution pour les deux effets électrodynamiques peut légitimement être expliquée par le fait qu'il s'agit de deux rayonnements actiniques différents.

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No description available.

Cette these decrit le travail effectue dans l'emulsion nucleaire pour l'experience E-531 qui avait pour but de mesurer les temps de vie des particules charmees. Les plaques d'emulsion ont ete exposees au faisceau de neutrinos produit par l'interaction de protons de 400 GeV avec une cible de BeO au Fermi National Accelerator Laboratory. Les evenements neutrinos trouves ont ete analyses et les candidats charmes identifies. Un evenement en particulier a ete etudie en profondeur. Il s'agit de la desintegration par interaction faible d'une particule neutre qui n'a pu etre reconstruite en un $D\sp0$. Apres l'essai de plusieurs hypotheses, l'interpretation la plus probable pour l'evenement est celle qui implique la production et la desintegration d'une particule contenant un quark beaute et probablement aussi un quark etrange (le meson $B\sbsp{s}{0}$). Le temps de vie de cette particule d'une etrange beaute serait d'environ 10$\sp{-12}s$. Les distributions de pseudorapidites provenant des evenements neutrino sont analysees a l'aide de moments factoriels. Ces moments manifestent une variation en loi de puissance en fonction de la resolution de la pseudorapidite. Ce comportement est appele intermittence et peut etre caracterise par l'exposant d'echelle $\nu$ qui possede des qualites universelles. La valeur obtenue pour les interactions neutrino-emulsion, $\nu$ = 1.84 $\pm$ 0.14, est plus elevee que pour toute autre interaction. Ceci est le reflet d'un processus dynamique autosimilaire base sur des mecanismes de cascade. L'etude multifractale, effectuee a l'aide des dimensions generalisees et des moments $G\sb{q}$ de Hwa, corrobore cette observation.

<p> An interpretation of CMS searches for evidence of supersymmetry in the context of the minimal supersymmetric Standard Model (MSSM) is given. It is found that supersymmetric particles with color charge are excluded in the mass range below about 400 GeV, but neutral and weakly-charged sparticles remain non-excluded in all mass ranges. Discussion of the non-excluded regions of the model parameter space is given, including details on the strengths and weaknesses of existing searches, and recommendations for future analysis strategies. Advancements in the modeling of events arising from quantum chromodynamics and electroweak boson production, which are major backgrounds in searches for new physics at the LHC, are also presented. These methods have been implemented as components of CMS searches for supersymmetry in proton-proton collisions resulting in purely hadronic events (i.e., events with no identified leptons) at a center of momentum energy of 13 TeV. These searches, interpreted in the context of simplified models, exclude supersymmetric gluons (gluinos) up to masses of 1400 to 1600 GeV, depending on the model considered, and exclude scalar top quarks with masses up to about 800 GeV, assuming a massless lightest supersymmetric particle. A search for non-excluded supersymmetry models is also presented, which uses multivariate discriminants to isolate potential signal candidate events. The search achieves sensitivity to new physics models in background-dominated kinematic regions not typically considered by analyses, and rules out supersymmetry models that survived 7 and 8 TeV searches performed by CMS.</p>

The main objective of this thesis is to study and investigate the production of massive vector bosons (W+ and W−). This a priori mentioned production is not sensitive to hot nuclear matter effects because of the weak coupling nature of these vector bosons. Thus, in heavy ion collisions they provide a good reference for the medium-induced effects on other probes. The production mechanism of these vector bosons is highly isospin dependent and thus they are affected by the initial state effects. Initial state effects include isospin, Fermi motion, EMC effect, shadowing and nuclear absorption. Hence their production in lead-lead (Pb-Pb) and proton-lead (p-Pb) collisions can be used to test some of these initial state effects. In this thesis only two of these initial state effects will be considered namely, isospin and shadowing (referring to shadowing and anti-shadowing). Eke, these vector bosons can be used to provide a non-arbitrary reference to the probes affected by the medium. Traditionally, in heavy ion collisions, hard processes are expected to scale with the number of binary collision thus a precise study of these vector bosons can be used to test the factorisation assumed in models used to determine centrality. This unique property of electroweak (W) bosons makes them essential probes to study the possible inherent bias in centrality determination. In proton-proton (pp) collisions, their production can be used to obtain information on quark parton distribution functions (PDF). The data used in the analysis was collected by A Large Ion Collider Experiment (ALICE) at the Large Hadron Collider (LHC). The ALICE detector is designed to study ultrarelativistic heavy-ion collisions, in which a hot and dense, strongly-interacting medium is created. The production of W bosons is studied in p-Pb, p-p and Pb-Pb collisions at 5.023, 8 and 5.023 TeV centre-of-mass energies, respectively. The forward muon spectrometer with the pseudorapidity acceptance −4.0 < ŋ < −2.5 is used. W bosons are studied via the inclusive single muon differential pT spectrum.