Orientador: Donato Giorgio Torrieri / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-30T22:50:16Z (GMT). No. of bitstreams: 1 Gambini_GuillermoGeraldoRivera_M.pdf: 5712404 bytes, checksum: 0da05d8acbfc173eed212a7f6e4f6e27 (MD5) Previous issue date: 2016 / Resumo: A equação de Gribov, Levin e Ryskin (GLR) é uma equação de evolução para as funções de distribuição dos gluons que respeita o limite de Froissart. Motivado pelo fato do fluxo elíptico v2 apresentar scaling no momento transversal, na rapidez, no tamanho do sistema, etc. e pela similaridade que esses scalings possuem com o scaling de Bjorken, modificamos a equação GLR adicionando uma dependência angular a ela. Dessa maneira, temos uma equação diferencial parcial não linear do tipo 2+1 que pode apresentar instabilidades nas soluções, gerando v2. A forma geral das soluções foi inspirada pela descomposição de Fourier para a distribuição de momentos das partículas produzidas em colisões entre íons pesados. Duas soluções para os modos instáveis são obtidas e seus significados físicos discutidos / Abstract: The Gribov-Levin-Ryskin (GLR) equation is an evolution equation for gluon distribution functions which respects Froissart's bound. Motivated by the non-obviousness of elliptic flow v2 scaling in transverse momentum, rapidity, system size, etc. being explained by Hydrodynamics, and the similarity they have with Bjorken scaling, the GLR equation is modified by adding an angular dependence to it; therefore, turning it into a 2+1 nonlinear partial differential equation, which can present instabilities in its solutions, generating v2. The general form of the solutions was inspired by the Fourier decomposition for the momentum distribution of produced particles in heavy-ion collisions. Two solutions for the unstable modes are found and their physical meaning is discussed / Mestrado / Física / Mestre em Física / 1370446/2014 / 151922/2014-4 / CAPES / CNPQ

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Jets are a useful probe of the hot, dense medium produced in heavy ion collisions since partons are expected to lose energy in interactions with the medium through a phenomena called jet quenching. Recent results studying jet quenching in relativistic heavy ion collisions at the LHC with the ATLAS detector are presented here. The jets are reconstructed using the anti-kt algorithm with a background subtraction that removes the large underlying event. A fully unfolded measurement of the dijet asymmetry in Pb+Pb and pp collisions with an integrated luminosity of 0.14 nb^−1 and 4.0 pb^−1, respectively, at √sNN =2.76 TeV is shown. The dijets are found to be highly asymmetric in central Pb+Pb collisions and become more symmetric, or like pp, in more peripheral collisions. A strong p_T dependence to the asymmetry is also observed. This measurement is shown to have similar qualitative features at jet radii of R=0.3 and R=0.4, implying that the underlying event is under control. Measurements of the nuclear modification factor, R_AA, for R=0.4 jets in Pb+Pb and pp collisions with an integrated luminosity of 0.49 nb^−1 and 25 pb^−1, respectively, at √sNN = 5.02 TeV are also presented. The R_AA shows the strongest suppression in central collisions and the least suppression in peripheral collisions. It shows a slight increase with jet p_T and a decrease with increasing rapidity at high p_T. Finally, the dijet asymmetry for R=0.4 jets is also reported in Xe+Xe collisions at √sNN = 5.44 TeV compared to Pb+Pb and pp collisions at √sNN = 5.02 TeV. No difference is observed between Pb+Pb and Xe+Xe collisions, within the uncertainties of the measurement, as a function of the number of participants or the collision centrality.

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ATLAS measurements of the production of muons from heavy flavor decays in √sNN = 2.76 TeV Pb+Pb collisions and √s = 2.76 TeV pp collisions at the LHC are presented. Integrated luminosities of 0.14 nb−1 and 570 nb−1 are used for the Pb+Pb and pp measurements, respectively. The measurements are performed over the transverse momentum range 4 < pT < 14 GeV and for five Pb+Pb centrality intervals. Backgrounds arising from in-flight pion and kaon decays, hadronic showers, and mis-reconstructed muons are statistically re- moved using a template fitting procedure. The heavy flavor muon differential cross-sections and per-event yields are measured in pp and Pb+Pb collisions, respectively. The nuclear modification factor, RAA, obtained from these is observed to be independent of pT, within uncertainties, and to be less than unity, which indicates suppressed production of heavy flavor muons in Pb+Pb collisions. For the 0–10% most central Pb+Pb events, the measured RAA is ∼ 0.35. The azimuthal modulation of the heavy flavor muon yields is also measured and the associated Fourier coefficients vn for n=2, 3 and 4 are given as a function of pT and centrality. They vary slowly with pT and show a systematic variation with centrality that is characteristic of other anisotropy measurements. The measured RAA and vn values are also compared with theoretical calculations. We also present the ATLAS di-muon azimuthal correlation from heavy flavor decay in √√sNN = 5.02 TeV Pb+Pb collisions and s = 5.02 TeV pp collisions. Heavy flavor muons with 4 < pT < 8 GeV are selected. The azimuthal correlations are measured for both same sign muon pairs and opposite sign muon pairs. Comparing with the azimuthal correlations in pp data, Pb+Pb results are observed to have more broadening. Central collisions are also more broadened than peripheral collisions. The integrated luminosities used in the dimuon measurement are 26 pb−1 for the pp data and 0.49 nb−1 for the Pb+Pb data. In ultra-relativistic heavy-ion collisions, dilepton pairs may be produced through the interaction of the large electromagnetic fields of the nuclei. A measurement of γγ → μ+μ− in inclusive Pb+Pb collisions at √sNN = 5.02 TeV using 0.49 nb−1 is presented in this thesis. The contribution from background sources of dimuons is removed using a template fit method. The angular and transverse momentum correlations between the muons are measured as a function of collision centrality. In peripheral collisions, the muons exhibit a strong back-to-back correlation consistent with previous measurements of dimuon production in ultra-peripheral collisions. The correlations are observed to broaden significantly in central collisions. The modifications are qualitatively consistent with attenuation of the muons while passing through the hot matter produced in the collision.

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references. Available also from UMI/Dissertation Abstracts International.