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Thesis--University of California, Berkeley, 1961. / "UC-4 Physics" -t.p. "TID-4500 (16th Ed.)" -t.p. Includes bibliographical references (p. 88-91).

Jet production in PbPb collisions at a per-nucleon center-of-mass energy of 2.76 TeV has been studied using the ATLAS detector at the LHC. Interactions between the high- pT partons and the hot, dense medium, produced in these ultrarelativistic collisions, are expected to cause the loss of the jet energy (jet quenching). This thesis presents results of the jet analysis done on the data taken during the 2011 heavy-ion run at the LHC as well as PYTHIA Monte Carlo reference. Jets are reconstructed using the anti-kt jet clustering algorithm and studied as a function of collision centrality and dijet energy imbalance. With increasing centrality, dijets are observed to be increasingly asymmetric, consistent with the theory of jet quenching. The study of charged particle tracks indicates the increase of the low-pT tracks in the strongly quenched jets. 1

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The Quark-Gluon Plasma (QGP) produced in heavy-ion collisions has been shown to behave like a nearly perfect fluid, characterized by a very low ratio of shear viscosity to entropy density. Significant measurements in large collision systems have improved the constraints on the value of 𝜂/𝑠. However, the precise temperature dependence of 𝜂/𝑠 still remains unknown. The interplay between viscous effects and initial geometry fluctuations is important that requires further investigation. Another key open question in the study of multi-particle production is the relationship between the “ridge” – observed azimuthal correlations between particles in the underlying event that extend over all rapidities – and hard or semi-hard scattering processes in small collision systems. In particular, it is not known whether jets or their soft fragments are correlated with particles in the underlying event. This dissertation presents two analyses. The first analysis measures flow harmonics 𝜈2–𝜈6 in 3 𝜇b^-1 of Xe+Xe collisions at √𝑠𝖭𝖭 = 5.44 TeV using the ATLAS detector at the LHC. The centrality, multiplicity, and 𝑝_T dependence of the 𝜈n values obtained using two-particle correlations and template-fit procedure are presented, and the measurements are compared with those in Pb+Pb collisions and 𝑝+Pb collisions at 5.02 TeV. The 𝜈n values in Xe+Xe collisions are observed to be larger than those in Pb+Pb collisions for n = 2, 3, and 4 in the most central events. However, the 𝜈n values in Xe+Xe collisions become smaller than those in Pb+Pb collisions with decreasing centrality or increasing harmonic order n. The 𝜈n in Xe+Xe and Pb+Pb collisions are also compared as a function of the mean number of participating nucleons and the measured charged-particle multiplicity in the detector. The 𝜈3 values in Xe+Xe and Pb+Pb collisions are observed to be similar at the same ⟨𝑁_part⟩ or multiplicity, but the other harmonics are significantly different. The second analysis studies two-particle correlations in pp collisions at 13 TeV using data collected by the ATLAS experiment at the LHC, with an integrated luminosity of 15.8 pb⁻¹, in two different configurations. In the first case, charged particles associated with jets are excluded from the correlation analysis, while in the second case, correlations are measured between particles within jets and charged particles from the underlying event. Second-order flow coefficients, 𝜈2, are presented as a function of event multiplicity and transverse momentum. These measurements show that excluding particles associated with jets does not affect the measured correlations. Moreover, particles associated with jets do not exhibit any significant azimuthal correlations with the underlying event, ruling out hard processes contributing to the ridge.

Metallic bilayer samples of Mo(400 Å)/ Al(substrate) were characterized using Rutherford Backscattering Spectroscopy after first being irradiated with Xe ion beam having an energy of 1.8 MeV. The computer code RUMP was then used to simulate the RBS spectra. The interdiffusion at the interface was considered in terms of thermal spike induced atomic migration. It was found that the coupling of the chemical effect with spike is significant with regard to mixing of the bilayer samples. Furthermore, in addition to the initial contamination of carbon atoms on the surface and at the interface, more carbon atoms were found to be picked up by the surface, this carbon w.as from the vacuum pumps and tended to migrate into the surface once irradiation dose exceeded 11 x 10¹⁵cm². A semi-empirical model was developed for ion beam mixing taking into account collisional mixing and thermal spike effects, as well as the thermal spike shape. The collisional mixing part was accounted for by the Kinchin-Pease model, or, alternatively dynamic Monte Carlo simulation. For the thermal spike, the ion beam mixing parameter Dt/Φ was derived to be proportional to ( - F_D /ΔH_coh)^2+μ, where F_D is the damage energy deposited per unit path length, ΔH_coh is the cohesive energy of the target materials, and µ is a constant dependent on the spike shape and point defect density in the spike regions. The thermal spike introduces a nonlinear effect in the mixing process, distinguishing itself from the linear effect of ballistic mixing. The shape of the thermal spike that best fit the experimental results depends on the magnitude of the cascade density. For relatively high density collisional cascades, where thermal spikes start to be important, it was found that a spherical spike model was more consistent with experimental measurements at low temperatures. However, for extremely high density collisional cascade regions, a cylindrical shaped spike gave better results. The atomic migration energy in the spike regions is scaled by a factor of one out of 8.6 of cohesive energy. The migration mechanism was recognized to be interstitial-dominated one. / M.S.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 1980 / Includes bibliographical references. / by Joel Steven Karp. / Ph. D. / Ph. D. Massachusetts Institute of Technology, Department of Physics

Thesis (MSc (Physics))--University of Stellenbosch, 2009. / Hanbury Brown-Twiss interferometry is a correlation technique by which the size and shape of the emission function of identical particles created during collisions of high-energy leptons, hadrons or nuclei can be determined. Accurate experimental datasets of three-dimensional correlation functions in momentum space now exist; these are sometimes almost Gaussian in form, but may also show strong deviations from Gaussian shapes. We investigate the suitability of expressing these correlation functions in terms of statistical quantities beyond the normal Gaussian description. Beyond means and the covariance matrix, higher-order moments and cumulants describe the form and di erence between the measured correlation function and a Gaussian distribution. The corresponding series expansion is the Gram- Charlier series and in particular the Gram-Charlier Type A expansion found in the literature, which is based on a Gaussian reference distribution. We investigate both the Gram-Charlier Type A series as well as generalised forms based on non-Gaussian reference distributions, as well as the related Edgeworth expansion. For testing purposes, experimental data is initially represented by a suite of one-dimensional analytic non-Gaussian distributions. We conclude that the accuracy of these expansions can be improved dramatically through a better choice of reference distribution, suggested by the sign and size of the kurtosis of the experimental distribution. We further extend our investigation to simulated samples of such test distributions and simplify the theoretical expressions for unbiased estimators (k-statistics) for the case of symmetric distributions.

We perform an event-by-event hydrodynamic analysis for Pb-Pb collisions at the incident energy of sqrt(sNN) = 2.76TeV, also studying the effects of two equations of state under the same initial conditions and freeze-out scenario: one characterized by a critical point and the other based on Lattice QCD (Quantum Chromodynamics) calculations. The observables of interest are particle spectra in terms of pseudorapidity and transverse momentum, as well as flow harmonics, which are coefficients that carry information on the initial anisotropies of the system throughout its evolution. Those are computed and compared with experimental Large Hadron Collider (LHC) data. There are slight differences in the results for each equation of state, caused by their distinct features. Lastly, the LHC-based calculations are compared with previous works related to the Relativistic Heavy-Ion Collider (RHIC) experimental data. The main techniques of the latter are performed in this work, which results in differences between some aspects in the outcome for each collision type, from initial energy distributions to freeze-out temperatures. / É feita uma análise de hidrodinâmica evento-por-evento para colisões de Pb-Pb à energia incidente de sqrt(sNN) = 2.76TeV. Estudamos os efeitos de duas equações de estado sob as mesmas condições iniciais e desacoplamento: uma é caracterizada por um ponto crítico e a outra é baseada em cálculos de Lattice QCD (Cromodinâmica Quântica). Os observáveis de interesse são os espectros de partículas em termos da pseudo rapidez e momento transversal, assim como os coeficientes harmônicos de Fourier que, por sua vez, carregam as anisotropias iniciais do sistema durante toda a sua evolução. Tais observáveis são calculados e comparados com dados experimentais do Large Hadron Collider (LHC). Por fim, os cálculos baseados em parâmetros referentes às energias do LHC são comparados com trabalhos anteriores feitos com base em dados experimentais do Relativistic Heavy-Ion Collider (RHIC). Os principais métodos usados no caso anterior são aplicados a este trabalho, o que resulta em algumas diferenças entre os resultados dos dois tipos de colisão, desde a distribuição de energia inicial a temperaturas de freeze-out.