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DisciplineGraduate College (401)

Physics (401)

AuthorsVisscher, Koen (29)Su, Shufang (24)Shupe, Michael (22)Melia, Fulvio (15)Bowen, Theodore (14)Hill, Henry A. (14)Mazumdar, Sumit (14)Mazumdar, Sumitendra (14)Manne, Srinivas (13)Stafford, Charles (13)View MoreTypestext (401)Dissertation-Reproduction (electronic) (284)Electronic Dissertation (117)
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Thermalization theory in heavy ion collisions by nonequilibrium statistical mechanics.

Abu-Samreh, Mohammad Mahmud. (The University of Arizona., 1991)

This dissertation presents a semiclassical microscopic approach based on the Uehling-Uhlenbeck equation for studying the equilibration processes due to nucleon-nucleon collisions during the collision of two heavy ions in the low and intermediate energy domain (5-100 MeV/nucleon). The state formed in the early stages of a heavy-ion collision can be characterized by a highly excited non-equilibrium system of nucleons. Equilibration processes then take place resulting in a system for which a temperature can be defined at least locally. The single-nucleon distribution function for the nucleons during the early stage of the ion-ion collision is represented in momentum-space either by two Fermi-spheres separated by the relative momentum of the impacting ions or by a deformed Fermi-sphere. The equilibration (thermalization) of this initial distribution in momentum-space is studied by calculating the collision term as a function of time. The relaxation-times are investigated through a microscopic model that incorporates the UU collision term with the relaxation-time approximation. Relaxation-times for the equilibration are obtained as a function of density and temperature. The temperature dependence is strong at low temperatures and this is a consequence of the Fermi statistics. The mode dependence of the relaxation-times is also calculated by expanding the angular dependence of the distribution in spherical harmonics. The RTA is also tested against thermalization of the Fermi-sphere systems and is found to be reasonable. Transport coefficients for viscosity, thermal conductivity and diffusion are also calculated as well as their temperature and density dependencies. Their relation to relaxation-times are derived. The mean free path of nucleons in hot nuclear matter is also studied in the same frame of work. The numerical calculations of the collision term are an important part of this investigation. They involve five-dimensional integrations carried out using Gaussian and Simpson's numerical methods.

Testing General Relativity in the Strong-Field Regime with Observations of Black Holes in the Electromagnetic Spectrum

Johannsen, Tim (The University of Arizona., 2012)

General relativity has been tested by many experiments, which, however, almost exclusively probe weak spacetime curvatures. In this thesis, I create two frameworks for testing general relativity in the strong-field regime with observations of black holes in the electromagnetic spectrum using current or near-future instruments. In the first part, I design tests of the no-hair theorem, which uniquely characterizes the nature of black holes in terms of their masses and spins in general relativity and which states that these compact objects are described by the Kerr metric. I investigate a quasi-Kerr metric and construct a Kerr-like spacetime, both of which contain an independent parameter in addition to mass and spin. If the no-hair theorem is correct, then any deviation from the Kerr metric has to be zero. I show that already moderate changes of the deviation parameters in either metric lead to significant modifications of the observed signals. First, I apply this framework to the imaging of supermassive black holes using very-long baseline interferometry. I show that the shadow of a black hole as well as the shape of a bright and narrow ring surrounding the shadow depend uniquely on its mass, spin, inclination, and the deviation parameter. I argue that the no-hair theorem can be tested with observations of the supermassive black hole Sgr A*. Second, I investigate the potential of quasi-periodic variability observed in both galactic black holes and active galactic nuclei to test the no-hair theorem in two different scenarios. Third, I show that the profiles of relativistically broadened iron lines emitted from the accretion disks of black holes imprint the signatures of deviations from the Kerr metric. In the second part, I devise a method to test the predicted evaporation of black holes in the Randall-Sundrum model of string theory-inspired braneworld gravity through the orbital evolution of black-hole X-ray binaries and obtain constraints on the size of the extra dimension from A0620-00 and XTE J1118+480. I predict the first detection of orbital evolution in a black-hole binary.

Numerical solutions of lattice quantum fields with a hierarchy of Schroedinger-like equations.

Ludwig, Mark Allen. (The University of Arizona., 1990)

Systems of quantized fields can be described by an infinite hierarchy of coupled equations. Such a hierarchy is derived from first principles for a simple interacting field theory to illustrate this type of a representation. The perturbation series for the S matrix is derived from the hierarchy equations in order to show its equivalence to the usual expansion in Feynman amplitudes. An inquiry is then conducted to determine whether this type of representation is useful for solving problems. Truncations of the hierarchy which predict simple bound states are examined in the weak coupling limit, and equations describing a hydrogen-like atom are obtained. Next, the numerical approximation of a truncated hierarchy is studied, and a scattering/particle creation process is modeled in one dimension with a resulting accuracy of 1 to 2 percent. Finally, the mathematical questions of convergence which arise in connection with quantized fields are discussed within the context of the hierarchy equations.

Dynamics of a coherently driven micromaser.

Slosser, John Jason. (The University of Arizona., 1990)

This dissertation considers both a lossless and a dissipative micromaser in which a monoenergetic beam of two-level atoms in a coherent superposition of their upper and lower states is injected inside a single mode, high-Q cavity. In the lossless case, we find that under appropriate conditions a field initially in a mixed state will evolve to previously unknown pure states, which we call the tangent and cotangent states. In various limits, these states exhibit interesting properties such as sub-Poissonian photon statistics and squeezing, and most importantly they acquire the characteristics of "macroscopic" quantum superpositions. When dissipation of the cavity mode is incorporated into the model, we find that although the field no longer evolves to a pure state, the mixed steady-state field may still retain the properties of a macroscopic superposition under experimentally realizable damping rates. We then evaluate the experimental conditions necessary for the preparation and detection of such macroscopic superpositions.

Measurement of the bottom quark anti bottom quark cross section and correlations using dimuon events in proton antiproton collisions at 1.8 TeV.

Fein, David Kevin. (The University of Arizona., 1996)

We have measured the b-quark production cross section for |y| < 1 using a sample of dimuon events collected with the DO detector in proton antiproton collisions at √s = 1.8 Te V at the Fermilab Tevatron. The measured b-quark cross section is consistent with O(ɑ³(s)) QCD predictions, but lies at the upper limit of the theoretical uncertainties which is a factor of 1.5 above the mean value. A study of the difference in azimuthal angle of the two muons is in good qualitative agreement with the O(ɑ³(s)) QCD predictions.

Attosecond Resolved Electron Wave Packet Dynamics in Helium

Hirisave Shivaram, Niranjan (The University of Arizona., 2013)

Electron dynamics in atoms and molecules occurs on a time-scale of attoseconds (10⁻¹⁸s). With the availability of strong field (∼ 10¹²- 10¹³ W cm⁻²) femtosecond (10⁻¹⁵s) laser pulses with electric fields that can reach and exceed the Coulomb field strength experienced by an electron in the ground state of an atom, it is now possible to generate even shorter pulses with durations on the order of attoseconds by the process of high-harmonic generation (HHG). In this dissertation, experiments to study electron dynamics on attosecond time-scales in a helium atom using attosecond pulses generated by HHG will be described. We use extreme-ultraviolet (XUV) attosecond pulse trains and strong femtosecond near-infrared (IR) laser pulses to excite and ionize helium atoms. We first discuss an experimental technique that allows us to quantify and reduce the detrimental effects of Gouy phase slip on attosecond XUV-IR experiments. We then discuss our experiments to study the dynamic behavior of electronic states in a strong field modified helium atom where we use attosecond pulses to explore the strong-field modified atomic landscape. Using the Floquet theory to interpret our experimental observations we measure the variation in quantum phase of interferences between different fourier components of Floquet states as the IR intensity is varied and as different ionization channels dominate, in real-time. Next, we briefly discuss quantum interferences between photo-electrons ionized from XUV excited states in helium using an IR field which is polarized orthogonal to the XUV polarization. We observe variation in angular distribution of photo-electrons as a function of XUV-IR time-delay. We then discuss a new technique to measure the time-of-birth of attosecond pulses using XUV+IR photo-ionization in helium as a measurement probe. Finally, experiments to study the evolution of XUV excited wave-packets in helium on a time-scale of 100's of femtoseconds with attosecond resolution will be described.

Scanning Probe Microscopy of Graphene and Carbon Nanotubes

Xue, Jiamin (The University of Arizona., 2012)

This dissertation presents research on scanning probe microscopy and spectroscopy of graphene and carbon nanotubes. In total three experiments will be discussed. The first experiment uses a scanning tunneling microscope (STM) to study the topographic and spectroscopic properties of graphene on hexagonal boron nitride (hBN). Graphene was first isolated and identified on SiO₂ substrates, which was later found to be the source of graphene quality degradation, e.g. large surface roughness, increased resistivity and random doping etc. Researchers have been trying to replace SiO₂ with other materials and hBN is by far the most successful one. Our STM study shows an order of magnitude reduction in surface roughness and electrostatic potential variation compared with graphene on SiO₂.The second experiment shows a novel quantum interference effect of electron waves in graphene, loosely referred to as "Friedel oscillations." These arise when incident electron waves interfere with waves scattered from defects in the sample. This interference pattern shows up as a spatial variation in the local density of states, which can be probed by the STM. We measured such Friedel oscillations in graphene near step edges of hBN. Due to its peculiar band structure, the oscillations in graphene have a faster decay rate and their wavelength is an order of magnitude longer than similar oscillations previously observed on noble metal surfaces. By measuring the dependence of the Friedel oscillations on electron energy, we map out the band structure of graphene. The last experiment studies a different system: carbon nanotube quantum dots. By combining scanning probe microscopy and transport measurements, we obtain spatial information about quantum dots formed in a carbon nanotube field effect transistor. We also demonstrate the ability to tune the coupling strength between two quantum dots in series.

Elastic properties of polymeric Langmuir-Blodgett films studied using Brillouin light scattering.

Lee, Sukmock. (The University of Arizona., 1991)

Brillouin light scattering (BLS) experiments have been performed on polymeric uniaxial Langmuir-Blogett (LB) films, whose preferred axes are in the plane of the film, to investigate their elastic properties. By assigning the spectral signals unambiguously, the whole set of the elastic constants and the indices of refraction were determined. As the monolayer thickness increased from 16.5 to 20.5 A, the elastic constants decreased and the refractive indices were not changed. These decreasing elastic constants were interpreted in terms of a superlattice model of the polymeric LB films. BLS coupled with surface-plasmon-polaritons was studied to not only enhance the Brillouin signal by more than a factor of 15, but also to study the hybridization of the dispersion relations between the guided modes of a CdA LB film and the Rayleigh-Sezawa modes of the supported Ag film coated on a prism. The Kretschmann ATR geometry was used. The angular dependence of the intensity of the surface-plasmon-polariton-enhanced BLS for a prism-metal-dielectic system was also studied.

Nuclear and molecular processes in muon-catalyzed fusion.

Harley, David. (The University of Arizona., 1991)

The dt-αn continuum in the presence of the muon is studied in detail, and it is shown that the existence of extended continuum states just beneath the d+(tμ)₁(s) threshold can lead to a variety of 'pseudoresonant' fusion processes with a temperature and density dependence distinct from those leading to molecular formation. Various in-flight and pseudoresonant fusion reaction cross sections involving the excitation of electromolecular states and two or three scattering bodies are computed. Fusion processes in very dense plasmas of ∼10³ liquid hydrogen density are studied, and it is shown that in this environment both sticking and muon transfer problems are eliminated, and that pseudoresonant fusion processes should dominate. In this context, the use of negatively charged hadrons as potential catalytic particles is also considered.

Intermittency, moments and correlations in distributions of particles created in high-energy collisions.

Eggers, Hans Christoph. (The University of Arizona., 1991)

Intermittency, as introduced into multiparticle production by Bialas and Peschanski, has become a fruitful and rapidly growing industry. The original concept of intermittency in the form of the Alpha model is discussed in detail and suggestions for extensions are made. We analyze the factorial moments measured by different experimental collaborations in terms of their nontrivial many-particle correlations, the cumulants. A large fraction of measured moments is shown to originate in two-particle correlations. The validity of the Linked Pair ansatz is tested and found to be acceptable to fourth order for hadronic collisions but uncertain for nuclear collisions. A cumulant decomposition for bin-bin correlations is derived, and a general formalism is developed for treating correlations of particle distributions consisting of several distinct populations, such as particles of different charge.

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