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- All Subjects: Physics
- Creators: School of Mathematical and Statistical Sciences
- Member of: Barrett, The Honors College Thesis/Creative Project Collection
- Status: Published
efficiencies at high field strengths and prohibits anti-aligned nuclear states from transferring. We also develop a rudimentary theoretical model based on simulated results and partially validate the characteristic transfer times for spin states. This model also establishes a framework for future work including the introduction of a magnetic field.
Despite being bound by the strong force, bottomonium exhibits a rich spectrum of resonances corresponding to excited states extremely analogous to that of positronium or even familiar atomic systems. Transitions between these levels are possible via the absorption or emission of either a photon, gluon, or gluons manifesting as light hadrons. The goal of this thesis was to establish a theoretical value for the currently unmeasured partial decay width for one such transition—the electromagnetic decay channel hb -> etab gamma. To this end, two methods were utilized.
The first approach relied on the presumption of a nonrelativistic constituent quark model interacting via a simple static potential, allowing for radial wave functions and energy eigenvalues to be obtained for the states of interest via the Schrödinger equation. Upon an application of the standard electromagnetic multipole expansion followed by a utilization of the electric dipole E1 decay width formula, a value of 57.7 ± 0.4 keV was obtained.
The second approach stemmed from the effective Lagrangian describing the bottomonium P to S electromagnetic transitions and relied on the presumption that a single coupling constant could be approximated as describing all nP to mS transitions regardless of spin. A value for this coupling constant could then be extracted from the 1P to 1S spin triplet data and used to predict the width for the singlet 1P to 1S transition. The partial decay width value found in this manner was 47.8 ± 2.0 keV.
Various other methods and models have established a predicted range of 35 to 60 keV for this partial decay width. As the values determined in this thesis fall within the expected range, they agree well with our current understanding of this electromagnetic transition and place further confidence on the expected range.
The self-assembly of strongly-coupled nanocrystal superlattices, as a convenient bottom-up synthesis technique featuring a wide parameter space, is at the forefront of next-generation material design. To realize the full potential of such tunable, functional materials, a more complete understanding of the self-assembly process and the artificial crystals it produces is required. In this work, we discuss the results of a hard coherent X-ray scattering experiment at the Linac Coherent Light Source, observing superlattices long after their initial nucleation. The resulting scattering intensity correlation functions have dispersion suggestive of a disordered crystalline structure and indicate the occurrence of rapid, strain-relieving events therein. We also present real space reconstructions of individual superlattices obtained via coherent diffractive imaging. Through this analysis we thus obtain high-resolution structural and dynamical information of self-assembled superlattices in their native liquid environment.
We implemented the well-known Ising model in one dimension as a computer program and simulated its behavior with four algorithms: (i) the seminal Metropolis algorithm; (ii) the microcanonical algorithm described by Creutz in 1983; (iii) a variation on Creutz’s time-reversible algorithm allowing for bonds between spins to change dynamically; and (iv) a combination of the latter two algorithms in a manner reflecting the different timescales on which these two processes occur (“freezing” the bonds in place for part of the simulation). All variations on Creutz’s algorithm were symmetrical in time, and thus reversible. The first three algorithms all favored low-energy states of the spin lattice and generated the Boltzmann energy distribution after reaching thermal equilibrium, as expected, while the last algorithm broke from the Boltzmann distribution while the bonds were “frozen.” The interpretation of this result as a net increase to the system’s total entropy is consistent with the second law of thermodynamics, which leads to the relationship between maximum entropy and the Boltzmann distribution.