Monte Carlo simulations are performed to study phase transitions of several systems. The 3D Ising model, the 2D 10-state Potts model, the 3D 3-state Potts model, and the SU(2) and SU(3) lattice gauge theories are considered. / For $L\sp{D}$ block geometries, we calculate the density of states and obtain high precision estimates for the leading partition function zeros. The finite-size scaling analysis of the first zero allows the extraction of the critical exponent $\nu$. For first-order phase transitions, the analysis of the specific heat gives an estimation of the latent heat. For $L\sp{D-1}$ $\infty$ cylindrical geometries, we determine the mass-gap m = 1/$\xi$ ($\xi$ is the correlation length). The finite-size scaling analysis of the mass-gap yields another estimate of the critical exponent $\nu$. The often exploited universality between the SU(2) gauge theory and the 3D Ising model critical exponents is confirmed. Our results show also a consistency between the SU(3) and the 3D 3-state Potts model critical exponent $\nu$. / Source: Dissertation Abstracts International, Volume: 52-10, Section: B, page: 5329. / Major Professor: Bernd A. Berg. / Thesis (Ph.D.)--The Florida State University, 1991.

In this dissertation several two dimensional statistical systems exhibiting discrete Z(n) symmetries are studied. For this purpose a newly developed algorithm to compute the partition function of these models exactly is utilized. The zeros of the partition function are examined in order to obtain information about the observable quantities at the critical point. This occurs in the form of critical exponents of the order parameters which characterize phenomena at the critical point. The correlation length exponent is found to agree very well with those computed from strong coupling expansions for the mass gap and with Monte Carlo results. / In Feynman's path integral formalism the partition function of a statistical system can be related to the vacuum expectation value of the time ordered product of the observable quantities of the corresponding field theoretic model. Hence a generalization of ordinary scale invariance in the form of conformal invariance is focussed upon. This principle is very suitably applicable, in the case of two dimensional statistical models undergoing second order phase transitions at criticality. The conformal anomaly specifies the universality class to which these models belong. From an evaluation of the partition function, the free energy at criticality is computed, to determine the conformal anomaly of these models. The conformal anomaly for all the models considered here are in good agreement with the predicted values. / Source: Dissertation Abstracts International, Volume: 52-10, Section: B, page: 5329. / Major Professor: Dennis W. Duke. / Thesis (Ph.D.)--The Florida State University, 1991.

To gain understanding of the Higgs-fermion sector of the standard model, we study the one-component $Z\sb2$ symmetric and the four-component $O(4)$ symmetric scalar models coupled to staggered fermions using the hybrid Monte Carlo algorithm. We map out the phase diagrams, and show that the $Z\sb2$ model has a tree level perturbative behaviour at all points in the broken phase. The $O(4)$ model on the other hand is shown to have two characteristically different behaviours; one for large Yukawa couplings where the fermions get infinitely heavy and decouple in the continuum limit, and one for small Yukawa couplings where the fermions remain light. For very small Yukawa couplings the fermions show the expected tree level perturbative behaviour and for larger values the influence of the fermions becomes substantial. After estimating the finite size effects at small Yukawa couplings we make relatively accurate measurements of the scalar mass and wave function renormalization constants at the point $\kappa$ = 0.0 and y = 0.85-0.95. Even though this is not the largest value possible for the Yukawa coupling we are able to show that the bound of the Higgs mass will move up significantly, from around 600 GeV to around 900 GeV, by including fermions in the model. Likewise we show that a bound can be put on the fermion mass, around 200 GeV. The largest value of the bare Yukawa coupling is obtained at rather large negative $\kappa$. Due to bad convergence rates in the inversion of the fermion matrix, which is needed in the updating procedure, this region has not been possible to investigate. / Source: Dissertation Abstracts International, Volume: 53-03, Section: B, page: 1424. / Major Professors: Urs M. Heller; Dennis Duke. / Thesis (Ph.D.)--The Florida State University, 1992.

The results presented in this dissertation are based on Fermilab MPS experiment E580. This experiment was designed to study states which decay into two neutral strange particles. Copious K*('(+OR-)) production was observed in the K(,s)('0) K(,s)('0) + X data sample. Evidence for narrow resonances at 1.87 GeV/c('2) was clearly seen in both K(,s)('0) K*('+) and K(,s)('0) K*('-) mass spectra. These signals were interpreted as Cabibbo suppressed decay modes of D('(+OR-)) mesons. This is the first observation of this particular decay mode. The measured D('(+OR-)) decay ratio of (K(,s)('0) K*('(+OR-))) / (K(,s)('0) K(,s)('0) PI('(+OR-))) is (0.78 (+OR-) 0.06). The x(,F) distributions for the D('-) from both Cabibbo suppressed and Cabibbo favored (K(,s)('0) 3PI) modes exhibit definite forward production. / Source: Dissertation Abstracts International, Volume: 46-04, Section: B, page: 1212. / Thesis (Ph.D.)--The Florida State University, 1985.

Several computer simulations studying a variety of topics in statistical mechanics and lattice gauge theories are performed. / The first study describes a Monte Carlo simulation performed on Ising systems defined on Sierpinsky carpets of dimension between one and four. The critical coupling and the exponent $\gamma$ are measured as a function of dimension. The conclusions drawn from the study are that fractals of the Sierpinsky carpet type can be used to extrapolate statistical systems smoothly between integer dimension in the way given by the $\epsilon$-expansion. The Ising gauge theory in $d = 4 -\epsilon,$ for $\epsilon\to 0\sp+,$ is then studied by performing a Monte Carlo simulation for the theory defined on fractals. The study indicates that the first order phase transition of the $d = 4$ theory becomes second order for all $\epsilon\not= 0,$ implying that 4 may be identified as an upper critical dimension for abelian gauge theories. / A high statistics Monte Carlo simulation for the three-dimensional Ising model is presented for lattices of sizes $8\sp3$ to $44\sp3.$ All the data obtained agrees completely, within statistical errors, with the forms predicted by finite-size scaling. The simulations were made possible by developing a very high speed implementation of the Metropolis algorithm. A finite-size scaling study of the susceptibility at criticality gives ${\gamma\over\nu} = 1.964(3).$ / Finally, a method to estimate numerically the partition function of statistical systems is developed. The method is first applied to calculate the partition function of the three dimensional Ising model on lattices of size $5\sp3$ to $10\sp3.$ From a finite-size scaling of the zeros of these partition functions in the complex $\beta$ plane, the estimate $\nu = 0.6295(10)$ is obtained. A study done for the $Z(2)$ and $Z(8)$ gauge theories shows how one can obtain the order of the phase transition from the scaling of the zeros. The method is finally applied to the $SU(2)$ gauge theory. A line of zeros signaling the $g\sbsp{0}{2} = 0$ fixed point is observed. The study also shows that the lines of zeros of even a $2\sp4$ lattice are a qualitative signal to distinguish a potential phase transition from a crossover. / Source: Dissertation Abstracts International, Volume: 48-07, Section: B, page: 2008. / Thesis (Ph.D.)--The Florida State University, 1987.

The angular distribution of hadron pairs produced in the interaction of 800 GeV/c protons on targets of aluminium, beryllium, iron and tungsten have been measured, inferring the underlying dynamics of parton-parton scattering in these interactions. The transverse momentum hadron pairs with p$\sb{\rm T} <$ 2.0 GeV/c are studied in three charge states, (+ +), (+ $-$), ($- -$) covering the dihadron mass range of 7 to 15 GeV/c$\sp2$ and scattering angles up to cos $\theta\sp\*$ = 0.50. While the parton-parton angular distributions are shown to be independent of the target type, a small dependence on the charge state of the distributions is observed. These results are found to be generally consistent with the results of leading log QCD calculations. Unlike-sign charge state distributions for this experiment are found to deviate from low x dijet results as expected, and are found to be consistant with neutral dipion production results. / The cross section as a function of the parton-parton scattering angle for the three charge states is shown to vary linearly with the value of the atomic weight. The ratio of the cross sections for different charge states as a function of the parton-parton scattering angle is also found to compare favorably with the predictions of leading log QCD calculations. / Source: Dissertation Abstracts International, Volume: 52-08, Section: B, page: 4269. / Major Professor: Vasken Hagopian. / Thesis (Ph.D.)--The Florida State University, 1991.

The asymmetry in the angular distribution of hadronic events produced in the reaction $e\sp+e\sp- \to Z\sp\circ\to$ hadrons at center of mass energies near the mass of the $Z\sp\circ$ is studied. The data used in the analysis were taken at the European Center for Nuclear Research (CERN) from September 1989-August 1990. / The detector was a large multicomponent system consisting of a central Time Projection Chamber, full electromagnetic and hadronic calorimetry, additional tracking near the interaction region, and luminosity monitors. It provided good charged track reconstruction and momentum resolution. / The charge asymmetry is measured through the mean charge flow, $Q\sb{FB}$ averaged over all events, where $Q\sb{FB}$ = $Q\sb{F}$ $-$ $Q\sb{B}$ is the difference between the momentum weighted charges in the forward and backward hemispheres. / A fit to the value of $\langle Q\sb{FB}\rangle$ yields a measurement of $\rm sin\sp2 \theta\sb{W}(M\sbsp{Z}{2})$ = 0.2300 $\pm$ 0.0036(stat.) $\pm$ 0.0015(exp.sys.) $\pm$ 0.0021(theor.sys.), which compares well with values obtained by other methods. Using quark coupling measurements from previous experiments, a value for the electron left-right asymmetry of ${\cal A}\sb{\rm e}$ = 0.122$\sbsp{-0.026}{+0.046}$ is obtained. This result can also be expressed as a measurement of the ratio of the electron vector and axial couplings, / Source: Dissertation Abstracts International, Volume: 52-06, Section: B, page: 3120. / Major Professor: David Levinthal. / Thesis (Ph.D.)--The Florida State University, 1991.

Results are presented on neutral production in (pi)-p interactions at 250 GeV/c. The data was obtained from a 46,000 picture exposure of the liquid hydrogen filled 15 foot bubble chamber at Fermi National Accelerator Laboratory. A total of 22,330 beam interactions and 25,110 candidate gammas were found in the film. Semi-inclusive cross sections were obtained for 2 through 24 charged particle topologies. The production vertex and all associated gammas were measured in 45% of the interactions having one or more candidate gammas. The neutral pion multiplicity distribution was obtained as a function of charged topology and for all charged topologies using the scan information on gamma production. The total neutral pion multiplicity was found to be equivalent to 1/2 the produced charged pion multiplicity. The total (charged plus neutral) non-strange multiplicity distribution was obtained for 0 to 15 particles. The total multiplicity was found to display evidence of oscillatory behaviour with the final state more likely to contain even numbers of particles than odd. Neutral pion longitudinal and transverse momentum and rapidity distributions were obtained from the measured gamma momentum distributions. This experiment was the first hadrom study in the FNAL 15 foot bubble chamber and presents the first data on semi-inclusive neutral pion and total multiplicities at high energies. / Source: Dissertation Abstracts International, Volume: 43-12, Section: B, page: 4030. / Thesis (Ph.D.)--The Florida State University, 1982.

From a sample of 30,400 two prong events the reaction (pi)('+) p (--->) (pi)('+) p (pi)('0) (pi)('0) at 15.7 GeV/c is studied. The data were taken at the SLAC 40'' hybrid bubble chamber with a segmented lead-glass wall placed downstream of the bubble chamber to detect photons and to trigger the bubble chamber upon a deposition of 8 GeV or more of energy. With information from the wall it is possible to reconstruct constrained events with two neutral pions. / The experimental setup and the use of the wall in reconstructing the (pi)('0)'s is described. Invariant masses are presented including the (pi)('0)(pi)('0) mass up to about 4 GeV. No new high mass neutral meson is seen. A van Hove analysis is performed, showing considerable pion diffractive events and production of (DELTA)('++)(1232), f('0)(1270), and (rho)(770). / Events with a (DELTA)('++)(1232) present are isolated and investigated. The cross section for the reaction (pi)('+) p (--->) (DELTA)('++) f('0) (f('0) (--->) (pi)('0)(pi)('0)) is determined to be 25.8 (+OR-) 3.4 microbarns. A moments analysis and amplitude analysis are performed, showing that only S and D wave contributed to the cross section. There is no evidence for the narrow (epsilon)(700), nor for the recently reported f'(1800). / An OPE model calculation is made and compared with data using phase shifts measurements from other experiments. When using phase shifts from Biswas (1981) the model underestimated the cross section below m((pi)('0)(pi)('0)) = 1 GeV, while with phase shifts from Estabrooks and Martin (1974) the model is consistent with the data. / Source: Dissertation Abstracts International, Volume: 44-01, Section: B, page: 0211. / Thesis (Ph.D.)--The Florida State University, 1983.

Source: Dissertation Abstracts International, Volume: 31-09, Section: B, page: 5540. / Thesis (Ph.D.)--The Florida State University, 1970.