No description available.

Despite many years of research dedicated to elucidating the conditions in which cosmic rays (CRs) are accelerated, there is still great uncertainty about exactly how such particles are accelerated up to energies of 1 TeV (1 TeV= 10¹² eV) and well beyond. Additionally, there is also great uncertainty about the structure and amplitude of the Galactic magnetic field which necessarily has a great impact upon the movement and interaction of CRs in the Galaxy. This thesis deals with a number of ways in which Gigahertz (GHz) frequency radio continuum observations can be used with GeV–TeV γ-ray observations to explore (i) the CR spectrum and (ii) the magnetic field amplitude in the Galaxy. An accurate knowledge of the CR spectrum and amplitude of the magnetic field has important consequences for a wide range of phenomena, such as particle acceleration and even star formation within the Galaxy. We present a simple static, single-zone model of secondary electron and positron production from CR protons and heavier nuclei interacting with ambient matter. We then apply this model, assuming a local CR spectrum, to predict the synchrotron emission from two cold, dense, massive molecular cores which are relatively nearby using a prescription for the magnetic field which scales as the (approximate) square-root of the hydrogen number density. Radio continuum observations with the Australia Telescope Compact Array (ATCA) are then used to search for this emission and, due to the lack of detection, upper limits to the magnetic fields within these cores are obtained. We find that these limits are not inconsistent with the prescription used in the theoretical modeling. We also present observations of a giant molecular cloud located in the Galactic centre (GC) region, Sagittarius B2 (Sgr B2), chosen because of the expectation of a higher CR flux (than that observed at the top of the earth’s atmosphere). Based on previous work, the simple model presented in this thesis is then extended to include effects of CR diffusion into the Sgr B2 cloud parameterized by a “diffusion transport suppression” factor (and based on a molecular distribution – obtained from NH₃ spectral line emission studies – that can modeled as a three-dimensional Gaussian distribution). Our results show that the complex nature of the environment severely hampers the separation of the thermal and non-thermal emission so that no spectral, polarized or morphological evidence is found for non-thermal emission due to secondary electrons and positrons. Analysis of the radial brightness distribution from the centre of the main complex of Sgr B2 allowed us to place limits on the diffusion of GeV energy CRs into the cloud. This leads to a relative deficit of CRs at the centre of the cloud and a morphology which is reminiscent of a ‘limb-brightening’ of synchrotron emission from secondary electrons and positrons. This is in contrast to to the TeV energy γ-rays from which a good correlation with molecular matter in the GC region is observed. This is interpreted by us as evidence of the exclusion of GeV energy CRs from the densest molecular environments in this region, whilst the TeV (or higher) CRs are able to freely penetrate these regions leading to the γ-ray -molecular line emission correlation observed by the HESS telescopes. Serendipitously, observations of this region uncovered evidence of non-thermal emission from a source to the south of the main complex of emission within Sgr B2. Analysis of archival XMM-Newton X-ray observations revealed an X-ray source located approximately 20” from the non-thermal radio source whose spectrum is strongly suggestive of a SNR. The non-thermal radio spectrum, X-ray source and spectrum were then used in concert with NH3 line emission to argue that this source is a SNR of approximately 3000 years of age which had exploded in this dense region. A large gradient in the NH₃ line emission towards the X-ray source suggests that any SNR shell would expand towards this region of lower density. Analysis of higher resolution 1720 MHz ATCA data revealed a weak source whose extension is coincident with the X-ray source. Finally, the observations of the Sgr B2 region were then expanded to explore the nature of the magnetic field amplitude on large scales in the region, of which there is a two orders of- magnitude uncertainty. Based on earlier work, which showed a large (6° x 2°) region of synchrotron emission at the GC, we assembled single-dish and interferometric observations of this region. The objective of this was to explore the possibility that a ‘spectral downturn’ existed at GHz frequencies, which is due to the gradual dominance towards lower energies of the bremsstrahlung cooling rate over the synchrotron cooling rate. After the removal of appropriate background and the consideration of limitations at GeV and TeV energies, we found significant statistical evidence for a spectral break at ~ 2 GHz, which implies a magnetic field amplitude of 100 μG in a density of ~ 100 cm ⁻³. An amplitude this high, on such large scales will have a large impact on processes such as particle acceleration, star-formation and gas-dynamics in the region. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1456598 / Thesis (Ph.D.) -- University of Adelaide, School of Chemistry and Physics, 2009

The luminosity system is an integral part of the DO detector that must be properly maintained to provide accurate luminosity measurements for physics analysis. After the addition of a readout layer to the silicon vertex detector in 2006, it was necessary to re-calculate the effective inelastic cross section to which the luminosity monitor is sensitive. The preliminary analysis showed that the luminosity constant did not change with the addition of the extra layer of silicon. A full study of the revised luminosity constant including a complete analysis of systematic uncertainties has been completed. The luminosity constant was determined to be sigmaeff = 48.3 +/- 1.9 +/- 0.6 mb, which reduces the DO contribution to the luminosity measurement uncertainty by almost 3%.

We report the result of a search for the pair production of the light supersymmetric partner of the top quark (t˜1) in 5.4+/-0.3 fb-1 of data from the DO detector at a pp¯ center-of-mass energy of 1.96 TeV at the Fermilab Tevatron collider. The scalar top quarks are assumed to decay into a b quark, a charged lepton and a scalar neutrino ( n&d5; ), and the search is performed in the electron plus muon final state. No significant excess of events above the standard model prediction is detected and new exclusion limits at the 95% C.L. are set for a portion of the ( mt&d5;1,m n&d5; ) mass plane.

Charged particle tracking and identification are important elements of any elementary particle physics experiment. Transition radiation is often used to separate electrons from heavier charged particles. This thesis describes a combined tracking and transition radiation detector well suited to the high rate environment of the Superconducting Super Collider (SSC). In the proposed "Electrons Muons Partons with Air Core Toroids" (EMPACT) detector at the SSC the straw tubes with 4 mm diameter filled with 50-50 Xenon-CO₂ and polyethylene radiation foams are selected for the tracking system. The principles of operation of proportional chambers have been studied. The size of the tube is related to the characteristics of the filling gas and the desired occupancy.

While we may know the overall quantum numbers of a given meson state and that such a state is necessarily a color singlet, we do not know a priori the relative spin and color alignments of the constituents: the quarks, antiquarks, and gluons. The overall meson wavefunction may have contributions from different spin-color configurations: one where the quark and antiquark alone account for the spin of the meson; or another where a gluon excitation also contributes to the total spin (a hybrid state), while helping to form the color singlet. The determination of the relative contributions of each these configurations to the overall meson state is the focus of this work. We use the lattice formulation of quantum chromodynamics (QCD) and we restrict our analysis to the limit of heavy quark masses. We are therefore able to use a non-relativistic approximation for the quark and antiquark Hamiltonians (NRQCD). This provides the additional separation of the spin- and orbital-angular-momentum degrees of freedom of the quarks. We therefore have a clear separation of basis states where the meson spin is carried by only the quark and antiquark spins, their relative orbital motion, or a combination of the two; and also the state where a gluon excitation is needed, along with the quark and antiquark, to form the correct quantum numbers. Using only the static and kinetic terms of the heavy-quark Hamiltonian we create meson-like correlators with the same quantum numbers, but with different color-spin configurations. From these correlators we extract the masses and amplitudes which form the basis of a two-state system. We then apply the lowest-order spin-dependent interaction at various intermediate time slices to form correlators between different configurations. From these "mixed" correlators we extract the off-diagonal matrix elements of our two-state Hamiltonian. Diagonalizing this Hamiltonian, we find the relative contribution of each spin-color configuration to the true heavy-meson ground state.

We have measured the charge asymmetry of muons produced in W boson decay as a function of muon pseudorapidity. The W bosons were produced in pp̄ collisions at √s = 1.8 TeV at the Fermilab Tevatron and recorded by the D⊘ detector during the run period 1992-1993 (run 1A) and 1994-1995 (run 1B). The combined data for both periods consists of 8831 W → μν decays with / ημ / < 1.0 selected from events corresponding to an integrated luminosity of 61.9 pb⁻¹ and 664 decays with 1.0 ≤ / ημ / < 1.6 corresponding to an integrated luminosity of 44.5 pb⁻¹.

We have measured the b-quark production cross section for / y / < 1 using a sample of muons with associated jets collected with the D⊘ detector in pp̄ collisions at √s = 630 GeV at the Fermilab Tevatron. The measured b-quark cross section is consistent in shape with O(α³s) QCD predictions, but exceeds them in normalization by roughly a factor of 2.5.

Calorimeter has been an essential element of High Energy Physics Experiment for decades. As beam energies of hadron colliders reached the multi-TeV range, hermeticity of the calorimetric system became a high priority issue. Additional requirements arose from increased luminosity. The Forward Calorimeter (covering rapidity η >3) must to provide high quality measurements of hadronic jets (energy and position) at extremely high rate and at the same time withstand a harsh radiation environment. The Liquid Argon Tube Forward Calorimeter was developed at the University of Arizona to fulfill those requirements. Prototypes of the electromagnetic section (15X₀, later 25X₀) were tested at BNL and CERN secondary beams in 1993 and 1995. Data acquired in those tests allowed us to study such vital parameters of the calorimeter as response uniformity, energy and position resolution. An energy range from 2 GeV to 200 GeV and angles from 0.6° to 5.6° were covered. Observed results (together with extensive Monte-Carlo simulation studies of the Forward Region) allowed the Liquid Argon Tube Calorimeter to be chosen among several competing designs as the Baseline for the Forward Calorimeter of the ATLAS multi-purpose detector at the LHC (CERN).

With our newly proposed dynamical Higgs mechanism and Quantum Induction programme, Higgs mass is predicted at M(H) ≈ 190 GeV by using our modified renormalization group equations. The same procedure also explains the top quark mass correctly.