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  • Scott, Pat, 1982- (författare)
  • Searches for Particle Dark Matter Dark stars, dark galaxies, dark halos and global supersymmetric fits
  • 2010
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • <p>The identity of dark matter is one of the key outstanding problems in both particle and astrophysics. In this thesis, I describe a number of complementary searches for particle dark matter. I discuss how the impact of dark matter on stars can constrain its interaction with nuclei, focussing on main sequence stars close to the Galactic Centre, and on the first stars as seen through the upcoming James Webb Space Telescope. The mass and annihilation cross-section of dark matter particles can be probed with searches for gamma rays produced in astronomical targets. Dwarf galaxies and ultracompact, primordially-produced dark matter minihalos turn out to be especially promising in this respect. I illustrate how the results of these searches can be combined with constraints from accelerators and cosmology to produce a single global fit to all available data. Global fits in supersymmetry turn out to be quite technically demanding, even with the simplest predictive models and the addition of complementary data from a bevy of astronomical and terrestrial experiments; I show how genetic algorithms can help in overcoming these challenges.</p>
  • Birgersson, Evert, et al. (författare)
  • Binary fission-fragment yields from the reaction 251Cf(nth, f)
  • 2005
  • Ingår i: Nuclear fission and fission-product spectroscopy : 3rd international workshop on nuclear fission and fission-product spectroscopy. - American Institute of Physics. - 0-7354-0288-4 ; s. 349-352
  • Konferensbidrag (refereegranskat)abstract
    • <p>The recoil mass spectrometer LOHENGRIN of the Laue-Langevin Institute, Grenoble has been used to measure the light fission-fragment mass yield and kinetic energy distributions from neutron-induced <sup>252</sup>Cf*, using <sup>251</sup>Cf as target material. ©2005 American Institute of Physics</p>
  • Birgersson, Evert, et al. (författare)
  • Light fission-fragment mass distribution from the reaction 251Cf(nth, f)
  • 2007
  • Ingår i: Nuclear Physics A. - Amsterdam : Elsevier. - 0375-9474 .- 1873-1554. ; 791:1-2, s. 1-23
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>For mass numbers A = 80 to 124 the recoil mass spectrometer LOHENGRIN of the Institute Laue-Langevin in Grenoble was used to measure with high resolution the light fission-fragment mass yields and kinetic energy distributions from thermal-neutron induced fission of 252Cf* for the first time, using 251Cf as target material. The obtained mean light fragment mass AL = (107 ± 2) and the corresponding mean kinetic energy Ek,L = (103±2) MeV are within the expected trend. Emission yields around A = 115 are enhanced and the corresponding mean kinetic energy is higher compared to spontaneous fission of 252Cf. This could be explained by the existence of an additional super-deformed fission mode.</p>
  • Oberstedt, Andreas, et al. (författare)
  • Energy degrader technique for light-charged particle spectroscopy at LOHENGRIN
  • 2007
  • Ingår i: Nuclear Instruments and Methods in Physics Research Section A : Accelerators, Spectrometers, Detectors and Associated Equipment. - Amsterdam : Elsevier. - 0168-9002 .- 1872-9576. ; 570:1, s. 51-54
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>The recoil mass-separator LOHENGRIN at Institute Laue-Langevin was originally designed for the spectrometry of binary fission fragments. Nevertheless, it was also used in the past for measuring light-charged particles from ternary fission. However, due to the electric field settings the energy distribution of the lightest particles was not completely accessible, which made the determination of mean kinetic energies, widths and, hence, emission yields difficult. In this paper we present an energy degrader technique that allows for the measurement of the entire energy spectrum of even the lightest ternary particles with LOHENGRIN.</p>
  • Oberstedt, Andreas, et al. (författare)
  • Identification of a Shape Isomer in <sup>235</sup>U
  • 2007
  • Ingår i: Physical Review Letters. - The American Physical Society. - 0031-9007 .- 1079-7114. ; 99:4, s. 1-4
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>The shape isomer in 235U has been searched for in a neutron-induced fission experiment on 234U, which was performed at the isomer spectrometer NEPTUNE of the EC-JRC IRMM. A neutron source, with a tunable pulse frequency in the Hz to kHz range and its individually adjustable neutron pulse width in connection with an appropriate detector system turned out to be the ideal instrument to perform an isomer search, when decay half-lives above 100 us are expected. From the delayed fission events observed for two different NEPTUNE settings and at mean incident neutron energies En = 0.95 and 1.27 MeV the isomeric fission half-life could be determined to be T_1/2 = (3.6 ± 1.8) ms. The corresponding cross section was determined to sigma_if = (10 ± 8) ub. With these results an experimental confirmation for the existence of a superdeformed shape isomer in odd-uranium isotopes is given for the first time.</p>
  • Waltersson, Erik, 1979-, et al. (författare)
  • Controlled operations in a strongly correlated two-electron quantum ring
  • 2009
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - American Physical Society. - 1098-0121 .- 1550-235X. ; 79:11, s. 115318
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>We<sup> </sup>have analyzed the electronic spectrum and wave-function characteristics of a<sup> </sup>strongly correlated two-electron quantum ring with model parameters close to<sup> </sup>those observed in experiments. The analysis is based on an<sup> </sup>exact diagonalization of the Hamiltonian in a large B-spline basis.<sup> </sup>We propose a qubit pair for storing quantum information, where<sup> </sup>one component is stored in the total electron spin and<sup> </sup>one multivalued “quMbit” is represented by the total angular momentum.<sup> </sup>In this scheme the controlled-NOT quantum gate is demonstrated with<sup> </sup>near 100% fidelity for a realistic far-infrared electromagnetic pulse.</p>
  • Bergeås Kuutmann, Elin, 1980- (författare)
  • Calibration of the ATLAS calorimeters and discovery potential for massive top quark resonances at the LHC
  • 2010
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • <p>ATLAS is a multi-purpose detector which has recently started to take data at the LHC at CERN. This thesis describes the tests and calibrations of the central calorimeters of ATLAS and outlines a search for heavy top quark pair resonances.The calorimeter tests were performed before the ATLAS detector was assembled at the LHC, in such a way that particle beams of known energy were targeted at the calorimeter modules. In one of the studies presented here, modules of the hadronic barrel calorimeter, TileCal, were exposed to beams of pions of energies between 3 and 9 GeV. It is shown that muons from pion decays in the beam can be separated from the pions, and that the simulation of the detector correctly describes the muon behaviour.</p> <p>In the second calorimeter study, a scheme for local hadronic calibration is developed and applied to single pion test beam data in a wide range of energies, measured by the combination of the electromagnetic barrel calorimeter and the TileCal hadronic calorimeter. The calibration method is shown to provide a calorimeter linearity within 3%, and also to give a reasonable agreement between simulations and data.</p> <p>The physics analysis of this thesis is the proposed search for heavy top quark resonances, and it is shown that a narrow uncoloured top pair resonance, a <em>Z'</em>, could be excluded (or discovered) at 95% CL for cross sections of 4.0±1.6 pb (in the case of <em>M</em>=1.0 TeV/c<sup>2</sup>) or 2.0±0.3 pb (<em>M</em>=2.0 TeV/c<sup>2</sup>), including systematical uncertainties in the model, assuming √<em>s</em> = 10 TeV and an integrated luminosity of 200 pb<sup>-1</sup>. It is also shown that an important systematical uncertainty is the jet energy scale, which further underlines the importance of hadronic calibration.</p>
  • Birgersson, Evert, et al. (författare)
  • Properties of the reaction 238U(n, f) at the vibrational resonances
  • 2009
  • Ingår i: Nuclear Physics A. - Amsterdam : Elsevier. - 0375-9474 .- 1873-1554. ; 817:1-4, s. 1-34
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>Recent fission cross-section calculations for the reaction 238U(n, f ), based on an extended statistical model, predict a significant change of fission fragment properties, such as the mean mass by A = 1.5 and a notable increase in total kinetic energy in the region of the vibrational resonance at an incident neutron energy En = 0.9 MeV. This model includes individual fission cross-sections by the asymmetric standard 1 (S1) and standard 2 (S2) as well as the symmetric super-long (SL) mode. In order to verify the model predictions, a dedicated experiment on 238U has been carried out to measure fission-fragment mass yield distributions for incident neutron energies from En = 2.0 MeV down to 0.9 MeV, where the fission characteristics at the vibrational resonance at En = 0.9 MeV were investigated for the first time. The previously reported distinct structure in the angular anisotropy around En = 1.2 and 1.6 MeV wasobserved at En = 0.9 MeV as well. The predicted large changes in fission fragment mass yield and total kinetic energy could not be confirmed. In the resonance the mean total kinetic energy is only about 0.5 MeV higher than at En = 1.8 MeV. At the same time, a slight decrease of the mean heavy fragment mass was observed, probably indicating a slightly increased contribution of the S1 fission mode.</p>
  • Lundström, Erik, 1980- (författare)
  • Phenomenology of Inert Scalar and Supersymmetric Dark Matter
  • 2010
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • <p>While the <em>dark matter</em> has so far only revealed itself through the gravitational influence it exerts on its surroundings, there are good reasons to believe it is made up by WIMPs – a hypothetical class of heavy elementary particles not encompassed by the Standard Model of particle physics.</p> <p>The Inert Doublet Model constitutes a simple extension of the Standard Model Higgs sector. The model provides a new set of scalar particles, denoted <em>inert</em> scalars because of their lack of direct coupling to matter, of which the lightest is a WIMP dark matter candidate.</p> <p>Another popular Standard Model extension is that of <em>supersymmetry</em>. In the most minimal scenario the particle content is roughly doubled, and the lightest of the new supersymmetric particles, which typically is a <em>neutralino</em>, is a WIMP dark matter candidate.</p> <p>In this thesis the phenomenology of <em>inert scalar</em> and <em>supersymmetric</em> dark matter is studied. Relic density calculations are performed, and experimental signatures in indirect detection experiments and accelerator searches are derived.</p> <p>The Inert Doublet Model shows promising prospects for indirect detection of dark matter annihilations into monochromatic photons. It is also constrained by the old LEP II accelerator data.</p> <p>Some phenomenological differences between the Minimal Supersymmetric Standard Model and a slight extension, the Beyond the Minimal Supersymmetric Standard Model, can be found. Also, supersymmetric dark matter models can be detected already within the early LHC accelerator data.</p>
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