| 1. |
- Burgman, Alexander, 1991-
(författare)
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Bright Needles in a Haystack : A Search for Magnetic Monopoles Using the IceCube Neutrino Observatory
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The IceCube Neutrino Observatory at the geographic South Pole is designed to detect the light produced by the daughter-particles of in-ice neutrino-nucleon interactions, using one cubic kilometer of ice instrumented with more than 5000 optical sensors.Magnetic monopoles are hypothetical particles with non-zero magnetic charge, predicted to exist in many extensions of the Standard Model of particle physics. The monopole mass is allowed within a wide range, depending on the production mechanism. A cosmic flux of magnetic monopoles would be accelerated by extraterrestrial magnetic fields to a broad final velocity distribution that depends on the monopole mass.The analysis presented in this thesis constitutes a search for magnetic monopoles with a speed in the range [0.750;0.995] in units of the speed of light. A monopole within this speed range would produce Cherenkov light when traversing the IceCube detector, with a smooth and elongated light signature, and a high brightness.This analysis is divided into two main steps. Step I is based on a previous IceCube analysis, developed for a cosmogenic neutrino search, with similar signal event characteristics as in this analysis. The Step I event selection reduces the acceptance of atmospheric events to lower than 0.1 events per analysis livetime. Step II is developed to reject the neutrino events that Step I inherently accepts, and employs a boosted decision tree for event classification. The (astrophysical) neutrino rate is reduced to 0.265 events per analysis livetime, corresponding to a 97.4 % rejection efficiency for events with a primary energy above 1E+5 GeV.No events were observed at final analysis level over eight years of experimental data. The resulting upper limit on the magnetic monopole flux was determined to 2.54E–19 per square centimeter per second per steradian, averaged over the covered speed region. This constitutes an improvement of around one order of magnitude over previous results.
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| 2. |
- Olivo, Martino
(författare)
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Neutrino emission from high-energy component gamma-ray bursts
- 2010
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Gamma-ray bursts (GRBs) are brief and sudden explosions radiating most of their energy in the soft γ-ray band ( 100 keV). In the context of multimessenger astroparticle physics recent observations of GRBs provide an excellent benchmark for testing theoretical models of high energy emission mechanisms. Acceleration of hadrons in the engine is expected to produce high energy neutrinos and gamma-rays simultaneously via π±/π0 decays, thus reinforcing the motivation for coincident searches in km3 neutrino telescopes. The Waxman-Bachall spectra and the corresponding expected neutrino rates in IceCube are derived here for GRB090510 amd GRB090902B recently detected by the Fermi Large Area Telescope. The implications of the significant detection of deviations from the Band function fit in photon spectra and a model that explains these extra-components in terms of π0-decay photons are presented here and the relevance to neutrino astronomy is shown.
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| 3. |
- Ström, Rickard, 1985-
(författare)
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Exploring the Universe Using Neutrinos : A Search for Point Sources in the Southern Hemisphere Using the IceCube Neutrino Observatory
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Neutrinos are the ideal cosmic messengers, and can be used to explore the most powerful accelerators in the Universe, in particular the mechanisms for producing and accelerating cosmic rays to incredible energies. By studying clustering of neutrino candidate events in the IceCube detector we can discover sites of hadronic acceleration. We present results on searches for point-like sources of astrophysical neutrinos located in the Southern hemisphere, at energies between 100 GeV and a few TeV. The data were collected during the first year of the completed 86-string detector, corresponding to a detector livetime of 329 days. The event selection focuses on identifying events starting inside the instrumented volume, utilizing several advanced veto techniques, successfully reducing the large background of atmospheric muons. An unbinned maximum likelihood method is used to search for clustering of neutrino-like events. We perform a search in the full Southern hemisphere and a dedicated search using a catalog of 96 pre-defined known gamma-ray emitting sources seen in ground-based telescopes. No evidence of neutrino emission from point-like sources is found. The hottest spot is located at R.A. 305.2° and Dec. -8.5°, with a post-trial p-value of 88.1%. The most significant source in the a priori list is QSO 2022-077 with a post-trial p-value of 14.8%. In the absence of evidence for a signal, we calculate upper limits on the flux of muon-neutrinos for a range of spectra. For an unbroken E-2 neutrino spectrum, the observed limits are between 2.8 and 9.4×10-10 TeV cm-2 s-1, while for an E-2 neutrino spectrum with an exponential cut-off at 10 TeV, the observed limits are between 0.6 and 3.6×10-9 TeV cm-2 s-1.
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| 4. |
- Taavola, Henric, 1983-
(författare)
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Dark Matter in the Galactic Halo : A Search Using Neutrino Induced Cascades in the DeepCore Extension of IceCube
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A search for Weakly Interacting Massive Particles (WIMPs) annihilating in the dark matter halo of the Milky Way was performed, using data from the IceCube Neutrino Observatory and its low-energy extension DeepCore. The data were collected during one year between 2011 to 2012 corresponding to 329.1 days of detector livetime. If WIMPs in the dark matter halo undergo pairwise annihilation they may produce a neutrino signal detectable at the Earth. Assuming annihilation into bb, W+W-, τ+τ-, μ+μ-, νν and a neutrino flavor ratio of 1:1:1 at the detector, cascade events from all neutrino flavors were used to search for an excess of neutrinos matching a dark matter signal spectrum. Two dark matter density profiles for the halo were used; the cored Burkert profile and the cusped NFW profile. No excess of neutrinos from the Galactic halo was observed, and upper limits were set for the thermally averaged product of the WIMP self-annihilation cross section and velocity, <σAv>, in the WIMP mass range 30 GeV to 10 TeV. For the bb annihilation channel and the NFW halo profile, the 90% C.L. upper limits are 9.03×10-22 cm3 s-1 for the mass WIMP 100 GeV and 4.08×10-22 cm3 s-1 for the WIMP mass 3000 GeV. The corresponding upper limits for the μ+μ- annihilation channel are 4.40×10-23 cm3 s-1 and 3.20×10-23 cm3 s-1.
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| 5. |
- Unger, Elisabeth
(författare)
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The Extremes of Neutrino Astronomy : From Fermi Bubbles with IceCube to Ice Studies with ARIANNA
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Fermi bubbles are extended regions of hard gamma-ray emission which were discovered with Fermi-LAT data to exist above and below the Galactic Center. In order to explain the origin of the gamma-rays, different theories are proposed. In particular, within hadronic models, highly-accelerated cosmic rays interact with interstellar matter and create the observed gamma-rays and in addition neutrinos. Data from the neutrino detector IceCube was analyzed using a maximum likelihood method. An upper limit on the possible neutrino flux from the Fermi bubbles at energies between 10 GeV and 200 GeV was determined.While this analysis is performed with the lowest energies IceCube can reach, the ARIANNA (Antarctic Ross Ice-shelf ANtenna Neutrino Array) experiment has the goal to detect the highest energy neutrinos by measuring radio wave radiation produced by their interaction products in the ice. With ARIANNA the propagation of radio waves in the firn (packed snow) of the Ross Ice Shelf was investigated. According to the classical approach the radio waves, produced in the firn, are supposed to bend down because of the changing density, and therefore changing refractive index, an effect which is called “shadowing”. Evidence that the waves can travel horizontally over a long distance will be presented. The horizontally propagating signals between two boreholes and to the ARIANNA stations were analyzed and characterized. Analyses were performed under two hypotheses to determine attenuation lengths for horizontal propagation signals. The results showed attenuation lengths between 310 m ± 83 m and 651 m ± 270 m, depending on the assumed hypothesis and performed analysis. In addition unexpected signals consistent with radio waves propagating along the firn surface, here called pre-pulses, were observed and characterized.
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| 6. |
- Preston, Markus, 1989-
(författare)
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Developments for the FPGA-Based Digitiser in the PANDA Electromagnetic Calorimeters
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The strong interaction between quarks and gluons is one of the fundamental interactions described by the standard model of particle physics. Systems of quarks bound together by the strong interaction are known as hadrons, of which the proton and the neutron are the most common examples. The theoretical framework of quantum chromodynamics (QCD) is used to describe the strong interaction, but becomes increasingly difficult to use as the distance between the interacting particles increases. On the length scales relevant for hadrons, for instance, non-perturbative approaches to QCD have to be used. Experimental data are needed to verify these approaches. PANDA is one of the four experimental pillars of the upcoming FAIR facility in Darmstadt, Germany. In PANDA, an antiproton beam with a momentum between 1.5 and 15 GeV/c will interact in a hydrogen or nuclear target, allowing studies of various aspects of non-perturbative QCD. Motivated by the high interaction rates and the diverse physics goals of the experiment, a triggerless readout approach will be employed. In this approach, each detector subsystem will be equipped with intelligent front-end electronics that independently identify signals of interest in real time. In the electromagnetic calorimeter, FPGA-based digitiser modules will be used for this task. The high-radiation environment in PANDA will pose a challenge to these modules, due to both potential radiation damage and high signal rates from the calorimeter. In this thesis, these issues are addressed. First, the results from experimental measurements and Monte Carlo modelling of radiation-induced single event upsets in the FPGA are described. These studies have allowed predictions of the rate of single event upsets during operation of PANDA. Secondly, a newly developed algorithm for real-time processing of calorimeter signals in an FPGA at high pile-up rates is described. This algorithm provides a significant improvement in the time resolution of the calorimeter and allows reconstruction of the pulse height and timing of piled-up detector signals.
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| 7. |
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