Bright Needles in a Haystack : A Search for Magnetic Monopoles Using the IceCube Neutrino Observatory

• Main Author: Burgman, Alexander
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Uppsala universitet, Högenergifysik 2020
• Subjects: magnetic monopole; IceCube; astroparticle physics; neutrino telescope; Subatomic Physics; Subatomär fysik; Astronomy; Astrophysics and Cosmology; Astronomi; astrofysik och kosmologi; Haystack; South Pole; South pole
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-425610

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.