A Search for Relativistic Magnetic Monopoles with the IceCube 22-String Detector
Christy, Brian John
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Magnetic monopoles are particles which act as a source for divergent magnetic fields, equivalent to a proton's electric field. Beyond simply adding the final symmetry to Maxwell's equations, their existence would solve numerous outstanding problems in the particle physics community. However, no conclusive evidence for their existence has been found. Magnetic monopoles possess many unique characteristics that allow for detection from a variety of experimental methods. One property is the large scaling of the Cherenkov radiation (∼ 8300) compared to electrically charged particles. Magnetic monopoles are postulated to be extremely heavy (∼ 10<super>4</super>−10<super>17</super> GeV). However, they would be topologically stable and accelerated via magnetic field lines throughout the universe, potentially reaching energies ∼ 10<super>15</super> GeV. Therefore, searches for relativistic magnetic monopoles incident on Earth are an important piece to the overall experimental search. The IceCube neutrino observatory, located at the South Pole, offers a novel environment to search for these particles. IceCube is a km<super>3</super grid of light sensors buried deep within the Antarctic Ice Shelf and represents the most colossal neutrino telescope in the world. The large instrumented volume and relatively clear glacial ice allows for a significant improvement in sensitivity to the bright tracks relativistic magnetic monopoles would exhibit. The main background comes from large muon bundles produced in air showers generated by the highest energy cosmic rays. The depth of the detector allows for a limited rejection of these events from the Southern Hemisphere, while the Earth acts as an opaque shield to these events traveling from the Northern Hemisphere. In contrast, a large range of potential magnetic monopole masses and energies considered (M & 10<super>7</super> GeV, E & 10<super>11</super> GeV) can travel completely through the Earth while remaining relativistic. This dissertation details the first search performed for these relativistic magnetic monopoles with IceCube data. The data is from 2007, when IceCube operated as a partially completed detector with an instrumented volume of ∼0.2 km<super>3</super>. It considers monopoles at four discrete speeds: β = 0.76, 0.8, 0.9, 0.995, ranging from just above the Cherenkov threshold in ice to a boost factor of 10. Discrimination between a potential magnetic monopole signal and background is achieved by considering the brightness and direction of the event. After an initial search revealed deficiencies in the simulated background model, a more conservative analysis produces limits that are ∼ 10 x better than previous searches. The final limits are then transformed to be a limit on an isotropic flux at the Earth's surface, due to the dependence on direction to the overall sensitivity of the analysis.