IceCube Neutrinos: from Oscillations to PeV-Energy Events
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PARTICLES AND FIELDS
IceCube Neutrinos: from Oscillations to PeV-Energy Events Francis Halzen
Received: 25 January 2013 © Sociedade Brasileira de F´ısica 2013
Abstract With IceCube and its low-energy extension DeepCore, a neutrino detector with an energy reach from tens of gigaelectronvolt to exaelectronvolt has been commissioned. It measures the atmospheric neutrino spectrum from the lower energies where neutrinos oscillate to energies as large as 100 TeV with a statistic of more than 100,000 events per year. The initial results suggest that IceCube can measure the oscillation parameters in an energy range that exceeds existing observations by 1 order of magnitude, thus opening a new window on neutrino physics. We emphasize the search for sterile neutrinos particularly relevant to cosmology. We also discuss the first observation of (PeV) petaelectronvolt-Energy events that cannot be accommodated by the flux anticipated by extrapolation of the present atmospheric neutrino measurements. Keywords Neutrinos · Cosmic rays · Astrophysics
1 The First Kilometer-Scale Neutrino Detector: IceCube A series of first-generation experiments [1, 2] have demonstrated that high-energy neutrinos with 10-GeV energy and above can be detected by observing Cherenkov radiation from secondary particles produced in neutrino interactions inside large volumes of highly transparent ice or water instrumented with a lattice of photomultiplier tubes. Construction of the first second-generation detector IceCube at the geographic South Pole was completed in December 2010 [3] (see Fig. 1). F. Halzen () Wisconsin IceCube Particle Astrophysics Center and Department of Physics, University of Wisconsin, Madison, WI 53706, USA e-mail: [email protected]
IceCube consists of 80 strings, each instrumented with 60 photomultipliers that are 10 in. in diameter and spaced 17 m apart over a total length of 1 km. The deepest modules are located at a depth of 2.45 km so that the instrument is shielded from the large background of cosmic rays at the surface by approximately 1.5 km of ice. Strings are arranged at apexes of equilateral triangles that are 125 m on a side. The instrumented detector volume is a cubic kilometer of dark, highly transparent and sterile Antarctic ice. Radioactive background is dominated by the instrumentation deployed into this natural ice. Each digital optical module (DOM) consists of a glass sphere containing the photomultiplier and the electronics board that digitizes the signals locally using an onboard computer. The digitized signals are given a global time stamp with residuals accurate to less than 3 ns and are subsequently transmitted to the surface. Processors at the surface continuously collect the time-stamped signals from the optical modules, each of which functions independently. The digital messages are sent to a string processor and a global event builder. They are subsequently sorted into the Cherenkov patterns emitted by secondary muon tracks, or electron and tau showers, which reveal the direction of the parent
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