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Energy Levels Influence Cosmic Ray Arrivals

NSF Award:

Analysis of IceCube Data at UW-Madison 2010-2013  (University of Wisconsin-Madison)

Cosmic-ray Physics with IceCube  (University of Delaware)

IceCube Maintenance and Operations 2010-2015  (University of Wisconsin-Madison)

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Researchers at the South Pole's IceCube Neutrino Observatory have detected directional variations of cosmic rays on multiple angular scales in the southern sky. These findings demonstrate that the same large-scale directional changes observed at energies around 20 teraelectron volts are not present at 400 teraelectron volts. This discovery departs from theoretical predictions.

Among the particles the IceCube detector can sense are muons--fundamental particles found in cosmic radiation. To trigger the IceCube detector some 2000 meters below the polar ice sheet, muons must possess energy of at least several hundred gigaelectron volts. Particles with that much energy are generated by primary cosmic rays with energies in excess of several tens of teraelectron volts. At these energies, theory predicts that interactions of cosmic rays with galactic magnetic fields should completely randomize the muons' arrival directions. However, the IceCube data suggests energy levels may influence the muons' arrival direction.   

An array of 5160 digital optical modules (DOMs) embedded in the ice record the high-energy particles as they pass through the IceCube detector. The DOMs are attached to 86 vertical cables--or strings--deployed at depths between 1450 and 2450 meters below the surface of the ice. Between 2009 and 2010, 59 strings were deployed and the detector ran in this smaller configuration. This research drew on 32 billion muon events recorded between May 2009 and May 2010.

Images (1 of )

  • intensity map for cosmic rays from a 20-teraelectronvolt sample
  • intensity map for cosmic rays from a 400-teraelectronvolt sample
Intensity map for a 20-teraelectronvolt sample.
IceCube Collaboration
Intensity map for a 400-teraelectronvolt sample.
IceCube Collaboration

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