University of Wisconsin-Madison

Research Highlights: Cosmic Ray Physics

IceCube is a powerful neutrino telescope but also a huge muon detector that registers more than 100 billion muons per year, produced by the interaction of cosmic rays in the Earth’s atmosphere.

Once we measured the arrival directions of the atmospheric muons, an anisotropy at the level of 10-3 was revealed that shows significant structure on multiple angular scales. We have also observed structure on scales between 15 degrees and 30 degrees with even lower amplitudes. The origin of these anisotropies is still unknown.

Using IceTop, the IceCube air shower array sensitive to cosmic rays between 100 TeV and 1 EeV, we have extended measurements of the cosmic-ray anisotropy at the 10-3 level to PeV energies. We have shown that this anisotropy persists to PeV energies, although with phase reversal. No time-dependent variations are observed, in agreement with current theoretical models.

Relative intensity maps of the cosmic ray-anisotropy measured with 318 billion cosmic-ray-induced events detected in IceCube between May 2009 and May 2015 (in polar coordinates). The median energy of the data shown in each map is indicated in the upper left. Maps have been smoothed with a 20-degree smoothing radius.
Relative intensity maps of the cosmic ray-anisotropy measured with 318 billion cosmic-ray-induced events detected in IceCube between May 2009 and May 2015 (in polar coordinates). The median energy of the data shown in each map is indicated in the upper left. Maps have been smoothed with a 20-degree smoothing radius.

We have performed studies of the chemical composition of cosmic rays using the combined IceTop shower and IceCube muon data. We found a transition from light to heavier nuclei as energy increases, which may be associated with the end of the galactic cosmic-ray spectrum. We have also reported a measurement of the all-particle cosmic-ray energy spectrum in the energy range from 1.6 PeV to 1.3 EeV using data from IceTop, which exhibits clear deviations from power law behavior.

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Take a closer look at the highest energy neutrinos.