Monday, June 24, 2013

1306.5021 (Luis A. Anchordoqui et al.)

Pinning down the cosmic ray source mechanism with new IceCube data    [PDF]

Luis A. Anchordoqui, Haim Goldberg, Morgan H. Lynch, Angela V. Olinto, Thomas C. Paul, Thomas J. Weiler
Quite recently the IceCube Collaboration has reported an observation of 26 neutrino candidates above ~ 50 TeV. Including the two ~ 1 PeV neutrinos reported earlier in 2013, these 28 events constitute a 4.3\sigma excess compared to the atmospheric background. In this article, we investigate the compatibility between the data and an unbroken power-law neutrino spectrum, for various values of spectral index \Gamma >= 2. We show that \Gamma ~ 2.3 is consistent at the ~ 1.5\sigma level with the observed events up to 1 PeV and to the null observation of events at higher energies. We then assume that the sources of this unbroken spectrum are Galactic, and deduce (i) an energy-transfer fraction from parent protons to pions (finding \epsilon_\pi), and (ii) a discriminating test between the two most popular models ("dip" and "ankle") for the Galactic to extragalactic cosmic-ray transition. Future IceCube data will test the unbroken power law hypothesis, and, if the neutrino sources are Galactic, discriminate between the "dip" and "ankle" models of Galactic to extragalactic transition.
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