An article in Science, Evidence for High-Energy Extraterrestrial Neutrinos at the IceCube Detector, claims to have detected 28 neutrinos from an unidentified extra-solar location that has yet to be identified. From what I can gather, the only evidence for determining the origin of a neutrino is based only on the energy of said neutrino. Based on the large energy content of those observed, the hypothesis is that the neutrinos are from outside the solar system, making them the first extra-solar neutrinos ever detected.

How accurate is using energy to identify the neutrinos? Presumably it is statistically possible, although perhaps very unlikely, that the energies observed were created inside the solar system. Is there a probability density function describing expected energy values for atmospheric and intra-solar-system generated neutrinos? Where do the newly observed neutrinos fit into those probabilities?

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    $\begingroup$ arXiv version was posted today too: arxiv.org/abs/1311.5238 Also, these would be the second extrasolar neutrinos, the first being from SN 1987A. $\endgroup$ – user10851 Nov 22 '13 at 23:24

We know what the solar neutrino spectrum looks like from direct measurement (Super-K has even imaged the sun in neutrinos). Likewise we know what the spectrum of neutrinos coming from cosimc ray interactions in the atmosphere and the body of the early looks like. And the spectrum for our nuclear reactors and that from the uranium and thorium in the deep earth.

IceCube is looking for sources other than these well known spectra and at much higher energy than most of them go to (solar and reactor neutrinos have energies of MeV, most cosmic neutrinos run MeV or GeV the data set just published runs from 30--1200 TeV).

Little is understood about neutrino production at these energies, but they are assumed to be the decay products of very high energy pions and kaons created in energetic astrophysical events. There are some models, and IceCube uses one as a benchmark.

Also IceCube gets some (often limited1) directional information as well as energy. With a statistically size set of events you could rule in or out origin in the Milky Way (and particularly at the center) and perhaps some of the larger nearby galaxies as well.

1 I presume that the shower events have much coarser angular resolution than the muon quasi-elastic events which should give good pointing data at these high eneries. The big limit on the showering events is going to come because IceCube is very coarsely instrumented by comparison to the detector I have worked on (but of course it is also a gigaton detector so they can fully contain those 1000 TeV events!).

  • $\begingroup$ Note at this point I have only ready the first few pages of the paper...grading to do and all that. $\endgroup$ – dmckee Nov 23 '13 at 0:05

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