Of Particular Significance

Ice Cube’s Neutrino Paper Appears

POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON 11/22/2013

Some readers may remember that back in May, as I discussed in some detail, the IceCube experiment reported a new and exciting observation — possibly the first discovery of high-energy astrophysical neutrinos: neutrinos, with energies 5 – 50 times higher than those of the protons at the Large Hadron Collider, created in outer space and arriving on earth.  This is to be contrasted with most neutrinos measured at IceCube and other previous similar experiments, which have lower energy and are created in the earth’s atmosphere by other types of particles hitting atoms in the air (see Figure 4 of this article.)   Specifically, where the IceCube folks expected to measure 10 candidate events from non-neutrino backgrounds, they instead measured 28.  Well, these results were reported at a conference in May, but only now is the paper appearing in published form, in the journal Science.

Here’s the IceCube press release about the publication of their paper, http://icecube.wisc.edu/news/view/171 .  All indications are that there are few changes since May, except for greater confidence in the result; the numbers quoted all match the ones that I wrote about back in the spring.  If there is anything strikingly different from May, I haven’t yet noticed it; please let me know if you’re aware of something.

For those of you who missed this back in May, I wrote a few relevant posts back then that you may find useful.

Meanwhile, you may also remember that there was a big Gamma Ray Burst [GRB] observed in April — the most energetic ever measured.  [We were hoping that IceCube would observe neutrinos from that GRB, but it did not.] Science is also publishing papers about that event, and how measurements of it are making people rethink their understanding of how GRBs occur.  Once I’ve learned more about this, I’ll post something more detailed.

Curiously, both of these stories are appearing in the press with big headlines, as though they are new news… but if they sound familiar, it’s because they are indeed six months old.

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16 Responses

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  2. Could dark matter be what is called strangelets or strange matter from possible quark stars? And, perhaps another silly question. If gravity is a particle than perhaps black holes could be concentrated gravitons or a graviton star?

    1. 1) I believe that this is not ruled out, though not considered likely — no one has ever confirmed that the strong nuclear force can make such things. I think also you’d have a very hard time explaining how these strangelets formed without messing up precision measurements of the early cosmos, from the cosmic microwave background radiation. But it requires calculation to check such things.

      2) Gravity isn’t a particle; gravitons are particles. The same idea applies to electric forces: electric forces are generated by electric fields, which are not particles; but *waves* in those fields are made from particles, called photons [the particles out of which light is made, hence the name].

      You can’t make a star from massless objects, such as gravitons or photons. They’ll simply escape from one another.

      However, you most certainly can make black holes from gravitons and photons. In fact you don’t need gravitons to be particles in order to do it; you can make black holes, even in Einstein’s non-quantum theory, out of gravitational (or electromagnetic) waves, without needing to use the fact that those waves are made from gravitons (or photons.)

  3. We are eager to read your comments about the models to understand how the fascinating GRBs occur. I would be particularly interested to know what do you think about the (“standard” for astrophysicists?) fireball models and the (“simpler” for some particle physicists?) cannonball model…

  4. Also, how does Ice Cube distinguish from a high energy neutrino signal and the signal of a much slower moving higher rest mass dark matter particle with the same momentum and a similar cross-section of interaction?

    1. I believe you could not make a consistent story (you’d need too many dark matter particles of too large a mass) but I don’t have time to confirm that right now.

      [You also wouldn’t get the muons they observe in some events, but of course those events could be background rather than signal, so I don’t want to make a claim based on that.]

  5. While super-high energy neutrinos are interesting, it seems like low energy ones would be more interesting. If you had a neutrino that was moving slowly enough (say 0.9c instead of 0.999c) and could accurately estimate its speed (e.g. with photons coming from a distant supernova for example and the low energy neutrinos coming at the tail end of the same event), you could directly measure its mass via the Lorentz transformation equations. Is there any experimental effort along those lines being done or would a low energy neutrino just require too sensitive a detector to pick up?

    1. Neutrino masses are at most 1 eV/c^2, so to see their slow speed you’d need to look for neutrinos with energy of a few eV or below. Such neutrinos interact much less often than MeV-scale neutrinos and are impossible to detect. You’re better off looking at the high-energy ones that travel for a very very long time, so you can tell the difference between .999999c and .99999c (don’t take these precise numbers seriously, I’m just making a point.)

      See http://neurotheory.columbia.edu/~larry/AbbottNP88.pdf for an old attempt to do this.

      Other methods for measuring neutrino masses (using cosmology) will work better, and certain direct measurements of rare atomic decays may work better. But this is a long story.

      As for high-energy neutrinos, they aren’t interesting in and of themselves, perhaps, but what they reveal may prove very interesting indeed. I don’t care about high-energy photons either, but the thing that makes the high-energy photons is another matter.

  6. I find it amazing that we can even make sense of such high energy events in context of standard model. What a huge range of validity.

    1. The range of validity of the Standard Model of particle physics is huge indeed, it could even go the Planck energy! (as far as I understand the so called “asymptotic safety” scenario for quantum gravity which made it possible to Shaposhnikov and coworkers to correctly predict the Higgs mass in http://arxiv.org/abs/0912.0208)

      1. Well, the “asymptotic safety” scenario isn’t obviously consistent. It’s more of a hope and a hand-wave than a real theoretical construct.

        Still, the Standard Model could be valid up to rather near the Planck scale.

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