Journal Club – Neutrino Vision


According to Wikipedia, a journal club is a group of individuals who meet regularly to critically evaluate recent articles in the scientific literature. And of course, the first rule of Journal Club is… don’t talk about Journal Club.

So, without further ado – today’s journal article is about the latest findings in neutrino astronomy.

Today’s article:
Gaisser Astrophysical neutrino results..

This paper presents some recent observations from the IceCube neutrino telescope at the South Pole – which acually observes neutrinos from the northern sky – using the Earth to filter out some of the background noise. Cool huh?

Firstly, a quick recap of neutrino physics. Neutrinos are sub-atomic particles of the lepton variety and are essentially neutrally charged versions of the other leptons – electrons, muons and taus – which all have a negative charge. So, we say that neutrinos come in three flavours – electron neutrinos, muon neutrinos and tau neutrinos.

Neutrinos were initially proposed by Pauli (a proposal later refined by Fermi) to explain how energy could be transported away from a system undergoing beta decay. When solar fusion began to be understood in the 1930s – the role of neutrinos was problematic since only a third or more of the neutrinos that were predicted to be produced by fusion were being detected – an issue which became known as the solar neutrino problem in the 1960’s.

The solar neutrino problem was only resolved in the late 1990s when the three neutrino flavours idea gained wide acceptance and each were finally detected in 2001 – confirming that solar neutrinos in transit actually oscillate between the three flavours (electron, muon and tau) – which means that if your detector is set up to detect only one flavour you will detect only about one third of all the neutrinos coming from the Sun.

Ten years later, the Ice Cube the neutrino observatory is using our improved understanding of neutrinos to try and detect high energy neutrinos of extragalactic origin. The first challenge is to distinguish atmospheric neutrinos (produced in abundance as cosmic rays strike the atmosphere) from astrophysical neutrinos.

Using what we have learnt from solving the solar neutrino problem, we can be confident that any neutrinos from distant sources have had time to oscillate – and hence should arrive at Earth in approximately equal ratios. Atmospheric neutrinos produced from close sources (also known as ‘prompt’ neutrinos) don’t have time to oscillate before being detected.

When looking for point sources of high energy astrophysical neutrinos, IceCube is most sensitive to muon neutrinos – which are detected when the neutrino weakly interacts with an ice molecule – emitting a muon. A high energy muon will then generate Cherenkov radiation – which is what IceCube actually detects. Unfortunately muon neutrinos are also the most common source of cosmic ray induced atmospheric neutrinos, but we are steadily getting better at determining what energy levels represent astrophysical rather than atmospheric neutrinos.

So, it’s still early days with this technology – with much of the effort going in to learning how to observe, rather than just observing. But maybe one day we will be observing the cosmic neutrino background – and hence the first second of the Big Bang. One day…

So… comments? Are neutrinos the fundamentally weirdest fundamental particle out there? Could IceCube be used to test the faster-than-light neutrino hypothesis? Want to suggest an article for the next edition of Journal Club?

29 Replies to “Journal Club – Neutrino Vision”

  1. Quarks must be weirdest, one of them is called strange. :d

    It could test a supernova right? But, I don’t believe they are faster. Religion for the win. 😀

    We need article about AMS, but they don’t have data yet I guess. I checked their site some time ago…

    1. Supernova neutrinos have been used to extract neutrino speed. It is slightly lower than photon speed over the same (vacuum) distance.

      1. It’s true that the neutrinos arrived here slightly behind the photons, in the case in point. The consensus view is that the neutrino speed was, however, indistinguishable from that of light. The slight delay is attributed to the physical development in the supernova itself. Neutrinos leave the source after the initial photons do.

      2. There is no such consensus view, presumably the consensus view would be as I described because neutrinos are relativistic massed particles. This we know since the observed neutrino oscillations are predicted by such.

        You missed the point of the experiment, maybe because I didn’t make it explicit: they can limit the speed to relativistic speed.

      3. I’m not going to argue the point, but it has been argued in a number of papers that the 1987A neutrino speeds are consistent with lightspeed. These arguments are currently being repeated ad nauseum to counter recent claims for superluminal speeds. Perhaps “ad nauseum” would have been a better word choice than “consensus.”

  2. When you say “extragalactic origin”, do you actually mean, neutrinos from outside our own galaxy? I would think that would be several orders of difficulty more than just distinguishing between atmospheric and other origins.

    1. The neutrino type which acts as a trigger for an extragalactic source are tau neutrinos. These are not produced in appreciable number in the atmosphere.


    2. Yes from outside our galaxy – likely sources are gamma ray bursts or active galactic nuclei. Extragalactic neutrinos are thought to be the upper enegy level range of neutrinos received (so that is how you would distinguish them).

  3. Neutrinos originating in the Sun are electron neutrinos. At lower energies, they should not oscillate appreciably, at least according to theory that has been used to explain the apparent solar deficiency. So their numbers should not be reduced in transit. In recent measurements, however, these lower energy neutrinos are indeed too few, and by the same factor of two or three that oscillation (presumably) has reduced those of higher energy.

    This vitally important observation would seem to caste doubt on the accepted explanation. Why is this not discussed openly? There is perhaps insight here into the sociology of science.

    1. The relativistic energy E of a particle with mass m and momentum p is

      E = sqrt{p^2 + m^2} = p sqrt{1 + (m/p)^2} ~= p + m^2/2p

      where c = 1 and the last approximation is the binomial series for p >> m, the extreme relativistic limit. The unitary evolution of the particle is

      |?(t)> = e^{-iEt/?}|?(0)> =~ e^{-ipt/?}e^{-im^2t/p?}|?(0)>

      The first of these is a phase term we can ignore. The mass is a matrix which has different masses for different neutrino types, called the PMNS matrix. The dependency on the energy is p ~= E and as such the generator m^2/p? of the phase becomes small. The periodicity of the oscillations then increases.


    2. Well, you are discussing it openly. You say ‘There is perhaps insight here into the sociology of science’. Why?

      Comments like ‘Why is this not discussed openly’ imply conspiracy.

      The oscillation theory is well entrenched in consensus. It makes sense and there is evidence to back it up. But history has shown again and again that someone who can overturn consensus with a lot of hard work and evidence could potentially win a Nobel prize. There is huge motivation to pursue that outcome.

      1. “Conservation of Theory” and “Conservation of Face” are most likely at play here. There is much more to science than science, unfortunately. Egos and careers are dominating features.

      2. Well, sure it’s a human endeavour.

        No-one ever lost a science job being controversial. Making stuff up is how you wreck a science career.

      3. The neutrino mass matrix and oscillations is pretty much standard particles physics. It is a late 1970 to early 1980 particle physics development, and has been well established by experimental data. The neutrino mass matrix predicts mass differences between neutrinos, however it does not predict the absolute masses of each. The absolute masses are not well known.

        There are people who have lost careers for being controversial, and even right in the end. However, doing things like faking data is a sure fire way of getting booted out.


      4. This is what conspiracy theorists forget. You don’t make a career in any scientific field by playing “follow the leader”. You make a career by savagely destroying as much of the work that came before you as you possibly can:). Of course, most people fail to do that, because the people that came before them were just as smart as they are.

      5. History tells a different story. An example:

        Aristarchus of Samos proposed, published, his correct view of the solar system around 300-400 BC. It was ignored and forgotten. Copernicus revived it again about 2000 years later. He did so timidly, and one might say “prudently,” from his death bed.

      6. However, the scientific community today is very different from the Scholastic environment of the late medieval period. There does not exist the sort of ecclesiastical authority over science; of course that might change in the US here before long. In the ancient world there were not the tools to really test the systems of Arstarchus and Ptolemy, and Ptolemy’s system fit within the Aristotlean system better. These were different time periods with different modes of thinking very different from today’s.


      7. Same prople doing the same things, just different rationales. Read some of Rupert Sheldrake’s discussion of this issue.

        Glad to hear at least someone thinks we have finally overcome human nature, though.

      8. That was way before modern science with global publication and peer review existed.

        Thanks for testing the hypothesis that you are implying conspiracy theory (by your description of something else entirely)!

      9. “Conspiracy.” Buzzword freak, eh?

        Same prople doing the same things, just different rationales. Read some of Rupert Sheldrake’s discussion of this issue. At any rate, I’m out of here.

      10. Now you have to go to anti-science blogs to continue your commentary, since that _is_ a conspiracy theory, and directed against well established and well merited climate science.

        Actually it would be much more difficult to cheat in climate science due to the political and public open oversight (through IPCC). You have to go to other socially, but not scientifically, controversial areas like stem cell research to find similar degrees of oversight.

        If it was scientifically controversial no public oversight would be needed, because very few scientists would work with it. See cold fusion.

  4. Could IceCube be used to test the faster-than-light neutrino hypothesis?

    Confusing, since as UT has reported this is exactly what has been done a while ago. The result is that a ftl neutrinos hypothesis have to be rejected:

    “IceCube has detected neutrinos with energy 10,000 times higher than any generated as part of the OPERA experiment, leading Cowsik to conclude that their parent pions must have correspondingly high energy levels. His team’s calculations based on laws of the conservation of energy and momentum revealed that the lifetimes of those pions should be too long for them to decay into superluminal neutrinos.

    As Cowsik explains, IceCube’s detection of high-energy neutrinos is indicative that pions do decay according to standard ideas of physics, but the neutrinos will only approach the speed of light; they will never exceed it.”

    Some other hypothesis is needed to explain the OPERA observations. The leading suspect remains systematic errors.

    Meanwhile repeats of OPERA experiments by independent observatories are considered, but I can’t remember whether any will use IceCube.

  5. Where is that particle detector that assigns unique sounds to detected particles? Somewhere in Europe. I think study at all the different wavelengths falls down because there is little integration of data. You may capture a unique particle, but not the source, nor its trajectory. If we point all our telescopes at a black hole, we know we are looking at a net source of gravity emission, a negative of a photon, not necessarily an anti-photon, but what are we going to detect? a lack of light? I still like the tachyon, faster than light backward through time, neutrinos sit there for me, in between cronons and gravitons, far more interesting as far as particles go. I feel Cronons and gravitons make sense in the same way as gluon’s, holding things together, and sit somewhat awkwardly next to membranes in string theory. I see the the universe as infinite and eternal, too big for maths, maybe I need to be burnt at the stake like Giordano Bruno. Where are we situated in the big bang, in the centre? to the left of right of the centre? I think we should be surveying around the most distant quasars with multi wavelength simultaneous observations over longer durations, like Chandra and Hubble ultra deep field observations. My guess is if there are Quasars that far away, they took a while to form from hypergiants to quasar and then the light travelled and reached us. If you capture a group of neutrinos you need to know where they came from, what was lost in the atmosphere then there are questions like what were they before, how have they decayed. I don’t like them, parsing through everything, it just not right. 🙂

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