Today's Journal Club is about a new addition to the Standard Model of fundamental particles.

Journal Club – Neutrino Vision

Article Updated: 24 Dec , 2015

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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?

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HeadAroundU
Guest
HeadAroundU
February 5, 2012 2:35 AM

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. grin

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

Torbjorn Larsson OM
Member
Torbjorn Larsson OM
February 5, 2012 5:33 PM

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

Anonymous
Guest
Anonymous
February 6, 2012 5:13 PM

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.

Torbjorn Larsson OM
Member
Torbjorn Larsson OM
February 6, 2012 9:08 PM

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.

Guest
Guest
Guest
February 7, 2012 12:12 AM

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.”

Peter
Member
Peter
February 5, 2012 2:03 PM

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.

Lawrence B. Crowell
Member
Lawrence B. Crowell
February 5, 2012 7:13 PM

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.

LC

Brian Howard
Guest
February 5, 2012 3:35 PM

I hope we achieve what we are hoping for.

Anonymous
Guest
Anonymous
February 5, 2012 5:34 PM

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.

Lawrence B. Crowell
Member
Lawrence B. Crowell
February 5, 2012 7:09 PM

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.

LC

Torbjorn Larsson OM
Member
Torbjorn Larsson OM
February 5, 2012 5:41 PM
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… Read more »
Zephyr
Member
February 8, 2012 3:40 AM
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… Read more »
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