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In recent days, gentle readers, you may recall me mentioning within these pages that there were significant new results on the way from the Tokai-to-Kamioka long-baseline neutrino oscillation experiment (or T2K for short). After weeks of checking and validation[*], those results were released to the world today and can now be shared.
This morning, my boss was on the BBC Radio 4 programme Today to discuss the new announcement. Press releases can also be seen by clicking on one of the following links:
To summarize, there are three known types of neutrinos but, thanks to the wonders of quantum mechanics, they match up differently depending on how you look at them. In one way of looking, you get three distinct "flavours": the electron neutrino (which pairs with an electron), the muon neutrino (which pairs with the electron's heavier cousin, the muon), and the tau neutrino (which pairs with the beast of the lepton family, the tau). If you examine the neutrinos by mass, you also see three types -- or three distinct masses. So far, not terribly surprising, right? Well hold on, because here comes the good part:
The three mass states and the three flavour states do not correspond to each other. If you take a garden variety neutron and wait about fifteen minutes, it will decay into a proton, an electron, and an electron neutrino[**]. That electron neutrino has a definite flavour... but not a definite mass. Its mass is actually a mixture of the three mass states. Since objects of different mass with the same energy travel at different speeds -- consider, for instance, pitching a baseball versus a bowling ball -- the three mass states of that electron neutrino travel in a manner that is slightly different for each. When you later go to look at that neutrino again, the mixture may have changed enough to make that electron neutrino look like a muon neutrino. Or a tau neutrino. Wait a bit longer and look again, though, because it may well have changed back into an electron neutrino once more!
This is a process called "neutrino oscillation" and it is not a part of the Standard Model of Particle Physics! It was first discovered by my thesis experiment, Super-Kamiokande, in 1998, when they measured a lack of muon neutrinos (caused by some of them turning into the much more difficult to detect tau neutrinos). Since then, other experiments have replicated these results: The K2K and MINOS experiments have produced beams of muon neutrinos to confirm this disappearance, and both Super-Kamiokande and SNO have seen electron neutrinos from the Sun disappear as they turn into the two other types. Similarly, the KamLAND experiment noticed electron anti-neutrinos from nuclear reactors vanishing as they turned into the corresponding other types of anti-neutrinos.
Since there are three types of neutrinos (call them ν1, ν2, and ν3), there are three types of mixing possible: mixing between 1&2, mixing between 2&3, and mixing between 1&3.
The initial discovery by Super-Kamiokande in 1998, described above, is mixing between types 2&3. So is the mixing studied by K2K and MINOS. The Solar neutrino studies by Super-Kamiokande and SNO measured mixing between types 1&2. However, there has been no strong indication of mixing between types 1&3. Until now. This is the big news from T2K. Although we have only collected about ~3% of our expected total data[***], we already see compelling signs of this mixing! Exciting, no?
For those who may still be unimpressed, I should point out that measurements of the three types of mixing is an essential pre-requisite for measurements of another property of neutrinos, which is called "CP violation". The "C" stands for "charge conjugation", which is basically means flipping a particle to its anti-particle: An electron to a positron, a proton to an anti-proton, et cetera. The "P" stands for parity; if you look at your hands, you will see an example of a parity flip -- the two are the same except for a mirror image transformation. It was once believed that matter and anti-matter were the same if you flipped both "C" and "P". We now know that this is not quite true. That is a good thing, as were they the same in every way, equal amounts of matter and anti-matter would have been created in the Big Bang... then subsequently annihilated together and left nothing behind to make us! So CP symmetry is not exactly; however, the small amount by which this symmetry is violated amongst the fundamental particles known as quarks is not nearly sufficient to explain why we live in a universe that is filled with matter. Measuring the CP violation amongst neutrinos may give us the answer.
For those who are interested in learning more, feel free to download a pre-print of our publication, which was submitted to Physical Review Letters on Monday and will be available on the arXiv server tomorrow. There is no need to wait, as you can get a copy of the pre-print here.
Also, if any of you have any questions about this result, dear friends, do feel free to ask. I anticipate the next few days being particularly busy, but I will try to answer any questions as quickly as possible!
[*] Which was the reason that I postponed my trip to Seoul until next year.
[**] Technically, this case gives an electron anti-neutrino... but don't worry about that difference right now. For the sake of this explanation, the two can be treated as the same.
[***] And will be getting no more until about early next year, thanks to the East Japan Big Earthquake and Disaster.
This morning, my boss was on the BBC Radio 4 programme Today to discuss the new announcement. Press releases can also be seen by clicking on one of the following links:
- The UK's Science & Technology Facilities Council [STFC] (Click here)
- The Japan Proton Accelerator Research Complex [J-PARC] (Click here)
To summarize, there are three known types of neutrinos but, thanks to the wonders of quantum mechanics, they match up differently depending on how you look at them. In one way of looking, you get three distinct "flavours": the electron neutrino (which pairs with an electron), the muon neutrino (which pairs with the electron's heavier cousin, the muon), and the tau neutrino (which pairs with the beast of the lepton family, the tau). If you examine the neutrinos by mass, you also see three types -- or three distinct masses. So far, not terribly surprising, right? Well hold on, because here comes the good part:
The three mass states and the three flavour states do not correspond to each other. If you take a garden variety neutron and wait about fifteen minutes, it will decay into a proton, an electron, and an electron neutrino[**]. That electron neutrino has a definite flavour... but not a definite mass. Its mass is actually a mixture of the three mass states. Since objects of different mass with the same energy travel at different speeds -- consider, for instance, pitching a baseball versus a bowling ball -- the three mass states of that electron neutrino travel in a manner that is slightly different for each. When you later go to look at that neutrino again, the mixture may have changed enough to make that electron neutrino look like a muon neutrino. Or a tau neutrino. Wait a bit longer and look again, though, because it may well have changed back into an electron neutrino once more!
This is a process called "neutrino oscillation" and it is not a part of the Standard Model of Particle Physics! It was first discovered by my thesis experiment, Super-Kamiokande, in 1998, when they measured a lack of muon neutrinos (caused by some of them turning into the much more difficult to detect tau neutrinos). Since then, other experiments have replicated these results: The K2K and MINOS experiments have produced beams of muon neutrinos to confirm this disappearance, and both Super-Kamiokande and SNO have seen electron neutrinos from the Sun disappear as they turn into the two other types. Similarly, the KamLAND experiment noticed electron anti-neutrinos from nuclear reactors vanishing as they turned into the corresponding other types of anti-neutrinos.
Since there are three types of neutrinos (call them ν1, ν2, and ν3), there are three types of mixing possible: mixing between 1&2, mixing between 2&3, and mixing between 1&3.
The initial discovery by Super-Kamiokande in 1998, described above, is mixing between types 2&3. So is the mixing studied by K2K and MINOS. The Solar neutrino studies by Super-Kamiokande and SNO measured mixing between types 1&2. However, there has been no strong indication of mixing between types 1&3. Until now. This is the big news from T2K. Although we have only collected about ~3% of our expected total data[***], we already see compelling signs of this mixing! Exciting, no?
For those who may still be unimpressed, I should point out that measurements of the three types of mixing is an essential pre-requisite for measurements of another property of neutrinos, which is called "CP violation". The "C" stands for "charge conjugation", which is basically means flipping a particle to its anti-particle: An electron to a positron, a proton to an anti-proton, et cetera. The "P" stands for parity; if you look at your hands, you will see an example of a parity flip -- the two are the same except for a mirror image transformation. It was once believed that matter and anti-matter were the same if you flipped both "C" and "P". We now know that this is not quite true. That is a good thing, as were they the same in every way, equal amounts of matter and anti-matter would have been created in the Big Bang... then subsequently annihilated together and left nothing behind to make us! So CP symmetry is not exactly; however, the small amount by which this symmetry is violated amongst the fundamental particles known as quarks is not nearly sufficient to explain why we live in a universe that is filled with matter. Measuring the CP violation amongst neutrinos may give us the answer.
For those who are interested in learning more, feel free to download a pre-print of our publication, which was submitted to Physical Review Letters on Monday and will be available on the arXiv server tomorrow. There is no need to wait, as you can get a copy of the pre-print here.
Also, if any of you have any questions about this result, dear friends, do feel free to ask. I anticipate the next few days being particularly busy, but I will try to answer any questions as quickly as possible!
[*] Which was the reason that I postponed my trip to Seoul until next year.
[**] Technically, this case gives an electron anti-neutrino... but don't worry about that difference right now. For the sake of this explanation, the two can be treated as the same.
[***] And will be getting no more until about early next year, thanks to the East Japan Big Earthquake and Disaster.
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From:
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From:
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There are three flavour eigenstate and three mass eigenstates. The different types of eigenstates are related to each other by a U(3) unitary transformation known as the PMNS (Pontecorvo, Maki, Nakagawa, Sakata) matrix.
Thus, each flavour eigenstate is a superposition of the three mass eigenstates, and vice versa. Weak interactions, such as the example I gave above of a beta decay, produce neutrinos in their flavour eigenstates (e.g., an electron neutrino). However, they propagate via their mass eigenstates. Due to the difference in masses between these eigenstates, they propagate with wave functions of different wavelengths. This means that, when re-observed via a flavour interaction, those three wavelengths will be out of phase and, when recombined to a total flavour state, the new superposition of these out-of-phase wave functions may give you a different flavour than the one you started with.
That is a more accurate explanation, though more difficult to present to anyone who is not terribly familiar with the intricacies of quantum mechanics. Hopefully it clears things up for you? (If not, feel free to ask again!)
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(And you are quite welcome. I thought it would be much clearer when I moved to a more rigorous description -- one physicist to another!)
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If I fire a proton at a target (using, say, the device at T in T2K), I get a pion which decays into a muon and a muon anti-neutrino, which combined carry the momentum and energy of the pion.
If I were to ask you "where's the muon?" you'd be able to say "it's wave function says about *there*, plus or minus delta-x" where "there" is a location which is moving, and delta-x is probably increasing over time.
If I were to ask you "where's the neutrino?", would the wave function say "a superposition of here, here, and here", with one "here" for each mass eigenstate? Or does the neutrino, despite being a mixture of mass eigenstates, propagate with a single position (well, as single a position as Heisenberg will allow, anyway)? Or is it "here, here, and here, but the three here's are so close that uncertainty prevents them from being distinguished"?
Or am I barking up the wrong tree?
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It's a good question. The second answer is the better one. There is still one neutrino, but the mass eigenstates have different frequencies in their wave function. It isn't really that one is moving more slowly than another; it's more like waves getting out of phase and then being recombined. Sometimes the pattern of waves makes it look like an electron neutrino when viewed in flavour-space; other times the pattern makes it look like a muon (or tau) neutrino.
Does that make sense?
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If so, nice joke. If not... well, give it a think and if you come up with another question -- or just find that you are less sure than you thought -- feel free to ask!
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My understanding of the answer is that when a pion decays into a muon and a neutrino, it is in state |m> when looking at the flavor eigenstates, but the flavor eigenstates aren't eigenstates of the Hamiltonian (the "time passes operator", if I understand it). The mass eigenstates are. The |m> state is |1+2+3> (for some weights on the three mass states), so after it propagates it's still in state |1+2+3>, but now in a different mix of |e+m+t>, a mix which varies with time. When a flavor state is observed, it picks a flavor eigenstate as per standard wave function collapse rules.
Is that about right?
What I don't understand is what it means to propagate through space in state |1+2+3>. Which is what I was trying to ask, but not sure I got an answer to.
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So in non scientist & in effect lasyman's terms. what does your discovery mean? what practical non theoretical 9implications does it have?
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Knowing that
We are going out shortly for a celebratory drink at the pub. I will try to write more on the Oxford Tube later so that I can answer your other questions.
Hope all is well with you and you are having a good day!
From:
no subject
Also makes me feel like I'm in an episode of the Big Bang Theory.
:O)
From: (Anonymous)
Excited isn't the word
Love & hugs
dahne
From:
Re: Excited isn't the word
I am now trying to line up professional speaking engagements to lecture on the big news. Will definitely be looking forward to a more laid-back chat in October at the usual place!
Love & Hugs & Bright Blessings,
N
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This might explain why I'm a historian, not a scientist! :o)
I have longered pondered on what a quantum mechanic keeps in their toolbox................
As Sir Pterry says- I am not sure what this means, but it's probably quantum.
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On the physics front I'm much more at home with discussions of how much of an early modern battle would have been visible through the black powder smoke and the hitting power of various arrow head forms when coming into contact with armour.
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Well, if you are interested in learning more, I would be happy to chat with you at some point. I pride myself on being rather practiced at communicating physics and astronomy results and would wager that by the time we were done, you would understand it suitably well.
If, on the other hand, tis not your cup of tea... well, that's okay, too!
Just let me know and I will be more than happy to continue the conversation, possibly in person!
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Congratulations on being part of this!
*tight hugs*
I love you
xxxxxx
xxxxxx
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Also, am very glad that you followed me explanation! Huzzah!
Hope you are having a good evening... and that tonight's party goes amazingly well!
Love you LOTS!!!
xxxxxx
xxxxxx
xxxxxx
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So the neutrinos created by the event are in a super-positional state, not only of location/speed as is often the case but also of mass and spin? Meaning they are all 3 flavours at once? And it's only when you measure that they collapse into a particular flavour? If so, are they now fixed as that flavour of neutrino? Or if left alone will they oscillate again?
Finally, I actually read about researches into into Neutrino oscillations about a year ago and that article explained the basis of the observed oscillations, and then said it meant that neutrinos experienced time. And when I asked my other physicist friend he said 'I work on atmospheric physics! Leave me alone!' but guessed that it meant for a state change to occur then there must be time for it to happen in. But if my understanding outlined above is right this oscillation is actually just a collapsing quantum waveform, thus no time is needed for it to happen.
Or am I missing the point entirely?
PS please forgive misused terms - I may be using them wrong. Often when I try to get specific with a physicist I just further confuse things by misapplying terms or concepts from one area to another where they don't apply
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I thought I understood what you wrote (at least the words seemed to make sense) but then on thinking about it couldnt really see the significance or application of it all. Probably dont really have enough science to understand the concepts involved past the actual words themselves (and my how things/knowledge has changed in the past 50 years or so since I did science at school!!)
But it's still interesting. Will probabl get you to explain it a bit more when I next see you.
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Congratulations!
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(Takes me a while!!!) More interesting than I first thought especially as I have always wondered in a vague and non scientific sort of way why matter and ant-matter dont cancel themselves out.
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What does this mean in terms of employment for you? ;-)
(I'm sure you can guess why I'd be in that sort of headspace).
Also, were you guys still wanting to stop by ours on your way to/from other destinations? If so, what dates would we be talking about?
xx