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## Indication of Neutrino Transformation Observed128

AmiMoJo writes "A Japanese research group says it has observed for the first time an indication that a type of neutrino can change into another type. The group generated a large amount of neutrinos at the Japan Proton Accelerator Research Complex, or J-PARC, in the prefecture's Tokai Village, and aimed them at the Super-Kamiokande observatory in Gifu Prefecture about 300 kilometers away, to look for neutrino oscillation. As a result, the group observed that muon neutrinos can change into electron neutrinos."
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## Indication of Neutrino Transformation Observed

• #### proof (Score:4, Interesting)

on Friday June 17, 2011 @01:15AM (#36471356)
How do they know they were the same neutrinos they launched out?
• #### Re: (Score:3)

They don't measure single particles. That's not actually possible and doesn't quite make sense. They just take tons and tons of statistics.
• #### Re: (Score:2)

So, it just 'probably' happened?

• #### Re: (Score:3)

:)

Nah, they know the beginning ratio and ending ratio of the different types. If they are not the same, then some must have flipped (or rotated, or whatever language the neutrino guys use these days).
• #### Re: (Score:2, Informative)

Not necessarily. They could be different neutrinos, caused by atoms in the way absorbing some neutrinos and emitting others. I am not sure but I suspect that is what GP was getting at. Rather than evidence of neutrinos actually changing from one type to another, it seems just as likely (more likely?) that intervening matter performed a conversion. Just as, say, a crystal or a gas can "change" a laser's color by absorbing photons and then emitting others of a different frequency, maybe matter is absorbing th
• #### Re: (Score:2)

This would imply that the absorbing/emitting matter emitted it in exactly the same direction, which seems unlikely. Secondly, neutrinos are notorious for not interacting with matter. Thirdly, this process is believed to happen between sun and earth, which doesn't contain much matter.

• #### Re: (Score:2)

That's why I used the example of the laser: the photons are emitted in exactly the same direction, however unlikely you might think that is.
• #### Re:proof (Score:4, Insightful)

on Friday June 17, 2011 @07:14AM (#36472566)

Not necessarily. They could be different neutrinos, caused by atoms in the way absorbing some neutrinos and emitting others.

It's not entirely an oversimplification to say "that won't happen" - solar neutrinos pass straight through the Earth for example. (See the Wikipedia page [wikipedia.org])

• #### Re: (Score:2)

Do they? Or do they often collide with atoms and experience the same kind of "conversion"? As far as I know, nobody has performed any experiments to find out. The very idea that they might change from one form to another is very recent.
• #### Re: (Score:2)

Do they? Or do they often collide with atoms and experience the same kind of "conversion"? As far as I know, nobody has performed any experiments to find out. The very idea that they might change from one form to another is very recent.

On the contrary, we've been doing experiments about this non-stop for decades, and the answer is "no, neutrinos don't interact very much". While the interaction cross sections with things have kind of large error bars by particle physics standards, they're still known to ~20

• #### Re: (Score:2)

My fault... I should have been more specific. I am learning that lesson, having to deal with someone else who took an off-hand comment of mine and tried to turn it into a diatribe about how arrogant and ignorant I am.

I wasn't pretending to be rigorous here. I simply meant that we haven't performed this particular kind of experiment before, and even this one has only a relatively thin statistical line to call "evidence". Obviously we know that neutrinos don't interact much, or those huge underground detec

• #### Re: (Score:2)

I'm really sorry, but... you are ignorant, quite literally. You've ignored what people have written to you about neutrino flavor mixing. You're willfully ignorant, I'm afraid, and that certainly makes you appear arrogant.

Your theory (if I'm able to understand) is that this effect is due to coherent flavor-exchanging forward neutrino scattering. Others have replied, myself included, with some degree of clarity as to why this is not the case. The "why" of neutrino oscillation is because their mass eigenst

• #### Re: (Score:2)

I made an off-hand comment that maybe it was possible. People have since explained that it was not. My only argument here has been with people who have misunderstood my comments and have replied with arrogant, snide remarks about what they think I understand, and in some cases, about things I did not even write or ask.

I don't have a "theory". And my original comment had nothing to do with coherent scattering... I only mentioned the possibility that coherent scattering might exist, in a completely differe
• #### Re: (Score:2)

To clarify somewhat: I do not deny making the comment, nor do I deny that I did not properly word it in such a way as to indicate its semi- tongue-in-cheek nature. And I did get -- from the very beginning -- that it wasn't the correct answer. But I did allow some to think I hadn't, simply because of the unnecessarily odious nature of their responses.

As should be apparent from my comments above, I was aware that it wasn't likely a very realistic picture.
• #### Re: (Score:2)

Do they? Or do they often collide with atoms and experience the same kind of "conversion"? As far as I know, nobody has performed any experiments to find out.

A skeptic would see the bold part as the first and easiest problem to solve.

The very idea that they might change from one form to another is very recent.

I guess just over half a century is 'very recent' by some standards, but I'd say probably not by the standard of "recent enough for me to assume no experiments have been conducted."

• #### Re: (Score:2)

Maybe it is time for you to stop being such an asshole.

This was the first experiment of this kind to be performed, as you well know. Those others you mention over that last century are not relevant to my comment. Tell me: when was the last other experiment performed to find this evidence about the third leg of the oscillation?

What's that you say? Never? Wow. How about that.

I have no need to sit here and constantly be put down by somebody who obviously isn't even paying attention to what he's readin
• #### Re: (Score:2)

I think it'd be Nobel prize material if one found neutrino-stimulated neutrino emission, as that is what you're alleging. I'm not saying it's impossible, just that IIRC my undergrad physics at all, it'd be a big discovery.

• #### Re: (Score:2)

Bigger than, say, neutrinos spontaneously, and without obvious cause, changing from one form to another? I don't see why. In fact, I think it is the more likely explanation. It fits Occam's razor a hell of a lot better, because you don't have to assume some kind of spontaneous process from a cause unknown.
• #### Re: (Score:2)

Methinks (if there's a particle physicist here, may she/he chime in) that it'd be a brand new thing if either process was observed, just that apparently momentum preserving neutrino emission is way more exotic than changing of the flavor. The latter requires a "detail" in the Standard Model to be wrong (neutrinos can't be massless as assumed until now), the former is some truly brand new physics. Perhaps even the latter would be Nobel material. Seems like they adjusted the prize to the curve recently, wink

• #### Re: (Score:3)

I personally don't understand why parent is modded "Informative."

The process you propose is neutrino scattering: Muon neutrino interacts with an electron to produce an electron neutrino and a muon which decays, perhaps after being captured by a nucleus. This is a well known electroweak interaction with a rather well determined cross-section. The cross-section, or probability of interaction, is *extremely* small. Therefore, even though kinematic/scattering considerations (mentioned by another poster in th

• #### Re: (Score:2)

"Such mechanisms, having been well demonstrated and measured, are well understood. Oscillation of neutrino flavor, due to the neutrinos possessing (small) rest masses, is the effect which is observed and measured in this experiment."

You are saying that the cause of this oscillation is known? If so, can you enlighten us, or at least link to an explanation of this behavior? Because everything I have read about it so far says that (a) this is the first time it has been observed, and (b) the cause is unknown.

• #### Re: (Score:2)

Apologies in advance, but some knowledge of particle physics is required. Just as it's hard to describe a breakthrough in computer technology to someone who has little understanding of computers....

These two links (given further down in responses to this article) are much better technical explanations than I could write:

http://bit.ly/NuBlogT2KNuE1 [bit.ly]

(a) I believe this is the first direct observation. Previous experiments

• #### Skepticism. (Score:2)

Not necessarily. They could be different neutrinos, caused by atoms in the way absorbing some neutrinos and emitting others. I am not sure but I suspect that is what GP was getting at. Rather than evidence of neutrinos actually changing from one type to another, it seems just as likely (more likely?) that intervening matter performed a conversion.

So here's the thing about skepticism.

You start out with an excellent question -- how do we know (or rather, quantify our confidence that) it was the neutrinos changing in-flight, rather than something else, like them being absorbed and re-emitted by intervening matter?

Then, rather than treat this like a question to which you do not know the answer, and try to find out, you instead decide that it's "just as likely (more likely?)" that your interpretation is correct.

Skepticism is based around the idea of aski

• #### Re: (Score:2)

"Then, rather than treat this like a question to which you do not know the answer, and try to find out, you instead decide that it's "just as likely (more likely?)" that your interpretation is correct."

Don't be an ass. My opinion, so far, is that it seems just as likely. I did not claim or pretend that it was anything more than that. Further, if you actually used your brain, you would know that the probability that I, personally, had the equipment to perform such an experiment is just about nil. So your criticism is 100% hot air.

Don't lecture me about skepticism. I am all about looking for the answer... but there has, as yet, been no opportunity to do so! So you are talking out your ass. You ask the im

• #### Re: (Score:2)

Don't be an ass. My opinion, so far, is that it seems just as likely. I did not claim or pretend that it was anything more than that. Further, if you actually used your brain, you would know that the probability that I, personally, had the equipment to perform such an experiment is just about nil. So your criticism is 100% hot air.

So using your brain means concluding that there's no way to learn anything more, and so not trying?

I'd have thought using your brain meant realizing that what you're proposing means a neutrino interacting twice -- the first muon neutrino interacting with some matter, and the electron neutrino hypothetically emitted by that interaction itself interacting with the detector. Even setting aside the issue that the second neutrino would have to be emitted in the same direction, that means the probability of this

• #### Re: (Score:2)

I thought of the same objection as the OP, although I would have expressed it differently: the basis for the experiment is that massless neutrinos can't change type because they travel at the speed of light hence experience no proper time. But actually they only travel at the speed of light in a vacuum. Granted the proper time between emission and detection would still be awfully awfully small, but do we know for sure how quickly oscillation occurs (in proper time)?

I'd have thought using your brain meant realizing that what you're proposing means a neutrino interacting twice -- the first muon neutrino interacting with some matter, and the electron neutrino hypothetically emitted by that interaction itself interacting with the detector. Even setting aside the issue that the second neutrino would have to be emitted in the same direction, that means the probability of this occurring is the probability of a single interaction squared. It means your idea is highly dependent on the probability of neutrino-atom interactions.

I'm not sure that there's any problem wi

• #### Re: (Score:2)

I thought of the same objection as the OP, although I would have expressed it differently: the basis for the experiment is that massless neutrinos can't change type because they travel at the speed of light hence experience no proper time. But actually they only travel at the speed of light in a vacuum. Granted the proper time between emission and detection would still be awfully awfully small, but do we know for sure how quickly oscillation occurs (in proper time)?

Photons only travel at less than the speed of light in a non-vacuum because of interactions; between interactions (between atoms, which is a vacuum) they still travel at the speed of light. It's the only speed a photon can travel at. It's not like the properties of light implied by masslessness and speed-of-light travel cease to be in a medium. :)

So I would strongly suspect that the QM-implied oscillations still require mass-full neutrinos, even taking into account mediums through which they travel. If th

• #### Re: (Score:2)

Photons only travel at less than the speed of light in a non-vacuum because of interactions; between interactions (between atoms, which is a vacuum) they still travel at the speed of light.

I strongly suspect that the effect is the same. The interactions aren't actually discrete because both the atoms and the photon are subject to quantum mechanics. Also remember that the atoms are fairly closely packed. (In the case of neutrinos, though, I guess the only interaction is with the quarks, which *aren't* closely packed, so that may be another problem with my suggestion!)

The photon-through-glass thing requires many, many interactions so the average is what we see when we treat the light as if they were rays bent by glass-air interfaces.

I don't think that's true - the critical fact is that the interaction might have been with any of the atoms. Even a single p

• #### Re: (Score:2)

I strongly suspect that the effect is the same. The interactions aren't actually discrete because both the atoms and the photon are subject to quantum mechanics.

The theoretical implications aren't, though. I mean, photons don't act like mass-full particles in a non-vacuum, and things traveling as fast as light through a given medium doesn't make the thing behave as if mass-less like a photon.

It's true I was cheating, treating the interactions as classical discrete events. But in a QM sense, the probability of seeing a photon is based on the interference of all possible paths, and that interference is based on the phase, which is based on the path length, the wave

• #### Re: (Score:2)

[...] I mean, photons don't act like mass-full particles in a non-vacuum [...]

No, I suppose not. I probably hadn't thought about it hard enough - there's an effective Hamiltonian which is different from the real one, but I guess it just looks like a change in the distance scale, not like a mass term. A change in the refractive index can act like a gravitational field (my thesis was about figuring out how much Hawking radiation you should see in materials with a rapidly changing refractive index) but I presume moving through a gravitational field doesn't cause generation mixing, oth

• #### Re: (Score:2)

Which brings up another question: do you know whether the measured rate of neutrino mixing gives us a lower bound for the neutrino mass? Or is it a strictly binary zero/nonzero thing?

It tells us the difference between their masses, so it is a lower limit on mass-having neutrinos -- the lower limit for any neutrino could still be 0! Google tells me this difference is 0.07 +- 0.04 eV. And other observations have only yielded upper limits, of around 20 eV.

Afraid not. But my gut tells me it shouldn't. Consider a hypothetical very thin pane of glass, so that the typical photon only interacts once; or, better still, consider the ideal model of a mirror. Each photon only interacts once when bouncing off a perfect mirror, but because the single interaction is with all the atoms simultaneously (i.e., a superposition) it still bounces off at the expected angle.

I'm having trouble mentally mapping this to the situation in question. It seems like it's saying the neutrinos should be reflected back at the emitter, instead of reaching the distant detector. :/

• #### Re: (Score:2)

And here's another thing about skepticism:

The skeptic looks for potential causes for an observation, rather than accepting that it happens spontaneously or through "mysterious" processes. If the cause is unknown, then speculation as to the possible cause is not only called for, but necessary. Further evidence will not be forthcoming until those speculations are tested.

I do not claim to be as qualified to speculate on the matter as professional physicists; nevertheless, in an absence of explanation I s
• #### Re: (Score:2)

The skeptic looks for potential causes for an observation, rather than accepting that it happens spontaneously or through "mysterious" processes. If the cause is unknown, then speculation as to the possible cause is not only called for, but necessary. Further evidence will not be forthcoming until those speculations are tested.

And then they think about that potential explanation, and what it implies, and whether it can explain the evidence, and if it does if there's any aspect of the evidence that can distinguish between this and other hypothesis.

And of course the actual scientists have been doing this for some time, and this experiment will hopefully further the cause. But look at you with your "rather than accepting that it happens spontaneously or through 'mysterious' processes". Implying that others are doing this, while yo

• #### Re: (Score:2)

"You can't just blow off that kind of arrogance-ignorance cocktail by saying 'It's just my opinion.'"

Sure I can. You tell me: what is the most likely hypothesis for why this happens? Not how... stop getting that confused. I asked why. What is the cause behind neutrino oscillation?

I will patiently wait for at least one, or hopefully at least three hypotheses about the cause of these theoretical oscillations. I don't want to hear any garbage about waveforms and probability. That's a how. I asked for a why. Which you STILL seem to be having a hard time understanding. There is a difference, you know.

So..

• #### Re: (Score:2)

[L]acking any other offer of an actual cause, my opinion is as good as any other.

To get back to the source of this argument, from several days ago: The cause is neutrino flavor oscillation. Your opinion holds no weight.

Why didn't you reply to my last post in this thread, which was addressed to you? Why scream at someone else instead of reading my stuff and asking questions? You come off as someone who isn't gifted with a mind to understand particle physics, and who is really pissed off at the world and especially at people who do understand particle physics because others do and you

• #### Re: (Score:2)

If you look at the nature of this person's responses to me, from the very beginning, you will have your answer. No matter the content of the conversation, I have no reason to be nice to insufferable assholes.

The fact is that I know a hell of a lot more about this than I let on. But I wanted to give this person room to have his say.

• #### Re:proof (Score:5, Informative)

on Friday June 17, 2011 @01:32AM (#36471458)

Yes. This is how statistics works.

The standard definition of "probably" in the particle physics community is a five-sigma signal, which means that the odds of it happening by chance are 1.4 * 10^-14.

• #### Re: (Score:2)

Yes. This is how statistics works.

The standard definition of "probably" in the particle physics community is a five-sigma signal, which means that the odds of it happening by chance are 1.4 * 10^-14.

No. The probability of a five-sigma signal (from a Gaussian) is exactly 0. The probability of a five-sigma sigma signal or one more extreme is 5.7 * 10^-7. I don't know where you got your number, but it isn't right.

• #### Re: (Score:2)

Given that:
a. a mole of substance contains somewhere around 10^23 particles
b. 300 km between the source and the detector. Not to mention that the source is "Ibaraki Prefecture, east of Tokyo" (TFA), not exactly too far away from Fukushima
c. "neutrino beams" are hardly something actually possible
d. lots of other sources for neutrinos

odds of 10^-14 magnitude doesn't seem actually that low. But maybe I'm wrong.

• #### Re: (Score:2)

a. What does a mole have to do with anything? You don't have a mole of neutrinos.
b. Neutrinos don't tend to care what gets in their way, and move really fricken' fast. I doubt 300 km matters much.
c. Neutrino beams are possible and do exist.
d. Yes, there are lots of sources, but those sources can be measured and controlled for.

• #### Re: (Score:1)

a. What does a mole have to do with anything? You don't have a mole of neutrinos.
b. Neutrinos don't tend to care what gets in their way, and move really fricken' fast. I doubt 300 km matters much.

How many possible sources of "noise" you have in 300 km? (i.e. radioactive particles that just decided to emit a neutrino?)

c. Neutrino beams are possible and do exist.

[quotation needed] I can't imagine how you manage to make sure your neutrino emissions goes only in a predetermined direction (thus, actually build a beam from them), I'd be happy to be shown how.

d. Yes, there are lots of sources, but those sources can be measured and controlled for.

Hmmm... are they now? Can you control all the radioactive decays that lead to a neutrino somewhere in those 300 km? (this assuming you can tell the direction of an incoming neutrino that intera

• #### Re:proof (Score:5, Informative)

on Friday June 17, 2011 @03:40AM (#36471958)

How many possible sources of "noise" you have in 300 km? (i.e. radioactive particles that just decided to emit a neutrino?)

The odds that a random bit of radioactive material creates a neutrino that just so happens to hit your detector are very small. And they can be controlled for...

Can you control all the radioactive decays that lead to a neutrino somewhere in those 300 km?

I get the feeling you're not well versed in science. You don't "control" every radioactive decay. You control for them. You run a control experiment and figure out how many and what sorts of neutrinos you expect to see. Then you turn on your neutrino source, and see how the counts change.

And here's a source for the existence of neutrino beams: http://en.wikipedia.org/wiki/Magnetic_horn [wikipedia.org]

• #### Re: (Score:2)

I get the feeling you're not well versed in science... You control for them.

Or, as an alternative explanation, I might have missed the for word in what you said.

• #### Re: (Score:2)

The odds that a random bit of radioactive material creates a neutrino that just so happens to hit your detector are very small.

You might have missed the following bit from grand-parent:

Not to mention that the source is "Ibaraki Prefecture, east of Tokyo" (TFA), not exactly too far away from Fukushima

• #### Re:proof (Score:5, Informative)

on Friday June 17, 2011 @04:19AM (#36472096)

I can't imagine how you manage to make sure your neutrino emissions goes only in a predetermined direction (thus, actually build a beam from them), I'd be happy to be shown how.

Relativity, essentially. The neutrinos head off in random directions in the rest frame of the emitter. You take a beam of high energy muons, and keep them in a storage 'ring', with two or three long straight sections precisely aligned at the detector.* If your muons start with high energies compared to the energy of their decay, you will get a fairly well collimated beam of neutrinos.

*Or at least it used to be, in the case of J-PARC. It's going to take them a while to sort the mess out.

• #### Re: (Score:2)

not exactly too far away from Fukushima

Makes me wonder if the recent earthquakes put their aim off, possibly requiring recalibration at the sending end. I know this happens to radars after large quakes.

• #### Re: (Score:1)

not exactly too far away from Fukushima

Makes me wonder if the recent earthquakes put their aim off, possibly requiring recalibration at the sending end. I know this happens to radars after large quakes.

Pre-print here. [jnusrv01.kek.jp] They used data from the first two runs (Jan-Jun 2010 and Nov 2010-Mar 2011). I can guess why Run 2 ended when it did. The speculation about earthquakes and Fukushima contamination are unfounded.

• #### Re: (Score:2)

Makes me wonder if the recent earthquakes put their aim off, possibly requiring recalibration at the sending end. I know this happens to radars after large quakes.

In fact, the quake shut down the neutrino beam, it will remain off till next year as they carefully line it up again.

This paper is from the data they got before the quake shut things down.

• #### Re: (Score:2)

Why not? You filter out other kinds of decay with a block of lead, and run the signal from the single muon through a PMT [wikipedia.org], and presto, you have a measurable signal.

This is a standard undergraduate modern physics lab experiment.
• #### How can they detect anything at all? (Score:1)

I thought neutrinos almost never interact with more regular matter because they're too small to collide with atoms, how can they get their statistics?

• #### Re: (Score:2)

You said it, _almost never_. The neutrinos coming from JPARK are all emitted as muon type neutrinos. What they are looking for at Super-K are electron type neutrinos. Neutrino oscillations will convert some of the muon neutrinos to electron neutrinos and a very small fraction of these will be seen at Super-K. Based on the number of neutrinos seen, even if it is small, they can estimate the number that oscillated. In this case, they saw 6 events.
• #### Re: (Score:2)

This still begs the question: they are claiming that this is a "new type" of neutrino oscillations. So what causes the oscillations? So far I have yet to see an explanation, anywhere.
• #### Re: (Score:2)

It is empirical science. They do not have to have a reason for it. They just have to rule out reasons that they could be due to faulty machinery. And that it does not fit current models. After that it becomes a question of "how an this be explained"

• #### Re: (Score:2)

I am aware of that. But my question was, and is still: what causes it? Not how does it happen, but why. I don't think that question was vague or ambiguous, but people keep giving me HOWs when I asked about WHY. Just as you have pointed out.

I understand that we may not yet have an answer, that was part of my point earlier on. But a lot of people (some of them with quite a snooty, superior air, present company excepted) keep answering a question I did not even ask, then have insulted me for not knowing the
• #### Re: (Score:2)

So far I have yet to see an explanation

Have you thought of looking? [lmgtfy.com]

• #### Re: (Score:2)

Yes, in fact I have. There is lots of information about neutrino oscillation. But the particular information that I was asking about, that is, the cause of neutrino oscillations (which you would know if you had actually been paying attention rather than being a snotty smartass), is not, to the best of my knowledge, to be found there.

Lots of information about how they oscillate. Or possibly how... that hasn't been proven yet either. A good source of information about that is Paradoxes of Neutrino Oscilla [trieste.it]
• #### Answer, the Second. (Score:2)

But the particular information that I was asking about, that is, the cause of neutrino oscillations (which you would know if you had actually been paying attention rather than being a snotty smartass), is not, to the best of my knowledge, to be found there.

I paid attention, it's why I googled you up "why" for you. Did you pay attention? The answer to your question was right in there! You may have had to click a link in the text to get to the fuller explanation, sorry! But the answer I already gave you is: It's a natural consequence of neutrinos having (different) masses, and quantum mechanics. In QM, the neutrino isn't a classical particle of one well-defined type sailing along, that "mysteriously" decides to become a different particle in the middle.

• #### Re: (Score:3)

Almost never isn't never. I can't speak for all neutrino detectors, but a friend of mine works in a lab where they use tanks of scintillator, studded with PMTs, and lined with tons of shielding to keep out everything else. Every now and then a lucky neutrino bumps into a scintillator molecule, and creates a little flash. The PMTs amplify the fuck out of it, and by carefully analyzing the resulting data you can pick out specific types of neutrinos from the noise.

• #### Re: (Score:2)

I thought neutrinos almost never interact with more regular matter because they're too small to collide with atoms, how can they get their statistics?

About 60 billion solar neutrinos pass through every square centimeter of the Earths surface every second, give or take.

The Super-Kamiokande has a cross section of about 630000 cm^2 (~20 m diameter), so roughly 3.2 * 10^18 solar neutrinos pass through the detector each day.

When looking for solar neutrinos, the Super-Kamiokande had about 15 events per day which they could attribute to solar neutrinos...

• #### Re: (Score:2)

Stamped the back of their hands then checked that they had the stamp before letting them back in?
• #### Re: (Score:2)

My guess is they selected only neutrinos coming from that particular direction.

• #### Re: (Score:2)

No, we know of no way to block neutrinos comming from any direction. They probably counted the neutrinos they would naturaly gather, then turned their source on and counted again what neutrinos they detected.

• #### Re:proof (Score:5, Informative)

<dido' at' imperium.ph'> on Friday June 17, 2011 @02:06AM (#36471600)

They don't, not in every case at least. They do, however, know the magnitude of the output neutrino flux from the accelerator in J-PARC, and from the process that generated them, that they are supposed to be muon neutrinos. The Super-Kamiokande is designed to detect neutrinos, as well as determine the type of neutrino they are detecting, and given the magnitude of the flux directed to them from J-PARC, they have statistical models that allow them to determine the statistical increase in the number of neutrino detection events they ought to see. Presumably they detected just about the number of neutrinos that they were supposed to, except that they weren't all muon neutrinos, as they would have expected if neutrinos did not oscillate, but a certain fraction of the increase were identified as electron neutrinos.

The phenomenon of neutrino oscillations [wikimedia.org] has been suspected for a long time, ever since the number of neutrinos coming from the sun was observed to be significantly less than expected, given the known models of the sun's nuclear reactions (which generate lots of neutrinos). This was before methods for detecting other neutrino types than the electron neutrino were developed, and the solar neutrino problem [wikimedia.org] was a major open problem in physics for a long time. The same Super-Kamiokande was instrumental in establishing that the phenomenon of neutrino oscillation was the solution to the solar neutrino problem.

This experiment is similar, but potentially it can be more finely controlled (not dependent on the far less controllable neutrino flux from the sun), so by fine-tuning it they can determine experimentally more properties of these mysterious particles. The phenomenon of neutrino oscillations is physics that lies beyond the Standard Model, and as such is bound to be extremely interesting. I do hope that J-PARC can continue their experiments soon, as their operations were affected by the Great Touhoku Earthquake last March.

• #### Re: (Score:2, Informative)

by Anonymous Coward

Note: I'm a neutrino physicist AC.

Neutrino oscillations are real, and have been proven a long time ago (MINOS even saw the energy dependence!). What's new here is that one of the oscillation parameters (theta_13) was assumed to be zero. The probability of a muon neutrino oscillating to an electron neutrino is directly proportional to sin theta_13; so, if the angle is zero, the probability is zero, and muon neutrinos cannot become electron neutrinos. The fact that SK saw muon neutrinos becoming electron neut

• #### Re: (Score:1)

Wish I could mod you +1 informative for being the most actually informative comment in this thread and the only one that explains the actual physical significance.
• #### Re: (Score:2)

"Note: I'm a neutrino physicist AC.

Neutrino oscillations are real, and have been proven a long time ago (MINOS even saw the energy dependence!) ..."

Who modded this comment down? It was the most informative yet to appear in this thread.

I am curious about a couple of things:

(1) What is the proposed mechanism by which these neutrinos oscillate? If flavor is a measurable property, then how can they "spontaneously" change?

(2) Correct me if I am wrong, but if, as you suggest, theta_13 is not zero, then (a) we have another example of parity violation, and (b) one more piece of evidence that the "Standard Model" is wrong.

Which means -- again if I

• #### Re: (Score:1)

by Anonymous Coward

Physics student here. What follows in my understanding of the situation, so I can make no guarantees that it is completely accurate.

As for the mechanism, well, it comes down to neutrinos having mass eigenstates which are different from flavor eigenstates, and statistics. I believe this is something of a simplification, but when a neutrino is created in a reaction, it produces one with a flavor eigenstate specific to the reaction. Conservation of mass-energy then locks the neutrino into a mass eigenstate, b

• #### Re: (Score:2)

Yeah! If it happened at the same time as my evening dump, I could have been making a ton of electron neutrinos at the time! Especially if I had cheese that night!
• #### Groundbreaking! Unprecedented! (Score:5, Informative)

on Friday June 17, 2011 @01:19AM (#36471370)

observed for the first time an indication that a type of neutrino can change into another type

Oh, really? [wikipedia.org]

• #### Re:Groundbreaking! Unprecedented! (Score:4, Informative)

on Friday June 17, 2011 @01:48AM (#36471512)

It's a particular oscillation that they've observed for the first time.

Assuming this result is correct then this result implies that there is a CP symmetry violation between the neutrino and anti-neutrino.

Previously to this result this particular mixing term could have been zero and if it was zero then CP symmetry would have been preserved.

Tim.

• #### Re: (Score:1)

Could you say that again, but with more words this time?
• #### Re: (Score:3)

I can try. But as someone else has replied what I wrote is not actually correct.

Because there are three different neutrinos, we need three different numbers to describe how they can oscillate (change) between flavours.

What oscillate means is that if you start with a beam of pure electron neutrinos and then, at some later time measure the type of the neutrinos you will find that some of them are now muon or tau neutrinos.

Two of those numbers were known to be non-zero. This result suggests that the third numb

• #### Re: (Score:3, Informative)

by Anonymous Coward
Hmm, don't think so. This mixing can be nonzero (i.e. what they observed) and the CP violating phase could still be zero, in fact the T2K analysis assumes \delta_{CP} = 0 as there is currently no information on the CP violating phase. T2K's article [jnusrv01.kek.jp]
• #### Re: (Score:2)

Yes, you're right. I had thought that non-zero theta13 was sufficient.

• #### Corrections (Score:5, Informative)

on Friday June 17, 2011 @06:12AM (#36472404) Journal
Sorry but your post is not informative it is just plain wrong: I think you are confusing the US-based MINOS and MiniBooNE experiments with the Japanese-based T2K experiment which the article is talking about.

It's a particular oscillation that they've observed for the first time.

No it is not. SuperK first observed this type back in 1998 but the results were not conclusive (they saw muon neutrino "disappearing" but not what they converted into). Since then MINOS and MiniBooNE have observed this exact type of neutrino oscillation (around 2003 IIRC - but they have multiple papers published now) and the OPERA experiment has even got some evidence of muon to tau oscillation. (Look them all up in Wikipedia or Google).

Assuming this result is correct then this result implies that there is a CP symmetry violation

No it does not. For T2K (the experiment they are talking about) to see a matter/antimatter asymmetry (CP violation) one of the mixing angles, theta_13 must be large and they need a LOT more data.

• #### Re: (Score:2)

Assuming this result is correct then this result implies that there is a CP symmetry violation between the neutrino and anti-neutrino.

The oscillation T2K just observed is not related to CP violation. It's simpler than that. There are three types of neutrinos. If they can change types, then there are three ways they could do so (draw yourself a triangle with each neutrino at a vertex, the sides are how they could change into each other).

Solar neutrinos start of as electron neutrinos and change on their wa

• #### Tiny lil' bastards! (Score:3)

on Friday June 17, 2011 @01:25AM (#36471406) Homepage
Getting those little tags on em is a bitch!
• #### Re:Tiny lil' bastards! (Score:4, Funny)

on Friday June 17, 2011 @01:28AM (#36471424)
I pity whoever has to catch them, then put those rings around their little legs
• #### Re: (Score:3)

Seriously, you should. A friend of mine does this. She spends weeks at a time at the bottom of an abandoned mineshaft, with a swimming pool full of scintillator, working 14 hour days, and earns doctoral candidate pay, which is to say, slightly less than your average FedEx driver.

• #### Re: (Score:2)

Seriously, you should. A friend of mine does this. She spends weeks at a time at the bottom of an abandoned mineshaft, with a swimming pool full of scintillator, working 14 hour days, and earns doctoral candidate pay, which is to say, slightly less than your average FedEx driver.

And, to wax poetic, in return, she gets to see the ripples from god's fingers in the aether. I envy the people who work with her level of dedication on experiments like these.

• #### OH GOD (Score:1)

THE NEUTRINOS HAVE MUTATED
• #### Re: (Score:2)

THE NEUTRINOS HAVE MUTATED

Get me a SyFy channel commissioning editor, and some washed up actress who people might remember from that one thing in 1994, and who's still sort of MILFish from some angles, if you're into older chubby chicks, stat

• #### Re: (Score:2)

Gaah! [zazzle.com] No! No! No! [dudeitsnot...eworld.com]

by Anonymous Coward on Friday June 17, 2011 @07:16AM (#36472572)

I am a physicist working on the experiment, for more information on this story please check out my blog post http://bit.ly/NuBlogT2KNuE1

• #### Re: (Score:2)

Or look here. [science20.com]

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