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Indication of Neutrino Transformation Observed

timothy posted more than 3 years ago | from the you-become-the-particle-you-want-to-be dept.

128

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."

cancel ×

proof (3, Interesting)

Dr Max (1696200) | more than 3 years ago | (#36471356)

How do they know they were the same neutrinos they launched out?

Re:proof (2)

global_diffusion (540737) | more than 3 years ago | (#36471380)

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:proof (2)

davester666 (731373) | more than 3 years ago | (#36471412)

So, it just 'probably' happened?

Re:proof (2)

global_diffusion (540737) | more than 3 years ago | (#36471436)

:)

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:proof (1, Informative)

Jane Q. Public (1010737) | more than 3 years ago | (#36472074)

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 these neutrinos and emitting others with different properties.

Re:proof (2)

AlecC (512609) | more than 3 years ago | (#36472306)

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:proof (1)

Jane Q. Public (1010737) | more than 3 years ago | (#36476384)

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 (0)

Anonymous Coward | more than 3 years ago | (#36472336)

How the f*ck does an atom absorb a neutrino?

Neutrino absorption (2)

OeLeWaPpErKe (412765) | more than 3 years ago | (#36472522)

Well, since it isn't subject to magnetic or electrical forces, it basically has to slam into the nucleus (extremely unbelievably unlikely) or into an electron (unbelievably massively completely entirely extremely ... well about the same chance that anyone in the world likes a justin bieber song).

Essentially, it needs to get close enough to another particle - by coincidence - for the weak force to start having a decent effect on them.

Re:Neutrino absorption (1)

Jane Q. Public (1010737) | more than 3 years ago | (#36476648)

You are saying, in effect, that radioactivity is unlikely.

And statistically, it is, I suppose.

All I am doing is speculating. So far, I have not seen anybody (aside from a commenter here who so far has given no evidence) that there is a cause known for this "oscillation". I am simply guessing -- no more than that -- at a possible cause, rather than assume it is somehow spontaneous.

Re:proof (3, Insightful)

Tim C (15259) | more than 3 years ago | (#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:proof (1)

Jane Q. Public (1010737) | more than 3 years ago | (#36476414)

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:proof (1)

habig (12787) | more than 3 years ago | (#36478666)

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%, and are Really Tiny. A good perspective - the mean free path for your typical neutrino is something like a light year of lead before it interacts with matter at all, and when it does, it's not doing flavor changing. How do we know? Since we can't build a light year of lead sized experiment to catch half of the neutrinos we shoot, we build them as big as we can and shoot trillions of neutrinos per accelerator pulse, run the thing every couple seconds for years at a time, and observe those few neutrinos which are so incredibly unlucky as to smack something dead-on. How dead on? The weak force has a range of ~10^-18m. A proton is only 10^-15m in size. So a neutrino happily passes straight through a proton most of the time, to say nothing of all the empty space in an atom (which are 10^-10m in size).

On the other hand, the data fit the hypothesis of quantum mechanical flavor mixing quite well. That happens regardless of the presence of matter. However, if there is a lot of matter in the way (say, solar neutrinos exiting the core of the sun) it is a big effect - the "MSW Effect" explains how the presence of matter nearby changes neutrino oscillations.

In the case of the earth (which has a comparatively puny mount of matter) the effects are a lot more subtle, but neutrino beams going through a lot of the earth should be sensitive to this in the next decade or so. The Japanese beam is comparatively short so isn't ideal for such a measurement, the under-construction NOvA experiment in the US will do better, and people would really like to do a Fermilab->South Dakota beam to nail it down in spades.

Re:proof (1)

Chris Burke (6130) | more than 3 years ago | (#36478976)

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:proof (1)

tibit (1762298) | more than 3 years ago | (#36472994)

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:proof (1)

Jane Q. Public (1010737) | more than 3 years ago | (#36476464)

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:proof (2)

siglercm (6059) | more than 3 years ago | (#36474392)

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 this thread) are ignored, your proposed mechanism cannot account for the observed changes in neutrinos. I'm fairly certain analysis of this data takes your proposed mechanism into account as a background. Its effect, of course, is negligible.

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.

Re:proof (1)

Jane Q. Public (1010737) | more than 3 years ago | (#36476514)

"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.

Skepticism. (1)

Chris Burke (6130) | more than 3 years ago | (#36476286)

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 asking honest questions, and then looking for the answer.

Skepticism is not based around asking a rhetorical question (or just phrasing it as a statement), not bothering to find an answer, and assuming that your ability to ask a question means the conclusions of the research are now in doubt.

I hope this help clears up a common confusion regarding question asking and skepticism.

Re:Skepticism. (1)

Jane Q. Public (1010737) | more than 3 years ago | (#36476606)

"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 impossible of me, and berate me for not delivering it.

I did not try to present ignorance as evidence. I was clearly speculating, and as you well know, at this time any real evidence is still waiting to show up. And I will be happy to accept that evidence, if it was responsibly gathered. Until then, I am entitled to my opinion as to what is more likely.

Re:Skepticism. (1)

Chris Burke (6130) | more than 3 years ago | (#36478580)

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 occurring is the probability of a single interaction squared. It means your idea is highly dependent on the probability of neutrino-atom interactions.

And then you could have used your brain to deduce that people have already performed experiments indicating the odds of neutrino interaction, so you don't have to.

But I guess, "Well I can't conduct particle physics experiments myself, so I'll just run with what I already know" counts as using your brain... to justify ignorance.

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 impossible of me, and berate me for not delivering it.

There's nothing impossible about googling "Neutrino", learning more about them, and figuring out if your hypothesis is remotely likely or not.

But by saying it was impossible for you to learn more, and using that as your excuse for arriving at a premature opinion, you exemplify what I'm talking about even as you deny it.

I did not try to present ignorance as evidence. I was clearly speculating, and as you well know, at this time any real evidence is still waiting to show up. And I will be happy to accept that evidence, if it was responsibly gathered. Until then, I am entitled to my opinion as to what is more likely.

You're always entitled to your opinion; there's no "until". Whether you are exercising proper skepticism in arriving at it is a different matter. For example, there is ample evidence that applies to your hypothesis. You surely must have known there at least could be, yet did nothing to seek it out, and didn't even ask "Hey, does anyone know if this scenario seems plausible?" Nope, in a cloud of ignorance, you arrived at the opinion that these scientists ignored an obvious explanation that was at least, or more, likely than what they claimed.

And now you're defending that opinion on the basis that your ignorance was impossible to fix. You are implicitly saying that "I don't know" is a basis for arriving at a conclusion.

So, don't be an ass, you say? It is my policy to be an ass to asses whose first thought on a subject they don't understand is "Hey I spent 3 seconds thinking and 0 seconds investigating my idea, and I think it's just as likely -- maybe more likely! -- that I'm right and these people who do understand the subject are idiots!"

Next time be a real skeptic, which means being skeptical of your own ideas first. Instead of forming a conclusion, ask sincere questions. "Is this possible?" instead of "I think they're probably wrong!"

Re:Skepticism. (1)

Jane Q. Public (1010737) | more than 3 years ago | (#36476998)

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 still have a right to speculate.

Re:Skepticism. (1)

Chris Burke (6130) | more than 3 years ago | (#36478800)

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 you're the one furthering science by looking for causes.

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

I do not claim to be as qualified to speculate on the matter as professional physicists; nevertheless, in an absence of explanation I still have a right to speculate.

And yet you did claim that you were at least as likely, if not more likely, to be right and the professional physicists wrong. Please don't explain how this is just your opinion. Of course it is. The point is -- in your opinion, you're qualified to opine that they are probably wrong, and in fact that you're going to believe so until you are proven wrong. In your opinion, they aren't considering obvious explanations.

So, your words ring hollow. If you really believed that, you would have formed the opinion that the physicists probably know what they're doing, and your idea, even if you think it has merit, is the long-shot.

Yes it's just your opinion, just speculation. If you understood skepticism, then the opinion you formed would have reflected that understanding. Get it?

Re:proof (5, Informative)

Entropius (188861) | more than 3 years ago | (#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:proof (1)

Ardeaem (625311) | more than 3 years ago | (#36471746)

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:proof (0)

Anonymous Coward | more than 3 years ago | (#36472970)

Is that one-tailed or two-tailed? :)

Re:proof (1)

ekgringo (693136) | more than 3 years ago | (#36473808)

African or European?

Re:proof (1)

c0lo (1497653) | more than 3 years ago | (#36471748)

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:proof (1)

artor3 (1344997) | more than 3 years ago | (#36471846)

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:proof (0)

c0lo (1497653) | more than 3 years ago | (#36471888)

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 interacted in your detector).

Re:proof (5, Informative)

artor3 (1344997) | more than 3 years ago | (#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:proof (1)

c0lo (1497653) | more than 3 years ago | (#36471988)

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:proof (1)

ArsenneLupin (766289) | more than 3 years ago | (#36472548)

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 (4, Informative)

Shimbo (100005) | more than 3 years ago | (#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:proof (0)

Anonymous Coward | more than 3 years ago | (#36473720)

Hmm I see... like some kind of Pythagoras for speed. But then by playing with the speed of the muons, and finding out the sweet spot where the thin end of the triangle barely falls in the detector, they can deduce the speed of the neutrinos in the rest frame of the emitter. Then with another experiment, they can measure the energy of the neutrinos in the rest frame of the emitter. This would give them the neutrino mass.

Re:proof (1)

MichaelSmith (789609) | more than 3 years ago | (#36472794)

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:proof (1)

cstepan (731228) | more than 3 years ago | (#36473424)

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:proof (1)

habig (12787) | more than 3 years ago | (#36474732)

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.

We demand Six Sigma! (0)

Anonymous Coward | more than 3 years ago | (#36471994)

Wait, what are we talking about again?

Re:We demand Six Sigma! (-1)

Anonymous Coward | more than 3 years ago | (#36472090)

Niggers, beaners, chinks, nips, gooks, dune coons, wogs, krauts, limeys, rednecks, greaseballs, polacks, paddys, kikes, russkis, pilferers and froggies.

Re:proof (0)

Anonymous Coward | more than 3 years ago | (#36471638)

And you 'probably' didn't take high-school chemistry or physics?

Re:proof (0)

Anonymous Coward | more than 3 years ago | (#36471470)

Hmm measuring single neutrinos is actually possible. See for example the exact number of neutrinos observed by 3 different observatories [wikipedia.org] during a supernova.

I think it's fine to not know this, but you went out of your way to reply to someone with disinformation, why? That doesn't quite make sense.

Re:proof (0)

Anonymous Coward | more than 3 years ago | (#36471662)

But the question was about measuring the same neutrino more than once - how else would you detect oscillation on a single neutrino?

Re:proof (2, Informative)

Anonymous Coward | more than 3 years ago | (#36471772)

They don't need to measure the type of neutrinos they're emitting, they already know what type they are.

Re:proof (1)

habig (12787) | more than 3 years ago | (#36474802)

They don't need to measure the type of neutrinos they're emitting, they already know what type they are.

But if you measure what the neutrino beam looks like right after you make it (by sampling a tiny fraction of the neutrinos), then you get an even better measurement.

And T2K does - they have a whole suite of "near detectors" to carefully characterize what got made, and so can do a great "before and after" experiment.

Re:proof (1)

Chris Burke (6130) | more than 3 years ago | (#36475902)

Reposting the excellent blog entry posted by an AC far below claiming to be the author of said blog (and no reason not to believe 'em):

And yeah, it says there's a set of detectors 280m away, and the final set 295km.

Of course this still means that they aren't measuring "the same" neutrinos like in the original question, but that's just not feasible.

Re:proof (3, Insightful)

Artifakt (700173) | more than 3 years ago | (#36471740)

Only a very small fraction of neutrinos are captured by any detector. Most pass through without interaction. It's not possible to produce a neutrino, and swear that you have actually captured that particular neutrino at another spot. What the Japanese did is ran a procedure that created only (or at least predominately) a particular type of neutrino, and looked to see if the neutrinos arriving at the detector were all the same type (or types). Since the detector was also capturing the normal amount of neutrinos from other sources, such as the sun, in the normal mix of types, all that could be determined was that the total percentages of various types was either going to match all the other natural sources plus a spike in the one type emitted, or it wasn't, in which case some of the neutrinos from the source were changing phase.

Anonymous Coward, again putting the A and C into character assassination.

Re:proof (1)

tm2b (42473) | more than 3 years ago | (#36471580)

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.

Re:proof (0)

Anonymous Coward | more than 3 years ago | (#36471602)

...They're neutrinos. Not muons. The odds of an emitted neutrino even physically reacting with the detector is pretty slim.

Re:proof (1)

tm2b (42473) | more than 3 years ago | (#36471684)

Whoops, obviously a brain fart on my part. Oy. But they *do* measure individual neutrino interactions via the Cherenkov radiation emitted from their interactions in very large reservoirs of shielded heavy water.

Re:proof (1)

habig (12787) | more than 3 years ago | (#36474682)

But they *do* measure individual neutrino interactions via the Cherenkov radiation emitted from their interactions in very large reservoirs of shielded heavy water.

Just regular water in this case. Very pure water (well over 100m attenuation length for light in that water), and a lot of it (50,000 m^3), but still just ordinary water.

Re:proof (0)

Anonymous Coward | more than 3 years ago | (#36474046)

Yes, single particle detection can work for particles that interact strongly with their surroundings. Now, neutrinos on the other hand...

Re:proof (0)

Anonymous Coward | more than 3 years ago | (#36471632)

This is exactly what they do!! They're results are based on the observation of 6 electron neutrinos. The actual submitted article to Physical Review Letters, http://jnusrv01.kek.jp/public/t2k/node/2 [jnusrv01.kek.jp]

How can they detect anything at all? (1)

satuon (1822492) | more than 3 years ago | (#36471812)

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:How can they detect anything at all? (2)

evanoc (1056288) | more than 3 years ago | (#36471868)

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:How can they detect anything at all? (1)

Jane Q. Public (1010737) | more than 3 years ago | (#36477420)

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:How can they detect anything at all? (1)

matfud (464184) | more than 3 years ago | (#36479324)

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:How can they detect anything at all? (2)

artor3 (1344997) | more than 3 years ago | (#36471894)

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:How can they detect anything at all? (1)

Lord Crc (151920) | more than 3 years ago | (#36473228)

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:proof (0)

Anonymous Coward | more than 3 years ago | (#36471418)

They checked their name-tags.

Re:proof (2)

Billlagr (931034) | more than 3 years ago | (#36471448)

Stamped the back of their hands then checked that they had the stamp before letting them back in?

Re:proof (1)

toQDuj (806112) | more than 3 years ago | (#36471554)

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

Re:proof (1)

marcosdumay (620877) | more than 3 years ago | (#36476860)

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 (4, Informative)

dido (9125) | more than 3 years ago | (#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:proof (2, Informative)

Anonymous Coward | more than 3 years ago | (#36472628)

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 neutrinos mean that theta_13 cannot be zero.

If theta_13 isn't zero, it means that a more bizarre effect can happen with neutrinos. Theoretically, it's possible that neutrinos and antineutrinos oscillate in a different way; this difference is captured in another parameter, delta. But if you work out the calculations, delta always appears multiplying sin theta_13, or, if theta_13 was zero, delta would never make a difference and neutrinos and antineutrinos would always have the same oscillation. Since theta_13 isn't zero, we can now look for this difference, which is an important way to differentiate between various theories.

Re:proof (1)

wdsci (1204512) | more than 3 years ago | (#36477564)

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:proof (1)

Jane Q. Public (1010737) | more than 3 years ago | (#36477612)

"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 am not mistaken -- there have been at least 4 or 5 experiments in just the last year saying the same thing: that our Standard Model is off in various ways. And even more evidence if we go back 2 years.

Re:proof (1)

Greyfox (87712) | more than 3 years ago | (#36473850)

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!

tsunami (1)

cheeks5965 (1682996) | more than 3 years ago | (#36471364)

what's the connection with fukashima?

Re:tsunami (1)

c0lo (1497653) | more than 3 years ago | (#36471756)

what's the connection with fukashima?

Some good source of "rogue neutrinos", I guess.

Groundbreaking! Unprecedented! (4, Informative)

pushing-robot (1037830) | more than 3 years ago | (#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! (3, Informative)

locofungus (179280) | more than 3 years ago | (#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:Groundbreaking! Unprecedented! (0)

FrootLoops (1817694) | more than 3 years ago | (#36471698)

Could you say that again, but with more words this time?

Re:Groundbreaking! Unprecedented! (2)

locofungus (179280) | more than 3 years ago | (#36472052)

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 number is also non-zero.

I had thought that all three numbers being non-zero was sufficient to show that neutrinos violate CP - but that is incorrect.

CP violation is when you replace every particle with its antiparticle (C) and look at the resulting system in a mirror (P). CP violation means that you can tell the difference between the two systems

CP has been observed and is important because it's conjectured that the fact that the universe has more matter than anti-matter is a feature of CP violation.

Tim.

Re:Groundbreaking! Unprecedented! (3, Informative)

Anonymous Coward | more than 3 years ago | (#36471708)

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:Groundbreaking! Unprecedented! (1)

locofungus (179280) | more than 3 years ago | (#36471998)

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

Corrections (4, Informative)

Roger W Moore (538166) | more than 3 years ago | (#36472404)

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:Groundbreaking! Unprecedented! (0)

Anonymous Coward | more than 3 years ago | (#36473098)

CP violation was discovered in the 1960's or 1970's. CP violating Kaon decays have been studied to death. Are you trying to say something more profound?
Dragging out Yang-Mills, doesn't this just mean that neutrino masses are different? Same way that K_short and K_long masses differ? (Ex-particles guy -- been close to two decades since work in the field -- so maybe I'm missing something.)

Re:Groundbreaking! Unprecedented! (1)

Brucelet (1857158) | more than 3 years ago | (#36473846)

I think CP violation in the neutrino sector might have different physical implications than in kaons. It would certainly be dependent on a different set of mixing angles.

Re:Groundbreaking! Unprecedented! (1)

habig (12787) | more than 3 years ago | (#36474580)

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 way to earth (that's one of the sides). muon neutrinos are seen to change to tau neutrinos in Super-K's atmospheric neutrino signal and the MINOS accelerator experiment (that's the second side). This result is the first clear measurement of the third side, electron to muon changes. MINOS has made a similar but much messier measurement, T2K's is much cleaner.

CP violation is in the theory, but it's a second-order effect. That effect is multiplied by the size of this new electron/muon effect, so we need to measure this first, then we can look for "delta", the CP-violating phase.

(and yes, I Am a Neutrino Physicist - worked for many years on Super-K, now work on MINOS and Nova).

Tiny lil' bastards! (2)

Dutchmaan (442553) | more than 3 years ago | (#36471406)

Getting those little tags on em is a bitch!

Re:Tiny lil' bastards! (4, Funny)

Billlagr (931034) | more than 3 years ago | (#36471424)

I pity whoever has to catch them, then put those rings around their little legs

Re:Tiny lil' bastards! (2)

artor3 (1344997) | more than 3 years ago | (#36471770)

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.

slightly less than your average FedEx driver (0)

Anonymous Coward | more than 3 years ago | (#36472118)

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

Adventure. Heh. Excitement. Heh. A Jedi craves not these things.

Re:Tiny lil' bastards! (1)

pz (113803) | more than 3 years ago | (#36472630)

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.

Fukishima #1 and #3 Blowed Up Real Good (-1)

Anonymous Coward | more than 3 years ago | (#36471492)

News at 11 (JP time).

Ukraine called, said it wants their #1 asswipe country status back. Japan said, suck my dick. Ukraine called back, said, you call that a dick?

Mutant neutrinos! (0)

Anonymous Coward | more than 3 years ago | (#36471528)

How did they tell? cause the mutated nuetrinos dont have ears.

cheap brainetics (0)

brainetics (2263974) | more than 3 years ago | (#36471922)

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OH GOD (1)

Terranex (1500465) | more than 3 years ago | (#36472396)

THE NEUTRINOS HAVE MUTATED

Re:OH GOD (1)

Rogerborg (306625) | more than 3 years ago | (#36473034)

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:OH GOD (1)

Un pobre guey (593801) | more than 3 years ago | (#36476532)

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

Anonymous Coward | more than 3 years ago | (#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

Anonymous Coward | more than 3 years ago | (#36474608)

This, plus other particles that can mimic electron neutrinos, means that we were already expecting to see 1.5 background electron like events.

With 6 events seen and 1.5 expected we can say with 99.3% confidence that we have seen some of the muon neutrinos change into electron neutrinos.

Not to nit-pick too much, but shouldn't this read,

I'm also curious how you arrive at 99.3% exactly? :) A more accurate way could be "with at least 98% confidence, we have seen muon neutrinos change to electron neutrinos". This is assuming 2 for background and 6 result (Poisson distributions) and rounding off the "excess precision" of such a calculation.

Regardless, this is a significant result!

wdsci (1204512) | more than 3 years ago | (#36478048)

The 1.5 is a mathematical expectation value: if they could run this experiment a large number of times, there would be 1.5 events detected on average. Of course, all the physicists involved know that they are not actually going to see exactly 1.5 events. Still, it's more informative to write 1.5 than 1-2.

As far as the 99.3%, I'm not familiar with the specific statistical techniques involved, but if you look at the paper [arxiv.org] they do provide references [arxiv.org] that [arxiv.org] (I assume) explain how that 99.3% value can be obtained.

Anonymous Coward | more than 3 years ago | (#36474644)

Please mod parent up, +1 Informative.

For those who know some particle physics, it's a good and simple explanation.

Lawrence_Bird (67278) | more than 3 years ago | (#36476876)

Or look here. [science20.com]

Only one kind of neutrino? (0)

Anonymous Coward | more than 3 years ago | (#36473934)

So, if one neutrino can change into another type without any energy gain/release, then it must be only one type.

Not really "observed" either. (0)

Anonymous Coward | more than 3 years ago | (#36475170)

If I understand correctly, very much simplified it's more like counting the number of red cars going into a big tunnel, then counting where they exit and notice that there are now less red cars but more green cars coming out?

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