Indication of Neutrino Transformation Observed

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."

Comments

proof

[Dr Max]

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

Re:proof

[Entropius]

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

[dido]

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 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 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

[Artifakt]

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

[artor3]

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

Re:proof

[Shimbo]

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

[Tim C]

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)

Groundbreaking! Unprecedented!

[pushing-robot]

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

Oh, really?

Re:Tiny lil' bastards!

[Billlagr]

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

Re:Groundbreaking! Unprecedented!

[locofungus]

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!

[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

Corrections

[Roger W Moore]

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.

More Information

[Anonymous Coward]

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