Indication of Neutrino Transformation Observed 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."
Groundbreaking! Unprecedented! (Score:5, Informative)
observed for the first time an indication that a type of neutrino can change into another type
Oh, really? [wikipedia.org]
Re:proof (Score:5, Informative)
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:Groundbreaking! Unprecedented! (Score:4, Informative)
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:proof (Score:5, Informative)
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:Groundbreaking! Unprecedented! (Score:3, Informative)
Re:proof (Score:2, Informative)
They don't need to measure the type of neutrinos they're emitting, they already know what type they are.
Re:proof (Score:5, Informative)
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 (Score:2, Informative)
Re:proof (Score:5, Informative)
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.
Corrections (Score:5, Informative)
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 (Score:4, Informative)
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:proof (Score:2, Informative)
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.