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Indication of Neutrino Transformation Observed

Posted by timothy on from the you-become-the-particle-you-want-to-be dept.

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."

27 of 128 comments (clear)

  1. proof by Dr+Max · · Score: 3, Interesting

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

    --
    Rocket Surgeon.
    1. Re:proof by global_diffusion · · Score: 2

      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.

    2. Re:proof by davester666 · · Score: 2

      So, it just 'probably' happened?

      --
      Sleep your way to a whiter smile...date a dentist!
    3. Re:proof by global_diffusion · · Score: 2

      :)

      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).

    4. Re:proof by Billlagr · · Score: 2

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

    5. Re:proof by Entropius · · 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.

    6. Re:proof by dido · · Score: 4, 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 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.

      --
      Qu'on me donne six lignes écrites de la main du plus honnête homme, j'y trouverai de quoi le faire pendre.
    7. Re:proof by Artifakt · · Score: 3, Insightful

      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.

      --
      Who is John Cabal?
    8. Re:proof by Anonymous Coward · · Score: 2, Informative

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

    9. Re:proof by artor3 · · 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

    10. Re:proof by Shimbo · · Score: 4, 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.

    11. Re:proof by AlecC · · 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.

      --
      Consciousness is an illusion caused by an excess of self consciousness.
    12. Re:proof by Tim+C · · Score: 3, Insightful

      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)

      --
      It's official. Most of you are morons.
    13. Re:proof by Anonymous Coward · · 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.

    14. Re:proof by siglercm · · Score: 2

      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.

      --
      sigfault (core dumped)
  2. Groundbreaking! Unprecedented! by pushing-robot · · Score: 4, Informative

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

    Oh, really?

    --
    How can I believe you when you tell me what I don't want to hear?
  3. Tiny lil' bastards! by Dutchmaan · · Score: 2

    Getting those little tags on em is a bitch!

    1. Re:Tiny lil' bastards! by Billlagr · · Score: 4, Funny

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

    2. Re:Tiny lil' bastards! by artor3 · · 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.

  4. Re:Groundbreaking! Unprecedented! by locofungus · · Score: 3, 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.

    --
    God said, "div D = rho, div B = 0, curl E = -@B/@t, curl H = J + @D/@t," and there was light.
  5. Re:Groundbreaking! Unprecedented! by Anonymous Coward · · Score: 3, Informative

    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

  6. Re:How can they detect anything at all? by evanoc · · 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.

  7. Re:How can they detect anything at all? by artor3 · · Score: 2

    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.

  8. Re:Groundbreaking! Unprecedented! by locofungus · · Score: 2

    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.

    --
    God said, "div D = rho, div B = 0, curl E = -@B/@t, curl H = J + @D/@t," and there was light.
  9. Corrections by Roger+W+Moore · · Score: 4, Informative
    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.

  10. Neutrino absorption by OeLeWaPpErKe · · Score: 2

    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.

  11. More Information by Anonymous Coward · · 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