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Muon Neutrino To Electron Neutrino Oscillation Conclusively Shown
New submitter Chris Greenley writes "The T2K long baseline neutrino experiment in Japan has just announced conclusive evidence for electron to muon neutrino oscillation at the 7.5 sigma level. (The level needed for discovery is 5 sigma.) This experiment generates a focused beam of electron neutrinos using an accelerator in the J-PARC facility north of Tokyo which is aimed at the massive Super-Kamiokande detector 295 km (185 miles) away, near the west coast of Japan. 'This T2K observation is the first of its kind in that an explicit appearance of a unique flavor of neutrino at a detection point is unequivocally observed from a different flavor of neutrino at its production point.' This result clears the way for CP-violation neutrino studies which could show that 'regular' neutrinos act differently than their antimatter counterparts, a phenomenon that so far has only been observed in quarks. If neutrino CP-violation is found, it could explain why there is such a large predominance of matter over antimatter in the universe."
It's only obvious in SU(5). The currently en-vogue SU(2)+SU(3) lie groups only imply it. But you knew that right?
They detected 28 electron neutrino interactions, where they would have expected 5 such events without the oscillation in question. This helps underscore how incredibly hard is it to get neutrinos to show up with anything: even when one is manufacturing millions of them, one is lucky to get a tiny set to then show up in your detector. This is connected to how most neutrino detectors are basically large vats of water or some other liquid, because the most we can generally hope for is that if we put enough mass in the way, some neutrinos will by sheer chance run into things.
This is also relevant to what we expect for stellar neutrino observation. Understanding neutrino oscillation gets us a better idea of what sort of neutrino ratios to expect (as a function of energy levels) in other circumstances. Right now, we can observe a lot of natural neutrinos from the sun. But the only neutrinos we've observed from an identified extra solar location, the 1987A http://en.wikipedia.org/wiki/SN_1987A, which was a very close supernova (so close it could be seen with the naked eye). In fact, in that case, the neutrinos arrived before we saw the light. That's not at all connected to the erroneous claim from a few years ago that neutrinos were going faster than light speed. What is happening here is that most of the light in a supernova is formed in the core, and the core of a star is very dense. So it takes a long time for the light to reach the surface of the star. But from the standpoint of neutrinos even very dense star isn't that much of an issue so they can get to the surface much faster. It is possible that this sort of work will give us better understanding both such neutrinos and what to expect when we do observe them from other close supernova.
Neutrinos are still a major area where there's a lot we don't understand, and this research is going to possibly have major implications for our understanding of these elusive particles.
This explanation is insufficient. If neutrinos were indeed massive particles we'd see a wide distribution of their velocities, just like we can observe slow and fast protons, slow and fast electrons, slow and fast everything that moves slower than c. Yet, in 100% of experiments that have been done all neutrinos are propagating through space at the speed close to or exactly equal to c.
The reason for this is the extremely small mass of neutrinoes. The current experimentally-derived upper bounds on their mass is around 1 eV (in contrast, an electron has a mass of 511,000 eV). This means that any process that creates a neutrino will give it enough energy to send it off at ultrarelativistic speeds. Even something simple like neutron decay can impart 1 MeV of kinetic energy to a neutrino, which, as the grandparent calculates, means the neutrino is traveling at 0.999999999999*c. Only chemical reactions would release a small enough amount of energy to have non-relatvistic neutrinos. But, chemical reactions don't release neutrinos.
This is why we only see speed-of-light neutrinos. This is also why it's taken so long to discover that they have mass.
This explanation is insufficient. If neutrinos were indeed massive particles we'd see a wide distribution of their velocities, just like we can observe slow and fast protons, slow and fast electrons, slow and fast everything that moves slower than c.
That's completely mistaken. We don't find a wide distribution of neutrino velocities because it takes very little energy to make a neutrino go very close to the speed of light (this happens because neutrinos have *very* little mass). This means that there's a very small probability for a neutrino to have a small velocity relative to anything else -- you just have to sneeze at it (that is, interact with it in almost any way) to send it flying away at close the speed of light. So it's *expected* that you'll never actually see a slow neutrino.
There is already too much evidence against Relativity Theory as it presently is.
That's just bullshit. It's true that General Relativity doesn't fit at all with Quantum Mechanics, but there's *no* compelling evidence at all against Relativity (either General or Special). There's *no* known experiment that gives a conclusive result that's different from what Relativity predicts. People are working on other theories because General Relativity doesn't fit with Quantum Mechanics, not because there's evidence against Relativity.
It's true that General Relativity doesn't fit at all with Quantum Mechanics
That is overstating things a bit. For the most part, GR and things like QFT get along just fine, and it helps that space-time in GR is locally pretty flat most of the time. And some work comes from just using them together anyways. There are some obvious conflicts (although some I think are more for idealogical reasons than experimental reasons), but it comes down to specific situations, which is part of the difficulty of testing proposed replacements.