3 ms·
Opera detects its fifth tau neutrino
- TallGuyShort 11y agoAnyone know if this is this similar to the oscillation that many people think accounts for the surprising mass of the 125 Higg's reported at the LHC? I was surprised to read this as though it was something unique to neutrinos when I had heard that theory proposed before. (edit: mind you, I've only heard it as a possible explanation for Higgs bosons, whereas this is significant proof for neutrinos). For anyone interested, I recently finished Don Lincoln's "The Quantum Frontier: The Large Hadron Collider" and "The Large Hadron Collider" (they're kind of a series, although they have a lot of overlap). It's an excellent coverage of the theory and practice of particle physics, and although he doesn't cover the OPERA experiment at all,
- cshimmin 11y agoRegarding the Higgs mass, there are two basic camps in particle physics. Some believe the Higgs mass is just a constant of nature (just like the electron mass, or the speed of light), and there's nothing "surprising" about it, it's just what it is. Others believe that this mass is surprising because of "naturalness" issues -- the idea that this mass should have been more closely related to other fundamental constants, namely the Planck mass. However it is possible to view this suspicion as an aesthetic issue of the underlying mathematical framework (QFT). One of the main motivating features of Supersymmetry is to reconcile this difference by providing a mechanism by which the Higgs mass "naturally" becomes much less than the Planck mass. However many SUSY theories have been tightly constrained by recent experiments, requiring ever more contrived ways to cause this "natural" cancellation for a Higgs at 125 GeV. The oscillation of neutrinos is completely different. In the standard model of particle physics, neutrinos are treated as identically massless. However, experiments have shown that one flavor of neutrino can spontaneously transmute into another flavor. This phenomenon is (as far as we know) only possible if the neutrino has some (albeit tiny) mass. This has been observed extensively by other experiments that showed electron/muon neutrino oscillation, but OPERA is providing a direct measurement of muon->tau neutrino mixing.
- jabits 11y agoExcellent! Thanks.
- ars 11y agoHow can they tell it's from the beam and not from say, the Sun? Or other random galactic neutrinos?
- cperciva 11y agoI'm guessing the sun is easily ruled out based on the direction the neutrino was travelling (as measured by the momentum of the particle produced when the neutrino interacts with something). "Random galactic neutrinos" are probably a statistical exclusion: Although there could be a tau neutrino coming from the same direction as the experimental neutrino source, there aren't enough of them to create any significant chance of the observation being anything other than an experimental neutrino.
- cshimmin 11y agoThey do model backgrounds; the 5-sigma significance is a claim about the odds that background phenomena could have randomly caused this observation. However, their main backgrounds are not from the sources you mention. OPERA knows exactly what time the beam was on, and only considers data during that time <insert joke about that one time they thought neutrinos were traveling faster than light>. If galactic/solar tau neutrinos were present, they would see them all the time (not just when the beam was on), but they don't. That's not to say that they aren't there, but at the energies measured by the OPERA experiment, they would be exceedingly rare, especially compared to the high intensity of the neutrino beam they are receiving from CERN.