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Neutrino Experiment Restores Standard Model Symmetry 83

Posted by kdawson
from the eightfold-way dept.
perturbed1 writes "A Fermilab press release announced that MiniBooNE's latest results have salvaged the Standard Model of particle physics. The experiment ruled out the simple neutrino oscillation interpretation of the 1990s LSND experiment. Neutrinos have a tiny amount of mass, required by their oscillations, as observed in solar, atmospheric, and reactor neutrino experiments. Combining this mass with the LSND experiment's results required the presence of a fourth but 'sterile' neutrino, breaking the 3-fold symmetry of particle families in the standard model." Nice to see some good news out of Fermilab after the CERN debacle.
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Neutrino Experiment Restores Standard Model Symmetry

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  • Some background (Score:5, Informative)

    by radtea (464814) on Thursday April 12, 2007 @09:56AM (#18701637)

    Neutrino oscillations are a process by which different types of neutrino can turn into each other. The elementary particles (quarks, leptons and neutrinos) all come in three "families". We are made of the lightest family: up and down quarks (which are the constituents of protons and neutrons) and electrons. Members of the heavier families are unstable and decay rapidly into lighter particles.

    However, it turns out that the weak nuclear interaction can mix quarks of different families. Down quarks turn out to be somewhat mixed with strange quarks of the next heaviest family due to this effect.

    For a variety of reasons, it was natural to ask if neutrinos were mixed in the same way. In particular, this could account for the unexpected deficit of electron-type neutrinos from the sun [queensu.ca]. Various terrestrial experiments were done in the 80's and 90's to try to detect this effect, including LSND.

    Neutrino experiments are extremely difficult and subject to all kinds of backgrounds, making them highly susceptible to errors in calibration and calculation. The LSND results were at odds with everything else that had been seen, but the stakes were high and no one wanted to give up on a result that might be right although it was not widely believed by people outside the LSND collaboration itself.

    The experiment described in TFA has tried to independently reproduce the LSND results. This is somewhat easier to do than the original experiment because you can design things so that you are most sensitive to the most interesting region. They have failed to find the effect that the LSND result would predict if it was due to neutrino oscillations, and it is likely that this is the end of it.

    The article never says so, but the most likely cause of the LSND result is some error in analysis, particularly in accounting for backgrounds and instrument effects. This kind of thing happens, particularly in neutrino physics, where the background processes are fundamentally many orders of magnitude stronger than the effects you are looking for, and have to be designed out with the most excruciating care.
  • Re:Good news (Score:2, Informative)

    by Dr_Mic (975409) <(ude.usp) (ta) (3grm)> on Thursday April 12, 2007 @10:29AM (#18702015) Homepage
    Actually, things without inertia (photons, for example) automatically go the speed of light. As a particle's energy increases (beyond rest mass energy), it becomes more "photon like" in that it asymptotically approaches the speed of light. So removing inertia will eliminate that inconvenient acceleration, but leave in place the ultimate speed limit.
  • Re:NOT good news! (Score:2, Informative)

    by Phleg (523632) <stephen@touset. o r g> on Thursday April 12, 2007 @11:12AM (#18702443)
    The problem is that as stated, the Standard Model and General Relativity are mutually exclusive. As they stand, both imply the invalidity of the other. But General Relativity is great for analyzing big things, and the standard model for extremely tiny things. Both make predictions with surprising accuracy. But as stated, they're incompatible.
  • Re:NOT good news! (Score:3, Informative)

    by shma (863063) on Thursday April 12, 2007 @12:12PM (#18703431)
    The way that we tell if a theory is broken is by experimentation.

    That is not entirely true. A theory which also gives infinite answers to certain questions, or answers which contract results from other (accepted) theories must be broken as well. For the standard model, however, we DO have results that conflict with observation. For example, there is the so called cosmological constant problem [wikipedia.org]. For GR, I assume the poster was referring to the problem of trying to integrate GR with quantum field theory. Most physicists accept that a full theory of the universe should describe gravity as a quantum phenomena.
  • by ZombieWomble (893157) on Thursday April 12, 2007 @01:13PM (#18704537)

    It appears that nobody seems to be asking the next logical question: if the neutrinos aren't there, then what about the Sun?

    Neutrinos are the required result of nuclear fusion within the Sun. They are not charged particles and they will travel through a light-year of lead. Now that Sudbury has been scrapped, there remains a severe deficit of neutrinos coming from the Sun for the nuclear fusion model.

    They're not asking the question because that is not at all what this result implies. This result does not rule out all neutrino oscillations, but rather deals with a specific result (produced at Los Alamos, not Sudbury) which significantly complicated the neutrino oscillation theory by requiring an additional fourth type of neutrino. The neutrino oscillation theory used to describe the yield of various species from the sun is still quite intact, I believe.
  • Hardly salvaged... (Score:3, Informative)

    by Roger W Moore (538166) on Thursday April 12, 2007 @01:23PM (#18704715) Journal
    Firstly nobody really believed he Los Alamos results principly because some of the collaborators removed their names from the original results paper and published another paper in the same journal issue in which they voiced considerable concern over the validity of the results. If you can't convince your own collaborators it is very hard to convince anyone else.

    Secondly neutrino oscillations are not in the Standard Model and the problem with the LSND result was that it could not be reconciled with the other neutrino mising results from SNO and SuperK. So while this results is still very interesting it simply confirms that a simple neutrino mixing EXTENSION to the the Standard Model may be sufficien without needing to invoke more exotic alternatives.
  • Clarification (Score:5, Informative)

    by perturbed1 (1086477) on Thursday April 12, 2007 @02:20PM (#18705689)
    I submitted this story to Slashdot, but sadly, I see that my original wording has been altered by kdawson. Unfortunately, I do not have a copy of my original post, but I would like to clarify what I *meant*. First of all, I do not consider this "good news" -- but "good results." The MiniBooNE team clearly worked very hard to get here so a big "Congrats" goes out to them. You could not rule out the LSND result, just because "we did not expect it" and "found it fishy." The unexpected results are sometimes the best ones and in science, remember: one scientist's junk is another scientist's signal. The CMB discovery story [wikipedia.org] is the best example to this. Secondly, the neutrino mass indeed does not belong in the standard model, which already several people have pointed out. What belongs in the standard model is the number of lepton families. It is good to see it confirmed that no "sterile" neutrino is needed to explain the results. Yes, cosmologists have had some say in the subject matter already, but it is good to see it confirmed. This is, afterall, how physics is done. "I told you so" is never a good thing to say in physics. You never know what comes out next afterall. I do not believe that Standard Model has been salvaged by this result nor do I want to live with the Standard Model for the rest of my life. There is already plenty of evidence that the Standard Model is not a sufficient model for explaining all the physical phenomena we observe and soon, I hope soon we will have evidence what that new "something" might be. At this point, I would also like to take this chance, as a physicist who works at CERN, to reply to the highly excited conspiracy theorists: Calm down! CERN, Fermilab and other physics labs are not part of corporate America! Yes, of course, I want CERN (and my experiment, in specific) to be the one who finds the Higgs, but I am willing to bet all my fortune, little as that may be, on that Fermilab's calculation mistake was not intentional. Yes, we, physicists are a funny bunch, with lots of things to argue and get excited about. But, we do have a common goal in life, to dig deeper into the mystery of the universe. And a common understanding -- that the truth *will* reveal itself and you can not determine when it does.

There is no royal road to geometry. -- Euclid

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