Neutrino Experiment Restores Standard Model Symmetry 83
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.
Some background (Score:5, Informative)
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)
Re:NOT good news! (Score:2, Informative)
Re:NOT good news! (Score:3, Informative)
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.
Re:The Electric Universe Theorists Called This One (Score:3, Informative)
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.
Hardly salvaged... (Score:3, Informative)
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)