The most common particle in the Universe is also the most mysterious, but it seems that scientists might have got something correctly predicted about it. Neutrinos have been noticed to disappear’ in the Double Chooz experiment and this is being interpreted as the manifestation of the elusive neutrino oscillation signature. Electron anti-neutrinos have been noticed to simply disappear meaning that they are actually turning into tau anti-neutrinos, which we have no way of detecting. Technically, scientists are measuring the third mixing angle’ or Î¸13.
Oscillations of neutrinos
Neutrinos are strange because they do not behave in conventional’ ways. One form of neutrinos can change into another, provided neutrinos have mass, however small it might be. There are three types of neutrinos electron neutrinos, muon neutrinos and tau neutrinos. The names are given according to the particle they accompany in a doublet.
Experimental evidence suggests that one form of neutrinos changes into another and this is through a process called see-saw’ mechanism. In other words, the neutrino exists in a mixed’ state and we detect only one of the constituent states. (If you think this is weird, just know that this is the staple bread-butter of quantum mechanics.) The amount of mixing is given by angles. The electron (type 1) and muon (type 2) type neutrinos mix via the mixing angle Î¸12. The muon (type 2) and tau (type 3) neutrinos mix via the Î¸23 angle. The electron and the tau neutrinos mix via the angle Î¸13, which happens to be out angle of interest. We know that Î¸13 is very small, but we want to know how small it really is. The fact that it is non-zero is, in itself, remarkable.
The value of the mixing angle and the consequence of that
One of the experiments measuring the Î¸13 is the Double Chooz experiment. It just released the first set of results and it gives a definitive value for this third mixing angle. The value, given in terms of sine squared of double the angle, is
sin22Î¸13 = 0.085 + 0.029(stat) + 0.042(syst),
where the last two numbers represent errors and need not concern us too much at the moment.
What is interesting is the fact that the other giant experiment in the field of neutrinos the T2K experiment also gives similar results.
The value of Î¸13 is not zero and the two results corroborate one another to give a 3-sigma level confidence on that fact. There are neutrino oscillations between the electron type and the tau type.
This is a theoretically significant result for scientists, who are knee-deep with questions about neutrinos and their properties (and, before you ask, the faster-than-light results are the least of the worries). This will put further constraints on the neutrino masses.