October 1, 2012 The Guardian UK
Last week’s results from the Daya Bay neutrino experiment were the first real measurement of the third neutrino mixing angle, θ13 (theta one-three). There have been previous experiments which set limits on the angle, but this is the first time it has been shown to be significantly different from zero.
Since θ13 is a fundamental parameter in the Standard Model of particle physics1, this would be an important measurement anyway. But there’s a bit more to it than that.
Neutrinos – whatever else they might be doing – mix up amongst themselves as they travel through space. This is a quantum mechanical effect, and comes from the fact that there are two ways of defining the three types of neutrino.