Puzzling Lefthanded Neutrinos in Beta-Decay

[ulf.horsing]

I am puzzled by the "always lefthanded" neutrinos. In the beta-decay process a W-boson decays to an electron and an anti-neutrino, which must have same spin direction in order to comply with spin conservation. In the deay of a pion to a muon and an anti-muon neutrino these two particles must have opposite spin of the same reason. One may measure spin of electrons and muons but the spin of neutrinos can only be determined indirectly. Apparently this gives always lefthanded neutrinos, but how can you generalize from that to all neutrinos being lefthanded? Is it not possible for neutrinos to be produced in other rections than the beta-decay?

 

[diazona]

Not as far as we know. All experimental and theoretical evidence to date suggests that neutrinos have no electromagnetic charge and no color charge, so they're not subject to the strong or electromagnetic force. All that's left is the weak force, which is the force responsible for beta decay and similar reactions. So yes, there is only that one way to produce neutrinos.