John Clark wrote:
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> Joseph C Fineman <email@example.com> Wrote:
> >Antineutrinos exist in any case.
> Yes, they were actually discovered experimentally before neutrinos were.
> >They are distinguished from neutrinos by their helicity (direction
> >of spin relative to their direction of motion). When a neutron decays,
> >for example, it yields a proton, an electron, and an antineutrino.
> >However, it seems to me that if neutrinos have rest mass, this
> >distinction must in principle lapse, since you can then choose a
> >frame of reference in which the helicity is reversed.
> You can't turn a right hand glove into a left one in any frame of
> reference, at least not if you stay in 3 dimensions; you'd have to
> flip it around in the fourth spatial dimension. Besides, the two
> particles act differently. A antineutrino is absorbed (rarely) by a
> proton which turns into a neutron and a positron (also called a
> anti electron), a neutrino is absorbed (rarely) by a neutron which
> turns into a proton and a electron.
Which if you put on a Feynman chart are the same reaction when you reverse the time component. In reverse, the neutrino will seem to be absorbed by the proton while emitting a neutron and an anti-electron (the eletron going backwards in time).