Re: Neutrinos

John Clark (
Wed, 18 Aug 1999 12:28:49 -0400

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Joseph C Fineman <> Wrote:

>Its [the neutrino's] handedness is determined by its spin _relative to
>its momentum_. If its rest mass is zero, that is an unambiguous
>definition, because there is no frame of reference in which the
>momentum is reversed. But if the neutrino as a rest mass, then it has
>a rest frame, in which its momentum is zero, and the helicity is not
>even defined. Its spin, presumably, can be in any direction whatever.

Spin is a function of angular momentum not linear momentum. The spin of a neutrino can be of only two values, +1/2 or - 1/2, it's called the spin up and the spin down orientations and exactly the same thing is true of a antineutrino. The difference between the neutrino and the antineutrino is in the polarity of their magnetic field. Of course sub atomic particles don't really spin in the same way that balls do but a good analogy is that If both particles are spin up and you look at the pole of the neutrino that makes the particle look like it's rotating counterclockwise then that's the north magnetic pole, on the antineutrino it's the south.

John K Clark

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