# I Does beta decay change spin orientation?

1. Mar 27, 2017

### jerry mac

If you have a free neutron viewed from a known frame of reference which is known to be spin up and it decays, is there anything in theory or experiment which indicates whether the remaining proton will be spin up or down? Thanks Jerry

2. Mar 28, 2017

### ChrisVer

no, the proton can be up or down, depending on the electron and neutrinos' momenta...

3. Mar 28, 2017

### jerry mac

Thanks for the response. In popular accounts of decay, spin is not usually discussed and I am trying to understand it. I guess in order to emit a w minus particle there would be handedness change internally as the down quark changes into an up quark, but that wouldn't change the overall spin orientation of the nucleon.

4. Mar 29, 2017

### ChrisVer

the spin is conserved... so you don't have to think in terms of the W bosons...
initially you had +1
in the final state you must also have +1
Now the final state consists of the proton, electron and electron antineutrino
some combinations showing the up/down of proton's spin would be: $+1_p + 1_e - 1_\nu$ or $-1_p + 1_e + 1_\nu$...
Now of course antineutrinos have right handed helicity, and so them having + or - spin depends on their momentum orientation...
If the antineutrino has spin -1, it should also move towards the negative z-axis, if it has +1 it will move towards the positive z-axis (so that the spin and momentum are alligned).

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