# Positron decay direction from muon

• I
Hello! I read that in the rest frame of a positive muon, decay positrons are preferentially emitted in the direction of the muon spin. Why is that the case? The decay is ##\mu^+\to e^+\nu_e\bar{\nu_\mu}##. Assuming that the positron is emitted at almost the speed of light, it will be a left handed particle. The 2 muons are right handed and left handed. So we have a 3 body decay, with the 3 particles having their spin aligned or anti-aligned with their momentum. But I am not sure how can I get from here that the positron is more likely to be along the muon spin. Can someone help me? Thank you!

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Astronuc
Staff Emeritus
The 2 muons are right handed and left handed.
I believe one is referring to two neutrinos, or rather neutrino and antineutrino.

A muon decay positron is also correlated with the angular momentum of the muon in a more complicated way. Here, the positron with maximum energy takes the angular momentum of the decaying muon, since the left-handed electron neutrino and the right-handed muon antineutrino angular momenta cancel.
See slide 6 in https://www.triumf.ca/sites/default/files/sslec_201310.pdf

I believe one is referring to two neutrinos, or rather neutrino and antineutrino.

See slide 6 in https://www.triumf.ca/sites/default/files/sslec_201310.pdf