Symmetries in particle physics
Symmetries in particle physics
Symmetries in particle physics
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Discrete symmetries:<br />
Parity<br />
Helicity, chirality, and all that<br />
In the Standard Model:<br />
ALL NEUTRINOS ARE LEFT-HANDED<br />
This can be seen by consider<strong>in</strong>g pion decays <strong>in</strong>to<br />
muon + ant<strong>in</strong>eutr<strong>in</strong>o. In the rest frame of the pion,<br />
the muon and neutr<strong>in</strong>o come out back-to-back and<br />
the sp<strong>in</strong>s have to add to 0 (s<strong>in</strong>ce the pion has<br />
sp<strong>in</strong>-0). Therefore, the handedness (sp<strong>in</strong>-direction) of<br />
the anti-neutr<strong>in</strong>o equals the handedness of the muon.<br />
In this experiment, up to now, muons with only one<br />
helicity/handedness have been found.