As we know photon's helicity are [itex]\pm[/itex]1. Helicity is the projection of the spin S onto the direction of momentum, p, which is considered as S(adsbygoogle = window.adsbygoogle || []).push({}); _{z}.

What about S_{x}and S_{y}? They are both ZERO?

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# Helicity is different form Spin for massless particle(photon)?

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