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

by time601
Tags: form, helicity, massless, particlephoton, spin
 P: 8 As we know photon's helicity are $\pm$1. Helicity is the projection of the spin S onto the direction of momentum, p, which is considered as Sz. What about Sx and Sy? They are both ZERO?