In the book A Introductory Course Of Particle Physics by Palash B. Pal, the author claims the following (on page 167, section 6.4.3)
For single-particle systems, intrinsic parity is the only contribution to parity. For multi-particle systems, however, there are other contributions.
However, in addition to intrinsic parity coming from spin, orbital parity can arise for single-particle states if it carries an orbital angular momentum such as photons. See the questions below
- What is the orbital angular momentum (OAM) of individual photons?
- Does orbital angular momentum has no meaning for single photons?
Is it true that for single-particle systems, intrinsic parity is the only contribution to parity?