Natural parity
= Natural parity
{title2=$\pi=(-1)^J$}
For a state of integer total <angular momentum> $J$, natural <parity> means $\pi=(-1)^J$: $0^+,1^-,2^+,3^-,\ldots$. The other sign is called unnatural parity. The terminology is useful when a spin-zero positive-parity parent emits a spin-zero positive-parity particle: <angular momentum conservation> fixes relative <orbital angular momentum> $L=J$, and <parity conservation> then forces natural parity for the daughter.