The (549) meson has spin-0 and is observed to decay to three-pion final states by the electromagnetic

The η(549) meson has spin-0 and is observed to decay to three-pion final states by the electromagnetic processes (5.57b) and (5.57c). Use this information to deduce the parity of the η, and hence explain why the decays η → π ⁺ π⁻ and η → π⁰π⁰ have never been observed. 

Equation 5.57b

η → π⁰ + π⁰ + π⁰, B = 0.33, (5.57b)

Equation 5.57c

η → π⁺ + π⁻ + π⁰, B = 0.23. (5.57c)