# Why is 3 pion decay of eta (η) strong forbidden?

by Smithf
Tags: η, decay, forbidden, pion, strong
 P: 5 I have read that 3 pion decay of the eta is not allowed as a strong reaction, but proceeds as an electromagnetic interaction. I do not see why it is strong forbidden.
 Sci Advisor P: 1,233 That is easiest to see using G parity, which is $$C e^{i\pi I_y}$$. One or three pions have negative G, while the eta has positive G.
 P: 5 How do you find the result of the I2 rotation operation?