1. The problem statement, all variables and given/known data Earlier my teacher put this equation on the board, π_0 --> γ+γ It appears to work until you consider spin. 2. Relevant equations a quick google search reveals that the spin of a photon is +1 and the spin of a pi meson is 0 3. The attempt at a solution This appears to work for momentum, energy, charge, baryon number..... But π_0 has no spin and γ has a spin of +1. So in essence the atomic spin starts at 0 and finishes at +2. What am I missing?