# B Neutral pion decay

1. Apr 2, 2016

### simon96c

Hi everyone,
I am curious about how a neutral pion decays in two photons. I don't understand how it is possible since the pion has spin = 1 and the photons have spin = 1 as well: doesn't this mean that spin is not conserved in this decay? What am I missing?

Another question I have is about spin: do anti-particles and anti-quarks have negative spin, or is the spin always positive?

Sorry for the silly questions and thanks to everyone in advance :)

2. Apr 2, 2016

### PeroK

Perhaps the pion doesn't have spin 1? If the pion has spin 0, say, that might indeed make it a silly question.

3. Apr 2, 2016

Staff Emeritus
How sure are you that the pion has spin 1?

4. Apr 2, 2016

### Orodruin

Staff Emeritus
Apart from this, it is perfectly possible for two spin-1 particles to couple to a spin-1 so even if the pion had spin 1 it would not be that strange.

5. Apr 2, 2016

Staff Emeritus
Actually, a spin-1 particle cannot decay to two photons. See Yang, Physical Review 77: 242–245 (1950).

6. Apr 2, 2016

### Orodruin

Staff Emeritus
Not disputing that. All I am saying is that it is not as easy as saying $1+1 \neq 1$.