1. The problem statement, all variables and given/known data Positronium is formed by stopping anti-electrons in matter. It is found that the bound system is formed in two distinct states, both of which have orbital angular momentum [tex] $ L = 0 $ [/tex]. Consider the possible spin configuration of this system, to determine the expected total angular momentum for these two positronium states. 2. Relevant equations Not sure. Selection rules? 3. The attempt at a solution Here is what I wrote down, lol: [tex] \mid +,\uparrow \rangle \otimes \mid -,\downarrow \rangle [/tex] [tex] \mid +, \downarrow \rangle \otimes \mid -,\uparrow \rangle [/tex] Im not sure if these are right or relevant though. It seems to me the answer is zero, does that sound right? Is there a way I can show this?