1. The problem statement, all variables and given/known data When a beam of high-energy protons collides with protons at rest in the laboratory (e.g., in a container of water or liquid hydrogen, neutral pions are produced by the reaction p+p --> p+p+(pion). Compute the threshold energy of the protons in the beam for this reaction to occur. 2. Relevant equations I don't even know where to start with this one. 3. The attempt at a solution All attempts I've made are ridiculous because I didn't even know what equations to start with.