1. The problem statement, all variables and given/known data How much photon energy would be required to produce a proton-antiproton pair? Give the answer in SI units. 2. Relevant equations E^2=p^2c^2+m^2c^4 E=pc+pc p=mc E=2*m*c^2 3. The attempt at a solution I seem to be confused I know the KE would be zero I also know this would not exist in real life but I need to find the min energy so KE of the photon pairs is 0. I am not sure if the equation has to do with the mass of a photon or the momentum of the photons. In either case I don't know what the mass of a photon would be. I read it was zero but can't figure out how to use this formula then.