1. The problem statement, all variables and given/known data A 2 GeV electron is incident on proton (m_p * C^2 = 0.938 GeV) target at rest. Calculate the invariant mass of the electron-proton pair in the Center of Mass(CM) frame. Neglect the mass of electron which is much less than the proton mass. 2. Relevant equations M = [P1 + P2)][/2] M = gamma([m][/0]) 3. The attempt at a solution My first attempt was to calculate the mass through the second equation in relevant equations but I don't think that was correct. Because it went like this: M = ([m][/0])/sqrt(1-(([v][/2])/[c][/2]) but I don't think that is necessarily the right step forward. Any help would be much appreciated!