Talk:Threshold energy

There's an easier way to derive this. Using Lorentz invariance of the square of the total four-momentum along with conservation of momentum, we have $$p_{\mathrm{tot},i}^2 = p_{\mathrm{tot},f,cm}^2$$. Plugging in the threshold values for the final 4-momentum in the CM frame (rest mass energies, zero total momentum), and the energy equation $$E_1^2 = m_1^2 + \vec p_1^2$$, the momentum terms cancel and we are left with the equation for $$E_1$$. --Babomancer (talk) 02:10, 12 December 2014 (UTC)