1. The problem statement, all variables and given/known data An incident positron (e+) with rest mass m_e and with energy E strikes an electron (e−) at rest, also with rest mass me. They annihilate such that the liberated energy produces a top quark (t) and an anti-top quark (ṯ), each with rest mass of m_t. Find an expression for the minimum incident energy E of the positron that will allow this reaction to happen. 2. Relevant equations E^2 = P^2*m^2 + m^2*c^4 3. The attempt at a solution I know I'm supposed to use the center of mass reference frame somehow, but I don't really have any idea how that helps. Can somebody please point me in the right direction? Edit: I got it. Please ignore this post.