Which Lorentz transformation takes the lab system to the CM system?
Lab system: p_a = (E^{lab}_a, \vec{p}_a) and p_b = (m_b, \vec{0})
CM system: p_a = (E^{CM}_a, \vec{p}) and p_b = (E^{CM}_b, -\vec{p})
For a binary reaction a+b->c+d, the textbooks I have say quite a lot about the...