At LEP, electrons and positrons, each of energy E= 45.6 GeV (I guess this is total since it's a particle physics course), are collided head-on, and have exactly the right energy to produce Zo particles at rest. [tex]e^+ e^- = Z_0 [/tex] This is simple but I'm having a bit of trouble with collisions. The particles initially have total energy [tex]2E= 2(\gamma)m_ec^2 [/tex], since Z will be be created at rest all of this energy will go into the creation of mass of Z. To what energy would a positron have to be accelerated if in collision with a stationary atomic electron it were to produce a Z0? The kinetic energy [tex] T = (\gamma - 1) m_ec^2 [/tex] [tex]2(\gamma)m_ec^2 = m_Zc^2 [/tex] [tex]2E = (\gamma - 1) m_ec^2 + 2m_ec^2 [/tex] [tex]2E = T + 2m_ec^2 [/tex] [tex]T = 2E - 2m_ec^2 [/tex] = 2(45.6 eV) + 2(0.511) = 92.2 ev I'm not really sure if my thinking is right here, I've basically ignored Z.