Proton/Antiproton collision to produce top/anti-top quark pair:

[eden2291]

Consider a proton and antiproton collision. The goal is to produce a top quark and anti-top quark pair. If a top quark has a mass of 174 GeV/c², how much energy is required in the center of mass frame to produce the combination?

I'm somewhat utterly stumped. Obviously, the problem deals with a collision (I'd assume inelastic since the pair derived from the collision is a single mass?) in which relativistic principles need to be taken into consideration. So, my feeble initial attempt is to find the initial versus final mass, wherein:
Minitial=2(proton mass)
Mfinal=2(top-quark mass)
And then compensate for the increase in energy by finding the kinetic energy of the colliding protons. But again, this is little more than a guess.

THANKS FOR THE HELP!

 

[fzero]

Suppose that the top and anti top have equal and opposite momenta. Further suppose that the magnitudes of their momenta is very small compared to their mass. What is the center of mass energy in the final state?