CM energy for different mass/energy beams

[penguindecay]

Dear Particle Physicist,

I'm unable to find an equation for the CM energy to use for when colliding beams have different masses and energies, for example the HERA colliding electron beams with proton beams. If you know a website, and can write the equation I'd be grateful. Thanks in advance

[Vanadium 50]

Just use E2- p2 = m2.

[Bob S]

Here is the 4-vector relativistic kinematic transformation:
http://pdg.lbl.gov/2009/reviews/rpp2009-rev-kinematics.pdf
Use equation 38.1.
Bob S