In modern collider experiments the beam energy K has much greater energy than its rest e...

In modern collider experiments the beam energy K has much greater energy than its rest energy (K >> mc ² ) . If two particles each of mass m collide head-on with each having beam energy K, the energy in the center of mass E_cm = 2K. Show that two particles of the same mass m colliding head-on with each having kinetic energy K (K >> mc ² ) have the same center-of-mass energy as the same particle of energy K_lab in a fixed-target accelerator colliding with the same target particle, where