 Center-of-momentum frame

The center-of-momentum frame is an inertial frame in which the total spatial momentum of a system vanishes. For a two-particle initial state, the momenta are equal and opposite and the total invariant energy is $\sqrt{s}$.

The center-of-momentum (CM) frame, also known as the center-of-mass frame, is a specific reference frame used in physics, particularly in the study of collisions and particle interactions. In this frame, the total momentum of the system is zero. This means that the momenta of all the particles in the system balance out perfectly, resulting in a state where the center of mass is at rest.