# Initial CM Frame 4-momentum components

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# Initial CM Frame 4-momentum components

Figure 2: Definition of variables in the Center of Mass Frame

Starting with the definition for the total relativistic energy:

Since we can assume that the frame of reference is an inertial frame, it moves at a constant velocity, the mass should remain constant.

We can use 4-momenta vectors, i.e. ,with c=1, to describe the variables in the CM Frame.

Using the fact that the scalar product of a 4-momenta with itself,

is invariant.

Using this notation, the sum of two 4-momenta forms a 4-vector as well

The length of this four-vector is an invariant as well