Limit of Energy in Lab Frame
The t quantity is known as the square of the 4-momentum transfer
[math]\displaystyle{ \mathbf P_1^2-2\mathbf P_1\mathbf P_1^'+\mathbf P_1^{'2} }[/math]
[math]\displaystyle{ \vartriangleleft }[/math] [math]\displaystyle{ \triangle }[/math] [math]\displaystyle{ \vartriangleright }[/math]