Two-body kinematics

$$\begin{eqnarray*}M^2 &=& \left( E_1 + E_2 \right) ^2 - \left( \vec{p_1}+\vec{p... ...eft( \frac{\vec{p}_1}{T_1} - \frac{\vec{p}_2}{T_2} \right) ^2 \end{eqnarray*}$$