= Dalitz boundary from pair-rest-frame kinematics
{c}
{title2=$s_{23}^\pm=m_2^2+m_3^2+2(E_2^*E_3^*\pm p_2^*p_3^*)$}
At fixed $s=s_{13}$, use $E_2^*=(M^2-m_2^2-s)/(2\sqrt s)$ and $E_3^*=(s+m_3^2-m_1^2)/(2\sqrt s)$ in the 13-pair rest frame. The endpoint values of its relative cosine give the displayed <Dalitz plot> boundary. The <momenta> are fixed by the <Källén function>; $(m_1+m_3)^2\le s\le(M-m_2)^2$. Integrating $s_{23}^+-s_{23}^-$ gives the <Dalitz plot>[invariant-coordinate area], whose <Lorentz-invariant phase space>[phase-space] <normalization> still contains $M^{-2}$.
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