Resonance channel threshold conversion ($T_b^{\ast }=T_a^{\ast }+(m_{a1}+m_{a2}-m_{b1}-m_{b2})c^2$)

The same compound-state energy is measured from different rest-energy thresholds in different entrance channels. Subtracting those thresholds converts the required centre-of-momentum kinetic energies. For a stationary target and nonrelativistic projectile, the laboratory kinetic energy is $T_{\mathrm{lab}}=T^{\ast }(m_{\mathrm{projectile}}+m_{\mathrm{target}})/m_{\mathrm{target}}$. A negative converted $T^{\ast }$ means that entrance channel is closed at that resonance energy.