Finite-width effects in resonance decay near threshold

The decay of a resonance into a final state containing two particles, the sum of whose mean masses exceeds that of the parent particle, is investigated. Alternative methods for calculating the transition rate are compared. Two specific decays, $Y_0\mathrm{}\left(1518\right)\mathrm{}\to Y_1\mathrm{}\left(1385\right)\mathrm{}\pi$ and $A_2\mathrm{}\left(1310\right)\mathrm{}\to B\left(1237\right)\mathrm{}\pi$, are studied numerically.