= Cabibbo hierarchy of neutral-D two-body decays
{c}
In the charged-current spectator topology $c\to qW^+$, $W^+\to u\bar q'$, the magnitudes of the CKM factors give favoured, singly suppressed and doubly suppressed amplitudes of orders $1$, $\tan\theta_C$ and $\tan^2\theta_C$. Squaring gives rate orders $1$, $\tan^2\theta_C$ and $\tan^4\theta_C$. Two singly suppressed channels are not thereby predicted to have equal rates: hadronic matrix elements, <phase space> and rescattering can differ.
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