Revisiting D0-D0bar mixing using U-spin

We prove that $D^0$-$\bar D^0$ mixing in the standard model occurs only at second order in U-spin breaking. The U-spin subgroup of SU(3) is found to be a powerful tool for analyzing the cancellation of intermediate-state contributions to the $D^0$--$\od^0$ mixing parameter $y = ΔΓ/(2 Γ)$. Cancellations due to states {\it within a single U-spin triplet} are shown to be valid to first order in U-spin breaking. Illustrations are given for triplets consisting of (a) pairs of charged pions and kaons; (b) pairs of neutral pseudoscalar members of the meson octet; (c) charged vector-pseudoscalar pairs, and (d) states of four charged kaons and pions.

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