Study of the decay mode D^0 -> K-K+pi-pi+
  Using data from the FOCUS (E831) experiment at Fermilab, we present a new measurement of the branching ratio for the Cabibbo-favored decay mode $D^0 \to K^-K^+\pi^-\pi^+$. From a sample of $2669 \pm 101$ fully reconstructed $D^0 \to K^-K^+\pi^-\pi^+$ events, we measure $\Gamma(D^0 \to K^-K^+\pi^-\pi^+)/\Gamma(D^0 \to K^-\pi^-\pi^+\pi^+) = 0.0295 \pm 0.0011(stat.) \pm 0.0008(syst.)$.   A coherent amplitude analysis has been performed to determine the resonant substructure of this decay mode. This analysis reveals a dominant contribution from $D^0 \to K_1^+ K-$ modes. 
the FOCUS Collaboration: J.Link, et al