Study of the D^0 \to pi^-pi^+pi^-pi^+ decay

Using data from the FOCUS (E831) experiment at Fermilab, we present new measurements for the Cabibbo-suppressed decay mode $D^0 \to \pi^-\pi^+\pi^-\pi^+$. We measure the branching ratio $\Gamma(D^0 \to\pi^+\pi^- \pi^+\pi^-)/\Gamma(D^0 \to K^-\pi^+\pi^-\pi^+) = 0.0914 \pm 0.0018 \pm 0.0022$. An amplitude analysis has been performed, a first for this channel, in order to determine the resonant substructure of this decay mode. The dominant component is the decay $D^0 \to a_1(1260)^+ \pi^-$, accounting for 60% of the decay rate. The second most dominant contribution comes from the decay $D^0 \to \rho(770)^0\rho(770)^0$, with a fraction of 25%. We also study the $a_1(1260)$ line shape and resonant substructure. Using the helicity formalism for the angular distribution of the decay $D^0 \to \rho(770)^0\rho(770)^0$, we measure a longitudinal polarization of $P_L = (71 \pm 4\pm 2)$%.Comment: 38 pages, 8 figures. accepted for publication in Physical Review

Measurement of the doubly Cabibbo suppressed decay D-0 K+pi(-) and a search for charm mixing

We present an analysis of the decay D-0 -> K(+)pi(-) based on FOCUS data. From a sample of 234 signal events, we find a branching ration of Gamma(D-0 -> K(+)pi(-))/Gamma(D-0 -> K(-)pi(+)) = (0.429(-0.061)(+0.063) +/- 0.027)% under the assumptions of no mixing and no CP violation. Allowing for CP violation, we find a branching ration of (0.429 +/- 0.063 +/- 0.028)% and a CP asymmetry of 0.18 +/- 0.04. The branching ratio for the case of mixing with no CP violation is (0.381(-0.163)(+0.167) +/- 0.092)%. We also present limits on charm mixing