The resonant substructures of \Dz→\fourpi and \Dz→\KKpipi decays are studied using data collected by the CLEO detector. Amplitude analyses are performed using a data driven regularization procedure to limit the model complexity. For the \Dz→\fourpi decay the prominent contributions are the decay modes \Dz→a1(1260)+π−, \Dz→σf0(1370) and \Dz→ρ(770)0ρ(770)0. The broad resonances a1(1260)+, π(1300)+ and a1(1640)+ are studied in detail, including quasi-model-independent parametrizations of their lineshapes.
The amplitude analysis of \Dz→\KKpipi decays uses a significantly improved formalism with respect to previous analyses of the decay. The largest contributions to the decay are found to be the decay modes \Dz→ϕ(1020)ρ(770)0, \Dz→K1(1270)+K− and \Dz→K(1400)+K−. A search for \CP asymmetries at both global and amplitude component level yield no evidence for \CP violation in either decay mode.\\
The work presented here is published in Ref.~\cite{dArgent2017}.