Measurement of cos⁡2β in B^{0}→D^{(*)}h^{0} Decays with a Time-Dependent Dalitz Plot Analysis of D→K_{s}^{0}π^{+}π^{-}

We study the time-dependent Dalitz plot of D→KS0π+π- in B0→D(*)h0 decays, where h0 is a π0, η, η′, or ω meson and D*→Dπ0, using a data sample of 383×106 Υ(4S)→BB̅ decays collected with the BABAR detector. We determine cos⁡2β=0.42±0.49±0.09±0.13, sin⁡2β=0.29±0.34±0.03±0.05, and |λ|=1.01±0.08±0.02, where the first error is statistical, the second is the experimental systematic uncertainty, and the third, where given, is the Dalitz model uncertainty. Assuming the world average value for sin⁡2β and |λ|=1, cos⁡2β>0 is preferred over cos⁡2β<0 at 86% confidence level.