Measurement of the time-dependent CP asymmetry of partially reconstructed B^{0}→D^{*+}D^{*-} decays

We present a new measurement of the time-dependent CP asymmetry of B0→D*+D*- decays using (471±5) million BB̄ pairs collected with the BABAR detector at the PEP-II B Factory at the SLAC National Accelerator Laboratory. Using the technique of partial reconstruction, we measure the time-dependent CP asymmetry parameters S=-0.34±0.12±0.05 and C=+0.15±0.09±0.04. Using the value for the CP-odd fraction R⊥=0.158±0. 028±0.006, previously measured by BABAR with fully reconstructed B0→D*+D*- events, we extract the CP-even components S+=-0.49±0.18±0.07±0.04 and C +=+0.15±0.09±0.04. In each case, the first uncertainty is statistical and the second is systematic; the third uncertainty on S + is the contribution from the uncertainty on R ⊥. The measured value of the CP-even component S+ is consistent with the value of sin2β measured in b→(cc̄)s transitions, and with the Standard Model expectation of small penguin contributions.