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 BB 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 → (cc)s transitions, and with the Standard Model expectation of small penguin contributions.