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

Abstract

We present a new measurement of the time-dependent CP asymmetry of B^0→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 B^0→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 sin⁡2β measured in b → (cc)s transitions, and with the Standard Model expectation of small penguin contributions.

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