Measurement of CP asymmetries in B0→ϕK0 and B0→K+K-Ks0 decays

We measure the time-dependent CP asymmetry parameters in B0→K+K-K0 based on a data sample of approximately 227×10^6 B-meson pairs recorded at the Υ(4S) resonance with the BABAR detector at the PEP-II B-meson Factory at SLAC. We reconstruct two-body B0 decays to ϕ(1020)KS0 and ϕ(1020)KL0, and the three-body decay K+K-KS0 with ϕ(1020)KS0 excluded. For the B0→ϕK0 decays, we measure sin⁡2βeff(ϕK0)=+0.50±0.25(stat)-0.04+0.07(syst). The B0→K+K-KS0 decays are dominated by K+K- S wave, as determined from an angular analysis; we measure sin⁡2βeff(K+K-KS0)=+0.55±0.22(stat)±0.04(syst)±0.11(CP), where the last error is due to the uncertainty in the fraction of CP-even contributions to the decay amplitude. We find no evidence for direct CP violation.