Aubert, B. et al. (2004) Measurement of the Time-Dependent CP Asymmetry in the B0→ϕK0 Decay. Physical Review Letters, 93 (7). 071801. ISSN 0031-9007

We present a measurement of the time-dependent CP asymmetry for the neutral B-meson decay B0→ϕK0. We use a sample of approximately 114×106 B-meson pairs taken at the Υ(4S) resonance with the BABAR detector at the PEP-II B-meson factory at SLAC. We reconstruct the CP eigenstates ϕKS0 and ϕKL0, where ϕ→K+K-, KS0→π+π-, and KL0 is observed via its hadronic interactions. The other B meson in the event is tagged as either a B0 or B̅ 0 from its decay products. The values of the CP-violation parameters are SϕK=0.47±0.34(stat)-0.06+0.08(syst) and CϕK=0.01±0.33(stat)±0.10(syst).