Time-integrated and time-dependent angular analyses of B ! J= K(cid:6) : A measurement of cos2 (cid:7) with no sign ambiguity from strong phases

We present results on B ! J= K(cid:6) decays using e (cid:2) e (cid:3) annihilation data collected with the BABAR detector at the (cid:2) (cid:4) 4 S (cid:5) resonance. The detector is located at the PEP-II asymmetric-energy storage ring facility at the Stanford Linear Accelerator Center. Using approximately 88 (cid:6) 10 6 BB pairs, we measure the decay amplitudes for the flavor eigenmodes and observe strong-phase differences indicative of final-*Also state interactions with a significance of 7.6 standard deviations. We use the interference between the K(cid:6) S -wave and P -wave amplitudes in the region of the K (cid:7) (cid:4) 892 (cid:5) to resolve the ambiguity in the determination of these strong phases. We then perform an ambiguity-free measurement of cos2 (cid:10) using the angular and time-dependent asymmetry in B ! J= K (cid:7) 0 (cid:4) K 0 S (cid:6) 0 (cid:5) decays. With sin2 (cid:10) fixed at its measured value and cos2 (cid:10) treated as an independent parameter, we find cos2 (cid:10) (cid:8) 2 : 72 (cid:2) 0 : 50 (cid:3) 0 : 79 (cid:4) stat (cid:5) (cid:9) 0 : 27 (cid:4) syst (cid:5) , determining the sign of cos2 (cid:10) to be positive at 86% C.L.