ISSN - 15507998, Physical Review D - Particles, Fields, Gravitation and Cosmology, 2004, vol. 71, p. 032005-1
Time-integrated and time-dependent angular analyses of B → J/ψKπ: A measurement of cos2β with no sign ambiguity from strong phases
We present results on B → J/ψKπ decays using e<sup>+</sup> e<sup>-</sup> annihilation data collected with the BABAR detector at the Y(4S) resonance. The detector is located at the PEP-II asymmetric-energy storage ring facility at the Stanford Linear Accelerator Center. Using approximately 88 × 10<sup>6</sup> BB̄ pairs, we measure the decay amplitudes for the flavor eigenmodes and observe strong-phase differences indicative of final-state interactions with a significance of 7.6 standard deviations. We use the interference between the Kπ S-wave and P-wave amplitudes in the region of the K*(892) to resolve the ambiguity in the determination of these strong phases. We then perform an ambiguity-free measurement of cos2β using the angular and time-dependent asymmetry in B → J/ψK* <sup>0</sup>(K<inf>S</inf><sup>0</sup>π<sup>0</sup>) decays. With sin2β fixed at its measured value and cos2β treated as an independent parameter, we find cos2β = 2.72<inf>-0.79</inf><sup>+0.50</sup>(stat) ± 0.27(syst), determining the sign of cos2β to be positive at 86% C.L. © 2005 The American Physical Society.