First Measurement of the CP -Violating Asymmetries with BABAR

We report on a preliminary measurement of time-dependent CP -violating asymmetries in B ! J= K S and B ! (2S)K S decays recorded by the BABAR detector at the PEP-II asymmetric B Factory at SLAC. The data sample consisted of 9.0 fb 1 collected at the (4S) resonance and 0.8 fb 1 o -resonance. One of the pair of neutral B mesons produced at the (4S) was fully reconstructed, while the avor of the other neutral B meson was tagged at the time of its decay. The value of the asymmetry amplitude, sin2 , was determined from a maximum likelihood t to the time distribution of 120 tagged candidates to be sin2 = 0:12 0:37(stat:) 0:09(syst:) (preliminary). Contributed to the Proceedings of the DPF2000 Meeting of the Division of Particles and Fields of the American Physics Society, 8/9/2000|8/12/2000, Columbus, OH Stanford Linear Accelerator Center, Stanford University, Stanford, CA 94309 Work supported in part by Department of Energy contract DE-AC03-76SF00515.