Measuring sin 2 beta in B-s(0)(t) -> phi K-S

We show that, unlike other pure b --> d penguin processes, the decay B-s(0) (t) --> phiK(S) is dominated by a single amplitude, that of the internal t- quark. The contributions of the u- and c-quark operators each vanish due to a cancellation between the (V - A) circle times (V - A) and (V - A) circle times (V + A) matrix elements. Thus, the indirect CP asymmetry in this dec ay probes sin2 beta. Although this cancellation is complete only for certai n values of the s- and b-quark masses, the theoretical uncertainty on sin2 beta is still less than 10% over most (similar to 80%) of the parameter spa ce. By measuring the direct CP asymmetry, one can get a better idea of the probable error on sin2 beta. (C) 2001 Published by Elsevier Science B.V.