The Gold-plated mode revisited: sin(2 beta) and B⁰ to J/Psi K_S in the Standard Model

We study the corrections to the determination of sin(2 beta) from the time dependent CP asymmetry of B^0 to J/Psi K_S which arise in the standard model. Although a precise prediction of these corrections is not possible we find that they are indeed extremely small, of the order of less than a per mil of the observed value. This means in turn that any deviation visible at the B factories will be a clear signal for new physics.