Penguin pollution in theB0→J/ψKSdecay

We present the most complete analysis of the penguin correction to theextraction of the standard-model parameter sin(2\phi_1) from the B^0 -> J/psiK_S decay up to leading power in 1/m_b and to next-to-leading order in\alpha_s, \phi_1 being the weak phase, m_b the b quark mass, and \alpha_s thestrong coupling constant. The deviation \Delta S_{J/psi K_S} of themixing-induced CP asymmetry from sin(2\phi_1) and the direct CP asymmetryA_{J/psi K_S} are both found to be of O(10^{-3}) in a formalism that combinesthe QCD-improved factorization and perturbative QCD approaches. The aboveresults, different from those of O(10^{-4}) and of O(10^{-2}) obtained in theprevious calculations, provide an important standard-model reference forverifying new physics from the B^0 -> J/psi K_S data.Comment: 6 pages, REVTeX4; minor corrections, version to appear in JHE