title: Effect of penguin operators in the B0 --> J/psiK0 CP asymmetry.
abstract: Performing a fit to the available experimental data, we quantify the effect of long-distance contributions from penguin contractions in B0 --> J/psiK0 decays. We estimate the deviation of the measured S(CP) term of the time-dependent CP asymmetry from sin2beta induced by these contributions and by the penguin operators. We find deltaS is identically equal to S(CP)(J/psiK) - sin2beta = 0.000 +/- 0.012 ([-0.025, 0.024]@95% probability), an uncertainty much larger than previous estimates and comparable to the present systematic error quoted by the experiments at the B factories.
authors.affiliation: Dipartimento di Fisica, Università La Sapienza and INFN, Sezione di Roma, P.le A. Moro, I-00185 Rome, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Ciuchini
authors.forename: M
authors.initials: M
authors.lastname: Pierini
authors.forename: L
authors.initials: L
authors.lastname: Silvestrini