Calculation of magnetic penguin amplitudes in B → φK decays using PQCD approach

New physics contributions to B decays often arise through chromo-magnetic penguin operators. To look for new physics effects in B decays, it is useful to be able to estimate the hadronic matrix elements for the chromo-magnetic operator. We compute this contribution to B --> phiK decays using PQCD methods. It is shown that, if the Wilson coefficient of the new physics is same order of magnitude as that of the Standard Model, this operator gives a non-negligible contribution compared to that of the Standard Model (about 30%). We also investigate the value of q(2) which is the momentum transferred by the gluon in the chromo-magnetic penguin operator. We find that the expectation value is approximately M-B(2)/4, in agreement with a naive. This result, however, is very sensitive to the scale dependence of the Wilson coefficient. We also show that the matrix element for the chromomagnetic penguin operator is independent of the choice of energy scale to a very good approximation.