B→Kη^(') decays in the SM with fourth generation fermions

Abstract：

By employing the perturbative QCD (pQCD) factorization approach, we calculate the new physics contributions to the four B→Kη^(') decays in the Standard Model (SM) with a fourth generation of fermions (SM4), induced by the loop diagrams involving t' quark. Within the considered parameter space of the SM4 we find that: (a) the next-to-leading order (NLO) pQCD predictions for the branching ratios and CP-violating asymmetries in both the SM and SM4 generally agree with the data within one standard deviation; (b) for Br( B→Kη), the inclusion of the fourth generation contributions can improve the agreement between the theoretical predictions and the data effectively; (c) however, for Br( B→Kη') the decrease due to t' loops is disfavored by the data; and, (d) the new physics corrections to the CP-violating asymmetries of the considered decays are only about 10%.