Comparative study of CP asymmetries in supersymmetric models

We systematically analyze the supersymmetric contributions to the mixing CP asymmetries and branching ratios of B --> phi K-S and B --> eta' K-S processes. We consider both gluino and chargino exchanges in a model independent way by using the mass insertion approximation method. While we adopt the QCD factorization approach for evaluating the corresponding hadronic matrix elements, a critical comparison with predictions in naive factorization one is also provided. We find that pure chargino contributions cannot accommodate the current experimental results on CP asymrnetries, mainly due to b --> sgamma constraints. We show that charged Higgs contributions can relax these constraints making chargino responsible for large asymmetries. On the other hand, pure gluino exchanges can easily saturate both the constraints on B --> phi K-S and B --> eta' K-S CP asymmetries. Moreover, we also find that the simultaneous contributions from gluino and chargino exchanges could easily account for the present experimental results on the mentioned asymmetries. Remarkably, large experimentally allowed enhancements of B --> eta' K-S branching ratio can easily be achieved by the contribution of two mass insertions in gluino exchanges. Finally, we analyze the correlations between the CP asymmetries of these processes and the direct CP asymmetry in b --> sgamma decay. When all experimental constraints are satisfied, supersymmetry favors large and positive values of b --> sgamma asymmetry. (C) 2005 Elsevier B.V. All rights reserved.