CP violation in $B \to φK_S$ decay at large $\tanβ$

We consider the chargino contribution to the CP violation in $B \to \phi K_S$ decay in the minimal supersymmetric standard model at large $\tan\beta$. It is shown that the Wilson coefficient $C_{8g}$ of the chromomagnetic penguin operator can be significantly enhanced by the chargino-mediated diagrams while satisfying other direct/indirect experimental constraints. The enhanced $C_{8g}$ allows large deviation in the CP asymmetry from the standard model prediction, especially it can explain the apparent anomaly reported by BaBar and Belle.