$K_L \to \pi^0 e^+ e^-$ and $B \to X_s \ell^+ \ell^-$ Decay in the MSSM

Abstract

The flavor changing neutral current processes $K_L \to \pi^0 e^+ e^-$, $B \to X_s e^+ e^-$ and $B \to X_s \mu^+ \mu^-$ are studied within the minimal supersymmetric extension of the Standard Model. We first examine the rates for these decay modes in the MSSM with a universal soft supersymmetry breaking sector at a Grand Unification scale. We later relax the universality condition and investigate the FCNC transitions in a more general class of models with negligible flavor violation in squark mixing matrices. We find that the MSSM prediction for the kaon channel's branching fraction differs from its Standard Model value by at most 30\% over the entire allowed parameter space. On the other hand, supersymmetric contributions could potentially enhance certain $B \to X_s \ell^+ \ell^-$ observables by more than 100\% relative to Standard Model expectations. The impact of supersymmetry upon the $B$ meson modes is strongly correlated with the MSSM value for the Wilson coefficient of the magnetic moment operator that mediates $B \to X_s \gamma$.