Corrections to Fermiʹs Golden Rule in φ→KK̄ decays

We analyze the decays φ→KK̄ utilizing a formulation of transition rates which explicitly exhibits corrections to Fermiʹs Golden Rule. These corrections arise in systems in which the phase space and/or matrix element varies rapidly with energy, as happens in φ→KK̄, which is just above threshold. We show that the theoretical corrections resolve a puzzling 5σ discrepancy between theory and experiment for the branching ratio R=Γ(φ→K+K−)/Γ(φ→K0K̄ 0).