Search for B→K(*)νν¯ and invisible quarkonium decays

We search for the flavor-changing neutral-current decays B→K^(*)νν, and the invisible decays J/ψ→νν and ψ(2S)→νν via B→K^(*)J/ψ and B→K^(*)ψ(2S), respectively, using a data sample of 471×10^6 BB pairs collected by the BABAR experiment. We fully reconstruct the hadronic decay of one of the B mesons in the Υ(4S)→BB decay, and search for the B→K^(*)νν decay in the rest of the event. We observe no significant excess of signal decays over background and report branching fraction upper limits of B(B^+→K^+νν)<3.7×10^(-5), B(B^0→K^0νν)<8.1×10^(-5), B(B^+→K^(*+)νν)<11.6×10^(-5), B(B^0→K^(*0)νν)<9.3×10^(-5), and combined upper limits of B(B→Kνν)<3.2×10-5 and B(B→K^*νν)<7.9×10^(-5), all at the 90% confidence level. For the invisible quarkonium decays, we report branching fraction upper limits of B(J/ψ→νv)<3.9×10^(-3) and B(ψ(2S)→νν)<15.5×10^(-3) at the 90% confidence level. Using the improved kinematic resolution achieved from hadronic reconstruction, we also provide partial branching fraction limits for the B→K^(*)νν decays over the full kinematic spectrum.