Search for B→K^{(*)}νν[over ̄] 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 471×106 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(B0→K0νν ̄)<8.1×10-5, B(B+→K*+νν ̄)<11.6×10-5, B(B0→K*0νν ̄)<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→νν ̄)<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.