Searches for B0 Decays to Combinations of Two Charmless Isoscalar Mesons

We search for B meson decays into two-body combinations of η,η′,ω, and ϕ mesons from 89×106 BB̅ pairs collected with the BABAR detector at the PEP-II asymmetric-energy e+e- collider at SLAC. We find the branching fraction B(B0→ηω)=(4.0-1.2+1.3±0.4)×10-6 with a significance of 4.3σ. For the other decay modes we set the following 90% confidence level upper limits on the branching fractions, in units of 10-6: B(B0→ηη)<2.8, B(B0→ηη′)<4.6, B(B0→η′η′)<10, B(B0→η′ω)<2.8, B(B0→ηϕ)<1.0, B(B0→η′ϕ)<4.5, and B(B0→ϕϕ)<1.5.