A new measurement of the b ¯ b production cross section in 920 GeV proton-nucleus collisions is presented by the HERA-B Collaboration. The b ¯ b production is tagged via inclusive bottom quark decays into J / ψ mesons by exploiting the longitudinal separation of J / ψ → l + l − decay vertices from the primary proton-nucleus interaction point. Both e + e − and μ + μ − channels are reconstructed for a total of 83 ± 12 inclusive b → J / ψ X events found. The combined analysis yields a b ¯ b to prompt J / ψ cross section ratio of Δ σ ( b ¯ b ) Δ σ J / ψ = 0.032 ± 0.005 stat ± 0.004 sys measured in the x F acceptance ( − 0.35 < x F < 0.15 ), extrapolated to σ ( b ¯ b ) = 14.9 ± 2.2 stat ± 2.4 sys     nb/nucleon in the total phase space.