  Using the HERA-B detector, the b-bbar production cross section has been
measured in 920 GeV proton collisions on carbon and titanium targets. The
b-bbar production was tagged via inclusive bottom quark decays into J/psi, by
exploiting the longitudinal separation of J/psi->ll decay vertices from the
primary proton-nucleus interaction. Both $e^+e^-$ and $\mu^+\mu^-$ channels
have been reconstructed and the combined analysis yields the cross section
$\sigma(b \bar b) = 32 ^{+14}_{-12} (stat) ^{+6}_{-7} (sys) nb/nucleon$.
