Open and Hidden Beauty Production in 920 GeV Proton-Nucleus Collisions

HERA‐B is a fixed‐target multi‐particle spectrometer experiment at the 920 GeV HERA proton beam at DESY. Approximately 150 million events were recorded with a dilepton trigger during the 2002/2003 HERA run. About 300,000 leptonic J/ψ decays (170,000 in the dimuon channel and 130,000 in the dielectron channel) have been reconstructed in this data sample. This statistics allows a new measurement of the bb̄ and of the Υ production cross sections. The b events have been tagged via inclusive bottom quark decays into a J/ψ, by exploiting the longitudinal separation of J/ψ → l+l− decay vertices from the primary proton‐nucleus interaction. The Υ cross section is measured in dimuon and dielectron decay channels.