Improved measurement of the bb̄ production cross section in 920 GeV fixed-target proton-nucleus collisions

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