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

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