Improved measurement of the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>b</mml:mi><mml:mover accent="true"><mml:mi>b</mml:mi><mml:mo>¯</mml:mo></mml:mover></mml:math>production cross section in 920 GeV fixed-target proton-nucleus collisions

A new measurement of the $b\overline{b}$ production cross section in 920 GeV proton-nucleus collisions is presented by the HERA-B Collaboration. The $b\overline{b}$ production is tagged via inclusive bottom quark decays into $J/\ensuremath{\psi}$ mesons by exploiting the longitudinal separation of $J/\ensuremath{\psi}\ensuremath{\rightarrow}{l}^{+}{l}^{\ensuremath{-}}$ decay vertices from the primary proton-nucleus interaction point. Both ${e}^{+}{e}^{\ensuremath{-}}$ and ${\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ channels are reconstructed for a total of $83\ifmmode\pm\else\textpm\fi{}12$ inclusive $b\ensuremath{\rightarrow}J/\ensuremath{\psi}X$ events found. The combined analysis yields a $b\overline{b}$ to prompt $J/\ensuremath{\psi}$ cross section ratio of $\frac{\ensuremath{\Delta}\ensuremath{\sigma}(b\overline{b})}{\ensuremath{\Delta}{\ensuremath{\sigma}}_{J/\ensuremath{\psi}}}=0.032\ifmmode\pm\else\textpm\fi{}{0.005}_{\mathrm{stat}}\ifmmode\pm\else\textpm\fi{}{0.004}_{\mathrm{sys}}$ measured in the ${x}_{F}$ acceptance ($\ensuremath{-}0.35&lt;{x}_{F}&lt;0.15$), extrapolated to $\ensuremath{\sigma}(b\overline{b})=14.9\ifmmode\pm\else\textpm\fi{}{2.2}_{\mathrm{stat}}\ifmmode\pm\else\textpm\fi{}{2.4}_{\mathrm{sys}}\text{ }\text{ }\mathrm{\text{nb/nucleon}}$ in the total phase space.