Bottom production cross section from double muonic decays of b-hadrons in 920 GeV proton-nucleus collision

The b-bbar production cross section in 920 GeV proton-nucleus fixed target collisions is measured by observing double muonic decays of b-flavored hadrons in the kinematic region $-0.3<\xF(\mu)<0.15$. A total number of $76\pm12$ b-bbar events is obtained with a likelihood fit of the signal and background simulated events to the data. The resulting cross section is $\sigbb = 16.2 \pm 2.5_{stat} \pm 2.8_{sys} \nbpn$, or, when combined with a previous Hera-B measurement of similar precision, $\sigbb = 15.4 \pm 1.7_{stat} \pm 1.2_{sys}^{uncorr.} \pm 1.9_{sys}^{corr.} \nbpn$, which is consistent with recent NLO calculations.