Measurement of open beauty production at HERA

The first observation of open b production in ep collisions is reported. An event sample containing muons and jets has been selected which is enriched in semileptonic b quark decays. The visible cross section sigma(ep --> b (b) over bar X --> mu X') for Q(2) < 1 GeV2, 0.1 < y < 0.8 is measured to be 0.176 +/- 0.016(stat.)(+0.026)(-0.017)(syst.) nb for the muons to be detected in the range 35 degrees < theta(mu) < 130 degrees and p(perpendicular to)(mu) > 2.0GeV in the laboratory frame. The expected visible cross section based on a NLO QCD calculation is 0.104 +/- 0.017nb. The cross sections for electroproduction with Q(2) < 1GeV(2) and photoproduction are derived from the data and found to be sigma(ep --> eb (b) over bar X) = 7.1 +/- 0.6(stat.)(-1.3)(+1.5)(syst.)nb and sigma(gamma p --> b (b) over bar X) = 111+/- 10(stat.)(-20)(+23) (syst.) nb at an average [W-gamma p] similar to 180GeV, respectively. (C) 1999 Published by Elsevier Science B.V. All rights reserved.