Measurement of theB-meson andb-quark cross sections at √s=1.8 TeV using the exclusive decayB±→J/ψK±

This letter reports the full reconstruction of B mesons through the decay chain ${\mathit{B}}^{\pm }$→J/ψ ${\mathit{K}}^{\pm }$, J/ψ→${\mathrm{\mu }}^{+}$ ${\mathrm{\mu }}^{\mathrm{-}}$, using data obtained at the Collider Detector at Fermilab in p¯p collisions at √s =1.8 TeV. This exclusive sample, the first observed at a hadron collider, is then used to measure the B-meson cross section, from which we extract the b-quark cross section. We obtain σ=2.8±0.9 (stat) ±1.1(syst) μb for ${\mathit{B}}^{\mathrm{-}}$ mesons with ${\mathit{P}}_{\mathit{T}}$>9.0 GeV/c and rapidity ‖y‖11.5 GeV/c and rapidity ‖y‖<1.0.