Measurement of the B-meson and b-quark cross sections at sqrt s =1.8 TeV using the exclusive decay B+/--->J/ psi K+/-

This Letter reports the full reconstruction of B mesons through the decay chain B ± →J/ψK ± , J/ψ→μ + μ - , using data obtained at the Collider Detector at Fermilab in pp 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 B - mesons with P T >9.0 GeV/c and rapidity |y| 11.5 GeV/c and rapidity |y|<1.0