Measurement of the bottom-quark production cross section in 800 GeV/c proton-gold collisions.

Using a silicon-microstrip detector array to identify secondary vertices, we have observed {ital b}{r_arrow}{ital J}/{psi}{r_arrow}{mu}{sup +}{mu}{sup {minus}} decays in 800 GeV/{ital c} proton-gold interactions. The doubly differential cross section for {ital J}/{psi} mesons originating from {ital b}-quark decays, assuming linear dependence on nucleon number, is {ital d}{sup 2}{sigma}/{ital dx}{sub {ital Fdp}}{sup 2}{sub {ital T}}=107{plus_minus}28{plus_minus}19/nucleon at {ital x}{sub {ital F}}=0.05 and {ital p}{sub {ital T}}=1GeV/{ital c}. This measurement is compared to next-to-leading-order QCD predictions. The integrated {ital b}-quark production cross section, obtained by extrapolation over all {ital x}{sub {ital F}} and {ital p}{sub {ital T}}, is {sigma}({ital pN}{r_arrow}{ital bb}{ovr bar}+{ital X})=5.7{plus_minus}1.5{plus_minus}1.3 nb/nucleon.