Search

Measurements of the kinematic distributions of J/ ψ mesons produced in p–C, p–Ti and p–W collisions at $\sqrt{s}=41.6~\mathrm{GeV}$ in the Feynman- x region −0.34< x F<0.14 and for transverse momentum up to p T=5.4 GeV/c are presented. The x F and p T dependencies of the nuclear suppression parameter, α, are also given. The results are based on 2.4×105 J/ ψ mesons reconstructed in both the e+ e− and μ+ μ− decay channels. The data have been collected by the HERA-B experiment at the HERA proton ring of the DESY laboratory. The measurement explores the negative region of x F for the first time. The average value of α in the measured x F region is 0.981±0.015. The data suggest that the strong nuclear suppression of J/ ψ production previously observed at high x F turns into an enhancement at negative x F. [ABSTRACT FROM AUTHOR]

Ratios of the ψ′ over the J/ψ production cross sections in the dilepton channel for C, Ti and W targets have been measured in 920 GeV proton-nucleus interactions with the HERA-B detector at the HERA storage ring. The ψ′ and J/ψ states were reconstructed in both the μ+μ- and the e+e- decay modes. The measurements covered the kinematic range -0.35≤xF≤0.1 with transverse momentum pT≤4.5 GeV/ c. The angular dependence of the ratio has been used to measure the difference of the ψ′ and J/ψ polarization. All results for the muon and electron decay channels are in good agreement: their ratio, averaged over all events, is Rψ′(μ)/Rψ′(e)=1.00±0.08±0.04. This result constitutes a new, direct experimental constraint on the double ratio of branching fractions, (B′(μ)B(e))/(B(μ)B′(e)), of ψ′ and J/ψ in the two channels. The ψ′ to J/ψ production ratio is almost constant in the covered xF range and shows a slow increase with pT. [ABSTRACT FROM AUTHOR]

Using the HERA - B detector, the bb production cross section has been measured in 920 GeV proton collisions on carbon and titanium targets. The bb production was tagged via inclusive bottom quark decays into J/ψ by exploiting the longitudinal separation of J/ψ → l+l- decay vertices from the primary proton-nucleus interaction. Both e+e- and u+u- channels have been reconstructed and the combined analysis yields the cross section σ(bb) 32-12+14(stat)-7+6(sys) nb/nucleon. [ABSTRACT FROM AUTHOR]

Abstract: The production cross section in 920 GeV proton-nucleus fixed target collisions is measured by observing double muonic decays of b-flavoured hadrons in the kinematic region . A total number of events is obtained with a likelihood fit of the signal and background simulated events to the data. The resulting cross section is , or, when combined with a previous HERA-B measurement of similar precision, , which is consistent with recent NLO calculations. [Copyright &y& Elsevier]

Abstract: The cross section ratio has been measured with the HERA-B spectrometer in fixed-target proton–nucleus collisions at 920 GeV proton beam energy corresponding to a proton–nucleon c.m.s. energy of . The combined results for the decay channels and yield a ratio . The corresponding ϒ production cross section per nucleon at mid-rapidity () has been determined to be . [Copyright &y& Elsevier]