Inclusive J/ψ and ψ′ production in π−-nucleus interactions at √s ⋍ 26 GeV

Abstract Charmonium production by 350 GeV/ c negative pions incident on tungsten, copper and silicon has been studied in the WA92 experiment. J / ψ and ψ′ mesons are identified through their decays into muon pairs and are selected in the Feynman-χ range χ F > 0. Inclusive J / ψ and ψ′ cross-sections and J / ψ differential cross-sections as functions of χ F and p T 2 are measured. Assuming the relation σ = σ 0 A α between the nuclear cross-section, σ, and the atomic mass, A , of a target nucleus, a fit to J / ψ data for different targets yields α = 0.87 ± 0.05 ± 0.04. Taking α = 0.87, the cross-sections per nucleon for J / ψ and ψ′ are σ 0 ( J / ψ ) = 216 ± 5 ± 13 nb and σ 0 ( ψ ′) = 28 ± 8 ± 11 nb, and their ratio is σ 0 ( ψ ′)/ σ 0 ( J / ψ ) = 0.13 ± 0.05 ± 0.01. The measurements of charmonium production are compared with results on open-charm production previously obtained in the same experiment. The ratio between the J / ψ cross-section and the charmed-meson cross-section, relating to the same experimental conditions, is found to be σ 0 (J/ψ)/σ 0 (D D − ) = 1.75±0.05±0.15) × 10 −2 .