Inclusive J/psi and psi' production in pi sup - -nucleus interactions at sq root s approx = 26 GeV

Charmonium production by 350 GeV/c negative pions incident on tungsten, copper and silicon has been studied in the WA92 experiment. J/psi and psi' mesons are identified through their decays into muon pairs and are selected in the Feynman-chi range chi sub F > 0. Inclusive J/psi and psi' cross-sections and J/psi differential cross-sections as functions of chi sub F and p sub T sup 2 are measured. Assuming the relation sigma sigma sub 0 A supalpha between the nuclear cross-section, sigma, and the atomic mass, A, of a target nucleus, a fit to J/psi data for different targets yields alpha = 0.87 +- 0.05 +- 0.04. Taking alpha = 0.87, the cross-sections per nucleon for J/psi and psi' are sigma sub 0 (J/psi) 216 +- 5 +- 13 nb and sigma sub 0 (psi') = 28 +- 8 +- 11 nb, and their ratio is sigma sub 0 (psi')/sigma sub 0 (J/psi) = 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/psi cross-section and the charmed-meson cross-section, relating to the same experimental conditions, is found to be sigma sub 0 (J/psi)/sigma sub 0 (DD-) = 1.75+-0.05+-0.15) x 10 sup - sup 2