The cross-section for $J/\Psi$ production in proton-proton collisions at center-of-mass energies between 23 and 63 GeV

The cross-section for J/ psi production in proton-proton collisions has been measured as a function of centre-of-mass energy at the CERN Intersecting Storage Rings by observing its decay into electron- positron pairs. This cross-section is found to rise by a factor of about six over the full centre-of-mass energy range from square root s =23 to square root s=63 GeV. Electrons resulting from this decay were identified by the use of liquid argon calorimeters and lithium foil transition radiators. Measurements of the energies of the electrons were obtained from the liquid argon calorimeters. (4 refs).