A study of the J/psi production in proton-proton collisions at the CERN ISR, using liquid argon calorimeters and lithium/xenon transition radiation detectors

The production of electron-positron (e+e-) pairs with invariant masses greater than 2.5 GeV/c2 was investigated at the CERN Intersecting Storage Rings. The J/psi particle was observed by its decay into e+e- pairs and its production cross-section is found to rise by a factor of about six over the entire range of centre-of-mass energies available (√s=23.5 GeV to √s=62.4 GeV). The rapidity and transverse momentum dependence of the production mechanism are discussed. The e+e- pair invariant mass spectrum is also studied for higher masses. The production and decay into e+e- pairs of the psi' is not observed within the statistical limits of the data discussed herein. A few e+e- events with masses above 4.5 GeV/c2 are observed and are used to set upper limits on the cross-section for continuum production resulting from the annihilation of elementary point-like constituents of the protons. (Auth.)