Charmonia production in 450 GeV/c proton induced reactions

Absolute J/psi and psi' production cross sections have been measured at the CERN SPS, with 450 GeV/c protons incident on a set of C. Al, Cu and W targets. Complementing these values with the results obtained by experiment NA51, which used the same beam and detector with H and D targets, we establish a coherent picture of charmonia production in proton-induced reactions at SPS energies. In particular, we show that the scaling of the J/psi cross section with the mass number of the target, A, is well described as A(alpha), with alpha(psi) = 0.919 +/- 0.015. The ratio between the J/psi and psi' yields, in our kinematical window, is found to be independent of A, with alpha(psi) - alpha(psi) = 0.014 +/- 0.011. (C) 1998 Elsevier Science B.V. All rights reserved.