MASS CORRECTIONS TO FORBIDDEN CHARMONIUM DECAYS - ETA-C,CHI-C0-]P(P)OVER-BAR

Some exclusive decays of charmonium states are forbidden, in the framework of perturbative QCD quark models, by the helicity-conservation rule, related to the vector coupling of gluons to (almost) massless quarks. Among them, we consider here eta(c) and chi(c0) decays into ppBAR, after discussing possible nonperturbative corrections, we show that, assigning to the quarks a constituent rather than a current mass, one obtains nonzero values for such processes. The values found for GAMMA(chi(c0)-->ppBAR) are almost as large as those obtained for similar, nonforbidden decays in the massless quark scheme, chi(c1,c2)-->ppBAR GAMMA(eta(c)-->ppBAR), however, turns out to be much smaller than the experimental data, enhancing, once more, the peculiarity of many eta(c), decays. Mass corrections to some other allowed decays, chi(c0)-->pipi and chi(c0) into longitudinally polarized vector mesons, are computed and shown to be relevant.