Possible exotic mesons in the charmonium region

We consider the possibility that a number of PC=+ + mesons might appear in the charmonium region below (3.69 GeV). They are states made up of admixtures of ccg (g=gluon), ccqq (q=u,d), and the charmonium PJ3 states. Masses, decay widths, and mixing matrix elements are studied with the help of the model of Horn and Mandula for ccg states and the results of Jaffe, and De Rújula and Jaffe, for ccqq states. The presence of a cc pair suggests narrow hadronic widths if the mass is below the breakup thresholds of the ccqq states. Their branching ratios for transitions and 2 anmihilations appear to be fairly small. They may have rather large spin-spin splittings. It is plausible that the lowest-mass states contain mostly ccg configurations. Although they share part of the charmonium PJ3 -cascade strengths, it is likely that they are more readily produced in the hadronic decays of vector mesons in e+e- annihilations. We also discuss the possible appearance of similar states in the region and among light mesons. We suggest in particular that strange mesons in suitable decay modes might well provide the most ready experimental access to such gluon and four-quark states.