Preliminary estimates suggest that excess dimuon production with invariant mass in the range 1.5 -- 2.5 GeV in nucleus-nucleus collisions can be explained on the basis of $eta_c$ production. This appears to be consistent with all the peripheral and central collision data with various nuclei such as S-U at 200 GeV/nucleon except for the central collision data on Pb-Pb at 158 GeV/nucleon. Some explanations based on glueball production for Pb-Pb data are discussed.
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