We discuss the theoretical expectations and phenomenological evidence for the lightest glueballs and the members of the meson nonet with quantum numbers J P C = 0 ++ . We reconsider the recent evidence for candidate states with masses below ∼1700 MeV, but include also the results from earlier phase-shift analyses. Arguments are presented to classify the scalars f 0 (980) and f 0 (1500) as members of the 0 ++ nonet, with a mixing rather similar to that of the pseudoscalars η and η. The S-wave states called f 0 (400 − 1200) and f 0 (1370) are considered as different signals from a single broad resonance, which we take to be the lowest-lying 0 ++ glueball. This state together with η(1440) and f J (1710) with spin J = 2 form the basic triplet of binary gluonic bound states. We argue that these hypotheses are consistent with what can be expected theoretically.
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