Identification of the glueballs and the scalar meson nonet of lowest mass

We discuss the theoretical expectations and phenomenological evidence for the lightest glueballs and the members of the meson nonet with quantum numbers JPC = 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 f0(980) and f0(1500) as members of the O++ nonet, with a mixing rather similar to that of the pseudoscalars η′ and η. The S-wave states called f0(400 - 1200) and f0(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 fJ(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.