0 + mesons

Abstract

The status of 0 + mesons is reviewed. A ground-state nonet may be identified, consisting of f 0(1335), a 0(1450) and K ∗(1430) . An additional state f 0(1505), first observed in the Crystal Barrel experiment, makes an excellent candidate for the 0 + ground-state glueball. It is observed in ππ, ηη and ηη′. In J Ψ radiative decays, it is observed in σσ, where σ stands for the ππ S-wave. These data on J Ψ → γ(4π) also contain two further peaks due to f 0(1750) and f 0(2104), again decaying dominantly to σσ. Of these, f 0(2104) may be interpreted as a second 0 + glueball. The f 0(1505) and f 0(2104) appear strongly in the ηη channel in Crystal Barrel data in flight on pp → (ηη)π 0 , but 0(1750) does not. The natural explanation of f 0(1750) is a qq radial excitation, mixed with some gg component. The vital outstanding problem is to locate the s s member of the ground-state nonet.