Evidence for a scalar glueball

Abstract

We show that the newly discovered scalar meson f 0 (1500) at LEAR has properties compatible with the lightest scalar glueball predicted by lattice QCD and incompatible with a QQ state. We suggest that decays of glueballs are into pairs of glueballs (including η, η ′ or (ππ) S ) or by mixing with nearby QQ states. The partial widths of f 0 (1500) are in accord with this hypothesis, tests of which include characteristic radiative decays to γφ, γω, γρ and the prediction of a further scalar state, f ′ 0 (1500 − 1800) which couples strongly to KK, ηη and ηη ′ .

Towards resolution of the scalar meson nonet enigma

“…For the a 0 (980) taken as the isovector scalar state, our solution exhibits a number of interesting features: It predicts an f 0 -f ′ 0 mixing angle close to the ideal mixture value (8), i.e., both isoscalar states would be almost pure nn and ss; their masses are predicted to be in agreement with those of the σ of the most recent edition of PDG and the f J (1710), respectively. The existence of the latter state, which in this case is almost pure ss, would be in agreement with the prediction by Amsler and Close [15]. However, we will disregard this solution as unphysical.…”

“…This pattern can be reproduced by assuming the existence of an additional scalar state which is mainly ss and should have a mass of about 1700 MeV, possibly the f J (1710), and tuning the mixing of the f 0 (1500) with the f 0 (1370) nn (n = u, d) and the (predicted) f 0 (1700) ss states [15]. In this picture, the f 0 (1500) is interpreted as a glueball state with strong mixing with the close-by conventional scalar mesons.…”

“…It was claimed that this state has a peculiar decay pattern 1 [15] ππ : ηη : ηη ′ : KK = 1.45 : 0.39 ± 0.15 : 0.28 ± 0.12 :< 0.15.…”

Structure of $f_0(980)$ from a coupled channel analysis of $S$ -wave $\pi\pi$ scattering

“…In our model this resonance is needed to describe the rise of the ππ scattering phase above the KK threshold. It can be considered as an approximation for the higher resonances, in particular, the f 0 (1300), and our results for the remote poles s II D and s III E should be considered as an estimate rather than the parameters of real physical structures (for the discussion of this energy region see [3,4,5,41,17,43] and references therein).…”

“…Recently this problem attracted new attention after a candidate for the scalar glueball was found at LEAR [2,3]. A characteristic feature of the J P C I G = 0 ++ 0 + channel is that the mixing between different states is strong, so that a connection between the observed resonances and bare states, like quarkonia or glueballs, is nontrivial [4,5].…”