Glueballs as the Ithaca of meson spectroscopy

Abstract

This compact review about gluonium focuses on a slate of theoretical efforts; among the many standing works, I have selected several that are meant to assist in the identification, among ordinary mesons, of the few Yang-Mills glueball configurations that populate the energy region below 3 GeV. This includes J/ψ radiative and vectormeson decays, studies of scalar meson mixing, of high-energy cross sections via the Pomeron and the odderon, glueball decays, etc. The weight of accumulated evidence seems to support the f0(1710) as having a large (and the largest) glueball component among the scalars, although no single observable by itself is conclusive. Further tests would be welcome, such as exclusive fJ production at asymptotically high s and t. No clear experimental candidates for the pseudoscalar or tensor glueball stand out yet, and continuing investigations trying to sort them out will certainly teach us much more about mesons.

Scalar and tensor resonances in $$J/\psi $$ radiative decays

“…In QCD, the mixing between glueballs and q q isoscalar mesons makes the identification of a glueball candidate challenging, both theoretically and experimentally. The simplest argument for the existence of a glueball component is the presence of a supernumerary state with respect to how many are predicted by the quark model [10][11][12]. It is thus of key importance to have a precise determination of the number and properties of the resonances seen in data.…”

Snowmass white paper: Need for amplitude analysis in the discovery of new hadrons

“…There are several interesting topics in the light sector. The most fundamental questions concern the existence of resonances where gluons play the role of constituents, as glueball or hybrid mesons [19][20][21]. The isoscalar-scalar mesons, and -tensor mesons to some extent, have played a central role in this.…”

Novel approaches in Hadron Spectroscopy

“…There are several interesting topics in the light sector. The most fundamental questions concern the existence of resonances where gluons play the role of constituents, as glueball or hybrid mesons [145][146][147]. The analysis of isoscalar scalar and tensor mesons in the 1-2.5 GeV region-where the lightest glueball is expected-is presented in Section 2.4.1.…”

“…Most of the literature traces the existence of a significant glueball component with the emergence of a supernumerary state with respect to how many are predicted by the quark model [145,146,163]. The PDG lists seven inelastic scalar-isoscalars, in particular the f 0 (1370), f 0 (1500), f 0 (1710) in the 1.2-2 GeV are one more than expected by the quark model, which stimulated an intense work to identify one of them as the glueball [164][165][166][167][168][169][170][171].…”