Which observed scalar mesons contain the lightest glueball?
In plain words
QCD predicts particles made only of gluons, called glueballs, with the lightest near 1.7 GeV. It mixes with ordinary quark-antiquark states, and which observed particles contain it is disputed.
Precise statement
Quenched lattice QCD places the $0++$ glueball near $1.7\,\mathrm{GeV}$. Among $f0(1370)$, $f0(1500)$, $f0(1710)$ and $f0(1770)$, determine the glueball content (mixing fractions with $n-\mathrm{nbar}$ and $s-\mathrm{sbar}$), using $J/\psi$ radiative decays, two-photon widths, decay branching ratios and lattice QCD with dynamical quarks. Answer: a mixing scheme consistent with all production and decay data.
What would settle it
Lattice QCD scattering calculation of the isoscalar scalar channel with glueball operators at physical quark masses, combined with coupled-channel fits to BESIII and LHCb data.
Status in the literature
Unverified note
Coupled-channel analyses of BESIII radiative $J/\psi$ decay data (around 2021-2022) assigned the largest glueball fraction to states near $1.7\ \text{to}\ 1.9\,\mathrm{GeV}$, with amplitude-model dependence unresolved as of 2026.