The Fragmented Glueball: A Personal View

Abstract

A coupled-channel analysis has been performed to identify the spectrum of scalar mesons. The data include BESIII data on radiative $J/\psi$ decays into ${\pi }^0{\pi }^0$,$K_S{K}_S$, $\eta \eta$, and $\omega \varphi$, 15 Dalitz plots from $\bar{p}N$ annihilation at rest at LEAR, the CERN-Munich multipoles for $\pi \pi$ elastic scattering, the $S$-wave from BNL data on $\pi \pi$ scattering into $K_S{K}_S$, from GAMS data on $\pi \pi \to {\pi }^0{\pi }^0,\eta \eta$, and $\eta {\eta }^{\prime }$, and NA48/2 data on low-mass $\pi \pi$ interactions from $K^{\pm }\to \pi \pi e^{\pm }\nu$ decays. The analysis reveals the existence of ten scalar isoscalar resonances. The resonances can be grouped into two classes: resonances with a large SU(3) singlet component and those with a large octet component. The production of isoscalar resonances with a large octet component should be suppressed in radiative $J/\psi$ decays. However, in a limited mass range centered at 1900\,MeV, these mesons are produced abundantly. Mainly-singlet scalar resonances are produced over the full mass range but with larger intensity at 1900\,MeV. The total scalar isoscalar yield in radiative decays into scalar mesons shows a clear peak which is interpreted as the scalar glueball of lowest mass.

Contribution to Quark Confinement and the Hadron Spectrum 2021. 6 pages, 5 figures, 2 tables

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