The Fragmented Glueball: A Personal View

TL;DR

This paper performs a comprehensive coupled-channel analysis of scalar mesons, revealing ten isoscalar resonances, their SU(3) classifications, and evidence for the lightest scalar glueball through radiative $J/ar{p}$ decays.

Contribution

It introduces a detailed coupled-channel analysis combining diverse experimental data to identify scalar meson resonances and their SU(3) properties, providing evidence for the scalar glueball.

Findings

Ten scalar isoscalar resonances identified.

Resonances classified into SU(3) singlet and octet groups.

Evidence for the lowest-mass scalar glueball in radiative decays.

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 $\pi^0\pi^0$,$K_SK_S$, $\eta\eta$, and $\omega\phi$, 15 Dalitz plots from $\bar pN$ 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 $K_SK_S$, from GAMS data on $\pi\pi\to \pi^0\pi^0, \eta\eta$, and $\eta\eta'$, 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.