Gluonium nature of the sigma/f_0(600) from its coupling to KK

TL;DR

This paper investigates the nature of the sigma/f_0(600) meson, providing evidence from coupling ratios and decay widths that support its interpretation as a gluonium or glueball state, aligning with QCD predictions.

Contribution

The study offers new coupling ratio measurements and interprets them as strong evidence for the gluonium nature of the sigma meson, contrasting with other models.

Findings

Coupling ratio |g_{sigma K+K-}|/|g_{sigma pi+pi-}|= 0.8

Coupling ratio |g_{f_0 K+K-}|/|g_{f_0 pi+pi-}|= 1.7

Sigma's properties suggest a gluonium/glueball identity.

Abstract

We extract the K+K- couplings of the isoscalar scalar mesons sigma/f_0(600) and f_0(980) from pi pi to pi pi / K K scatterings and found: |g_{sigma K+K-}|/ |g_{sigma pi+pi-}|= 0.8 and |g_{f_0 K+K-}|/ |g_{f_0 pi+pi-}|= 1.7. These results, together with the tiny "direct" gamma gamma width of the sigma and its large hadronic width, are a strong indication for the gluonium/glueball nature of the sigma-meson, as predicted by QCD spectral sum rules (QSSR) + some low-energy theorems (LET), while some other assignements (pi pi molecule, tetraquark state and ordinary qq meson) do not satisfy simultaneously these requirements from the data. These properties suggest that the sigma can be a scalar meson associated to the U(1)V conformal anomaly like is the eta'-meson for the U(1)A anomaly.