Gluonium nature of the σ/f0(600) from its coupling to KK¯

We extract the K+K− couplings of the isoscalar scalar mesons σ/f0(600) and f0(980) from ππ→ππ/KK¯ scatterings. We find respectively about 0.6(2) and 2.0(3) for the ratios of the K+K− over π+π− couplings of the σ and f0(980), which we compare with some other determinations. The (relative) strong coupling of the σ→K¯K, together with its tiny “direct” γγ and its large hadronic widths, are in favour of a large gluonium/glueball component of the σ-meson, as predicted by QCD spectral sum rules (QSSR) ⊕ some low-energy theorems (LET). These properties then suggest that the σ can be (up to some mixing) a scalar meson associated to the U(1)V conformal anomaly like the η′-meson to the U(1)A anomaly.