CMD-2 and SND results on the ρ, ω and ϕ

QCD tests of the puzzling scalar mesons

“…• A QSSR analysis of the four-quark assignement [35] of these states gives predictions which reproduce the experimental mass of the a 0 (980) [36,30,13], like do the lattice calculations [37]. The result for the hadronic coupling g a0K + K − in the four-quark scenario depends crucially on the operators describing the a 0 and can range from 1.6 GeV [38] to (5)(6)(7)(8) GeV [30]. However, the prediction for the ηπ can agree with the data [30] depending on the size of the operator mixing parameter.…”

“…Experimentally, there are well established scalar mesons with isospin I = 1, the a 0 (980), a 0 (1450) with isospin I = 1/2, the K * 0 (1410) meson, and with isospin I = 0, the f 0 -mesons at 980, 1370 [1,2] and 1500 MeV from GAMS, CRYSTAL BAR-REL [1,2], WA102 [3] and BES [4]. Besides these resonances, there are different experimental indications [2], especially from BES [4], E791 [5], FOCUS [6], KLOE [7], SND [8], CMD2 [9], BELLE [10], WA102 [3] and ππ scattering data [11,12] for some other scalar states, with I = 0, the σ(600), f 0 (1710) and f 0 (1790), and with I = 1/2, the κ(840). The real quark and/or gluon contents of these states are not fully understood, which the interpretation using effective theories most of them based on a linear realization of chiral symmetry cannot clarify.…”