Narrow Results

We report here on recent advances that shed light on the topic of scalar meson sector, which is controversial up to date. We study the scattering and spectroscopy of the strongly interacting mesons in coupled channels with quantum numbers J^PC = 0⁺⁺ and I = 0 and I = 1/2, up to a center of mass energy . Our framework is based on Unitary Chiral Perturbation Theory, but extended now to include many more channels. The resonant content of our fits is discussed, with the appearence of σ, f₀(980), f₀(1310), f₀(1500), f₀(1710) and f₀(1790) for I = 0 and the κ and the for I = 1/2.

I report on a recent work¹ done in collaboration with G. Colangelo and H. Leutwyler, where we demonstrated that the ππ scattering amplitude has on the second sheet near the threshold a pole with the quantum numbers of the vacuum. The proof does not involve models or parametrizations, but relies on the Roy equations which are derived from first principles. The knowledge of ππ scattering from ChPT and low energy theorems allows a precise determination of the pole position of the lowest hadronic resonance.

This manuscript sheds light on the puzzle created by the finding of two resonances with same quantum numbers and very similar mass but which possess very different decay properties. One of them, f₀(1790), has been found in the J/Ψ → φπ⁺π⁻ process while the other, f₀(1800), in J/Ψ → γωφ. As we shall discuss in this manuscript, our studies show that these two states are distinct to each other but only one of them is a new state, while the other one is the manifestation of the known f₀(1710). We also provide an explanation for the different decay properties of these states.