Study of Light Scalars, the learned Lessons

TL;DR

This paper investigates the production mechanisms and nature of light scalar mesons, providing evidence for their four-quark structure through theoretical models, scattering amplitudes, and experimental data analysis.

Contribution

It demonstrates that light scalar mesons like 00 and f_0(980) are predominantly four-quark states, supported by scattering, decay, and production mechanisms.

Findings

Data supports four-quark structure of 00 and f_0(980)

Kaon loop mechanism confirms four-quark transitions in 00 decays

Light scalars are produced via four-quark transitions in two-photon collisions

Abstract

Attention is paid to the production mechanisms of the light scalars that reveal their nature. In the linear sigma model it is revealed the chiral shielding of the \sigma(600) meson and shown that the \sigma field is described by its four-quark component. The \pi\pi scattering amplitude is constructed taking into account the \sigma(600) and f_0(980) mesons, the chiral shielding of \sigma (600), the \sigma(600)-f_0(980) mixing, and results, obtained on the base of the chiral expansion and the Roy equations. The data agree with the four-quark nature of \sigma (600) and f_0(980). It is shown, that the kaon loop mechanism of the $\phi$ radiative decays into the light scalar mesons, which is ratified by experiment, is the four-quark transition and points to the four-quark nature of the light scalars. It is shown also, that the light scalars are produced in the two photon collisions via four-quark transitions in contrast to the classic P wave tensor q\bar q mesons, which are produced via two-quark transitions \gamma\gamma\to q\bar q, that points to the four-quark nature of the light scalar mesons, too. A programme of further investigations is laid down.