Two-photon width and gluonic component of sigma/f_0(600)

TL;DR

This paper analyzes pi pi and gamma gamma scattering data below 700 MeV using an improved analytic K-matrix model to determine the two-photon width of the sigma/f_0(600) resonance and its gluonic component.

Contribution

It introduces an enhanced analytic K-matrix model to study the sigma/f_0(600) resonance's two-photon decay and assesses the resonance's internal structure and gluonic content.

Findings

The total radiative width of sigma/f_0(600) is approximately 3.9 keV.

Rescattering processes dominate the two-photon decay, indicating insensitivity to internal structure.

The direct decay component is small, consistent with an unmixed glueball hypothesis.

Abstract

We analyse data on pi pi and gamma gamma scattering below 700 MeV within an improved analytic K-matrix model. This model is based on an effective theory with couplings between resonances, hadrons and photons. The two-photon decay of a resonance can proceed through intermediate transition into charged hadrons (here: pi^+ pi^-) and their subsequent annihilation or through a ``direct'' transition into photons. Our analysis confirms the rather large total radiative width of the sigma/f_0(600) resonance which we find as (3.9 \pm 0.6) keV but suggests its dominance by the pi pi rescattering process. This process is not sensitive to the internal structure of the resonance contrary to the direct component which we find small, (0.13 \pm 0.05) keV, and well consistent with the expectations for an unmixed glueball according to the QCD sum rule calculations.