Light Scalar Meson sigma(600) in QCD Sum Rule with Continuum

TL;DR

This paper uses QCD sum rules with tetraquark currents and continuum contributions to estimate the sigma(600) meson mass, accounting for its broad width and resonance nature.

Contribution

It introduces a comprehensive analysis of the sigma(600) using all local tetraquark currents and continuum effects within QCD sum rules, providing a refined mass estimate.

Findings

Sigma(600) mass estimated at 530 MeV ± 40 MeV

Mass shows increasing trend with Borel mass, indicating broad resonance width

Inclusion of pi-pi continuum improves sum rule stability

Abstract

The light scalar meson sigma(600) is known to appear at low excitation energy with very large width on top of continuum states. We investigate it in the QCD sum rule as an example of resonance structures appearing above the corresponding thresholds. We use all the possible local tetraquark currents by taking linear combinations of five independent local ones. We ought to consider the pi-pi continuum contribution in the phenomenological side of the QCD sum rule in order to obtain a good sum rule signal. We study the stability of the extracted mass against the Borel mass and the threshold value and find the sigma(600) mass at 530 MeV +- 40 MeV. In addition we find the extracted mass has an increasing tendency with the Borel mass, which is interpreted as caused by the width of the resonance.