npsm 새물리 New Physics : Sae Mulli

pISSN 0374-4914 eISSN 2289-0041


Research Paper

New Physics: Sae Mulli 2015; 65: 463-468

Published online May 29, 2015

Copyright © New Physics: Sae Mulli.

Revisiting the Scalar Meson $f_{0}(980)$ as a Pure Bound State of $K$ and $\bar{K}$ Mesons within the QCD Sum Rule

Hee-Jung LEE*

Department of Physics Education, Chungbuk National University, Cheongju 362-763, Korea


Received: March 30, 2015; Revised: April 21, 2015; Accepted: April 27, 2015

This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.


We analyze again, within the quantum chromodynamics (QCD) sum rule, whether the scalar meson $f_{0}(980)$ can be understood as a pure bound state of $K$ and $\bar{K}$ mesons. We calculate the direct instanton contributions to the QCD sum rule from the two quarks and the three quarks in the correlator consisting of the local interpolating current of a $K\bar{K}$ type for $f_{0}(980)$. We analyze the QCD sum rule with the direct instanton contributions and the contributions from the operator expansion product (OPE), and find that the direct instanton contribution from the two quarks is dominant in the QCD sum rule with a definite negative. As a result, understanding $f_{0}(980)$ as a pure bound state of $K$ and $\bar{K}$ mesons seems to be difficult. This result is the same as the previous result from the analysis of the QCD sum rule with the contributions from the OPE only.

Keywords: Instanton, Scalar mesons, QCD sum rule, OPE