Nonet Classification of Scalar/Isoscalar Resonances in the Mass Region below 1900 MeV: Observation of the Lightest Scalar Glueball

Abstract

We summarize the results of the investigation of the $IJ^{PC}=00^{++}$ wave which is devoted to the search for the lightest scalar glueball. In the framework of the K-matrix formalism, the $q\bar q$-nonet classification of the scalar/isoscalar states is performed in the mass region below 1900 MeV basing on the following data: GAMS data for $π^-p\toπ^0π^0n$, $ηηn$, $ηη'n$; CERN-Münich data for $π^-p\toπ^+π^-n$; Crystal Barrel data for $p\bar p\toπ^0π^0π^0$, $π^0π^0η$, $π^0ηη$; BNL data for $ππ\to K\overline K$. It is shown the existence of an extra state for $q\bar q$ classification: this state is a good candidate for the lightest scalar glueball. Analysis of the glueball/$q\bar q$ mixing shows that the glueball state has mainly dispersed over three real resonances: $f_0(1300)$, $f_0(1500)$ and $f_0(1530^{+90}_{-250})$. The broad resonance with complex mass $m=1530^{+90}_{-250}-i(560\pm 140)$ MeV is descendant of the pure glueball. The restored mass of the pure glueball is equal to 1695 MeV. This value agrees well with the results of lattice gluodynamics.