The lightest scalar glueball

Recent studies of meson spectra have enabled the resonance structure of the IJ(PC) = 00(++), 10(++), 02(++), 12(++), and IJ(P) = 1/2 0(+) waves to be found for masses ranging up to 1900 MeV, thus fully reconstructing the 1(3)P0q (q) over bar and 2(3)P0q (q) over bar meson multiplets. There is firm experimental evidence for the existence of five scalar (isoscalar) states in this mass range, four of which are q (q) over bar states and members of the 1(3)P0q (q) over bar and 2(3)P0q (q) over bar nonets, whereas the fifth falls out of the quark picture and displays all the properties of the lightest possible scalar glueball. A dispersion analysis of the 00(++) wave elucidates how the mixture of the pure glueball state (or gluonium) with neighbouring scalar q (q) over bar states forms: three scaler mesons, namely two relatively narrow f(0)(1300) and f(0)(1500) resonances and a very broad f(0)(1530(-250)(+90)) resonance, share the gluonium, the broad resonance being the gluonium's descendant and accounting for about 40 to 50% of its component.