Scalar mesons and the fragmented glueball

Abstract

The center-of-gravity rule is tested for heavy and light-quark mesons. In the heavy-meson sector, the rule is excellently satisfied. In the light-quark sector, the rule suggests that the a0(980) could be the spin-partner of a2(1320), a1(1260), and b1(1235); f0(500) the spin-partner of f2(1270), f1(1285), and h1(1170); and f0(980) the spin-partner of f2′(1525), f1(1420), and h1(1415). From the decay and the production of light scalar mesons we find a consistent mixing angle θs=(14±4)∘. We conclude that f0(980) is likely “octet-like” in SU(3) with a slightly larger ss¯ content and f0(500) is SU(3) “singlet-like” with a larger nn¯ component. The a0(1450), K0⁎(1430), f0(1500) and f0(1370) are suggested as nonet of radial excitations. The scalar glueball is discussed as part of the wave function of scalar isoscalar mesons and not as additional “intruder”. It seems not to cause supernumerosity.