The status of glueballs

Abstract

Calculations within QCD (lattice and sum rules) find the lightest glueball to be a scalar with mass in the range of about 1000–1700 MeV. Several phenomenological investigations are discussed which aim at the identification of the scalar meson nonets of lowest mass and the super-numerous states if any. Results on the flavour structure of the light scalars f 0 (500), f 0 (980) and f 0 (1500) are presented; the evidence for f 0 (1370) is scrutinized. A significant surplus of leading clusters of neutral charge in gluon jets is found at LEP in comparison with MCs, possibly a direct signal for glueball production; further studies with more energetic jets at LHC are suggested. As a powerful tool in the identification of the scalar nonets or other multiplets, along with signals from glueballs we propose the exploration of symmetry relations for decay rates of C = +1 heavy quark states like χ c or χ b . Results from χ c decays are discussed; they are not in support of a tetra-quark substructure of f 0 (980). A minimal scenario for scalar quarkonium-glueball spectroscopy is presented.