The Status of Glueballs

TL;DR

This paper reviews the current understanding of glueballs in QCD, discussing their theoretical predictions, phenomenological identification, and experimental signals, especially focusing on scalar mesons and potential production evidence.

Contribution

It provides a comprehensive overview of glueball properties, flavor structures, and experimental signals, proposing new methods for identifying scalar nonets and glueballs in particle decays.

Findings

Lightest glueball likely a scalar with mass 1000-1700 MeV

Evidence for glueball production in gluon jets at LEP

Decay rate symmetry relations as tools for identifying multiplets

Abstract

Calculations within QCD (lattice and sum rules) find the lightest glueball to be a scalar and 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 f0(500), f0(980) and f0(1500) are presented; the evidence for f0(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 chi-c or chi-b. Results from chi-c decays are discussed; they are not in support of a tetra-quark substructure of f0(980). A minimal scenario for scalar quarkonium - glueball spectroscopy is presented.