The Experimental Status of Glueballs

TL;DR

This paper reviews the experimental evidence for glueballs, highlighting strong evidence for a scalar glueball mixed with mesons, while evidence for tensor and pseudoscalar glueballs remains weak, and discusses theoretical predictions from QCD and lattice models.

Contribution

It provides a comprehensive overview of the current experimental status of glueballs and compares findings with theoretical models and lattice QCD predictions.

Findings

Strong evidence for scalar glueball existence

Weak evidence for tensor and pseudoscalar glueballs

Discussion of theoretical and lattice QCD predictions

Abstract

Glueballs and other resonances with large gluonic components are predicted as bound states by Quantum Chromodynamics (QCD). The lightest (scalar) glueball is estimated to have a mass in the range from 1 to 2 GeV/c**2; a pseudoscalar and tensor glueball are expected at higher masses. Many different experiments exploiting a large variety of production mechanisms have presented results in recent years on light mesons with J(PC) = 0(++), 0(-+), and 2(++) quantum numbers. This review looks at the experimental status of glueballs. Good evidence exists for a scalar glueball which is mixed with nearby mesons, but a full understanding is still missing. Evidence for tensor and pseudoscalar glueballs are weak at best. Theoretical expectations of phenomenological models and QCD on the lattice are briefly discussed.