The experimental status of glueballs

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 massin theraingefrom 1 to 2 GeV/c(2); pseudoscalar and tensor glueballs 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 pseucloscalar glueballs are weak at best. Theoretical expectations of phenomenological models and QCD on the lattice are briefly discussed. (C) 2009 Elsevier B.V. All rights reserved.