Using QCD counting rules to identify the production of gluonium

Abstract

The empirical identification of bound states of gluons has remained a central goal of hadron spectroscopy. We suggest an experimentally challenging, but model–independent way to assess which zero charge, isospin-zero mesons have a large gluonium light-front wavefunction component in the quark and gluon Fock space of QCD. Our method exploits QCD counting rules which relate the power-law fall-off of production amplitudes at high momentum transfer to the meson's twist (dimension minus spin of its minimum interpolating operators). Scalar 0+ glueballs composed of two valence gluons with zero internal orbital angular momentum have twist τ=2. In contrast, quark-antiquark |qq¯〉 scalar mesons have twist τ≥3 since they have nonzero orbital angular momentum, and multi-quark states such as |qqq¯q¯〉 tetraquarks yield twist τ≥4. Thus, the production cross section for both |qq¯〉 and |qqq¯q¯〉 mesons will be suppressed by at least one power of momentum transfer relative to glueball production. For example, in single inclusive particle hadroproduction AB→CX, the cross section for glueball production at high transverse momentum pT and fixed xT=2pTs will dominate higher twist mesons by at least two powers of pT.Similarly, in exclusive production processes at large CM energy and fixed CM angle, the glueball rate dominates by a power of s: we illustrate the method with a simple reaction, e−e+→ϕf0 where the f0 can be tested to be a glueball versus another type of scalar meson.