Using QCD counting rules to identify the production of gluonium.

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Brodsky, Stanley J.
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Elsevier Science BV
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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 tau = 2. In contrast, quark-antiquark vertical bar q (q) over bar > scalar mesons have twist tau >= 3since they have nonzero orbital angular momentum, and multi-quark states such as vertical bar qq (q) over bar(q) over bar > tetraquarks yield twist tau >= 4. Thus, the production cross section for both vertical bar q (q) over bar > and vertical bar qq (q) over bar(q) over bar > 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 p(T) and fixed x(T) = 2 p(T)/root s will dominate higher twist mesons by at least two powers of p(T). 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(+) -> phi f(0) where the f(0) can be tested to be a glueball versus another type of scalar meson. (C) 2019 The Author(s). Published by Elsevier B.V.
©2019 Elsevier Science BV. We thank Richard Lebed and Jose R. Pelaez for helpful discussions. Work supported by Spanish grant MINECO: FPA2016-75654-C2-1-P, and by the US Department of Energy Contract No. DE-AC02-76SF00515.
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