Publication: Using QCD counting rules to identify the production of gluonium.
Full text at PDC
Brodsky, Stanley J.
Advisors (or tutors)
Elsevier Science BV
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.