Inelastic J/psi and Upsilon hadroproduction

TL;DR

The paper proposes a perturbative QCD mechanism for prompt quarkonium hadroproduction based on a symmetric colour-octet two-gluon state with an extra gluon, offering a LO framework that enhances cross sections and aligns with Tevatron and RHIC data without invoking nonperturbative colour-octet contributions. It derives the lowest-order amplitude, computes the prompt J/psi yield, and extends the approach to psi' and Upsilon states, achieving good agreement with available data for multiple states and predicting LHC cross sections. It also analyzes alternative production channels (uncorrelated gluon-gluon pairs, associative production, and feed-down decays) and discusses energy and rapidity dependencies, polarization expectations, and uncertainties. Overall, the work suggests a perturbative mechanism that can describe high-energy quarkonium production more consistently across energies than conventional colour-singlet or NRQCD approaches, with tangible implications for LHC phenomenology.

Abstract

We consider the prompt hadroproduction of J/psi, psi' and the Upsilon (1S,2S,3S) states caused by the fusion of a symmetric colour-octet two-gluon state and an additional gluon. The cross sections are calculated in leading-order perturbative QCD. We find a considerable enhancement in comparison with previous perturbative QCD predictions. Indeed, the resulting cross sections are found to be consistent with the values measured at the Tevatron and RHIC, without the need to invoke non-perturbative `colour-octet' type of contributions.

Figures (10)

• Figure 1: (a) The 'bleaching' gluon subprocess used in the original 'colour-singlet' perturbative QCD estimates of prompt $J/\psi$ hadroproduction. (b) The perturbative QCD mechanism studied in this paper. In each case the subprocess $gg \to J/\psi~g$ is shown in bold.
• Figure 2: Lowest-order perturbative QCD diagrams for $J/\psi$ hadroproduction via gluon-gluon fusion with an additional gluon.
• Figure 3: A contribution to inclusive prompt $J/\psi$ production accompanied by gluon emissions from a $t$-channel gluon-pair in a colour-symmetric octet. Again, the hard subprocess is shown by bold particle lines.
• Figure 4: The transverse momentum ($Q_t$) distributions of inelastic $J/\psi$ and $\psi'$ production. The data are from Refs. CDFpsiprime. The upper and lower data sets for the $Q_t$ distribution of the $J/\psi$ correspond to the total (at $\sqrt S$ = 1.96 TeV) and prompt (at $\sqrt S$ = 1.8 TeV) $J/\psi$ yields respectively; recall that our QCD prediction is for prompt production only.
• Figure 5: The $Q_t$ distributions of the inelastic production of the $\Upsilon$ states, compared with Tevatron data up1.