Possible solution of the J/psi production puzzle

TL;DR

It is argued that the s-channel cut contribution to J/psi hadroproduction can be significantly larger than the usual cut contribution of the color-singlet mechanism, which is known to underestimate the experimental measurements.

Abstract

We argue that the s-channel cut contribution to J/psi hadroproduction can be significantly larger than the usual cut contribution of the color-singlet mechanism, which is known to underestimate the experimental measurements. A scenario accounting for intermediate $c\bar(c)$ interactions is proposed that reproduces the data at low- and mid-range transverse momenta P_T from the Fermilab Tevatron and BNL Relativistiv Heavy Ion Collider. The J/psi produced in this manner are polarized predominantly longitudinally.

Figures (4)

• Figure 1: (Color online). (a,b) Leading-order (LO) $s$-channel cut diagrams contributing to $gg\to \mathcal{Q}g$ with direct and crossed box diagrams employing the $c\bar{c}\,J/\psi$ vertex. The crosses indicate that the quarks are on-shell. (c) Box diagram with $c\bar{c}\mathcal{Q}g$ contact term mandated by gauge invariance.
• Figure 2: Example of the mechanisms (a) contributing to the dressing of the 3-point function $\Gamma^{(3)}$ and (b) responsible for the 4-point function $\Gamma^{(4)}$: the external gluon is attached here within gluon loops of the dressed vertex, thus producing a diagram without poles and with a kinematic behavior genuinely different from the initial 3-point vertex.
• Figure 3: (Color online). (a) Comparison between polarized ($\sigma_T$ and $\sigma_L$) and unpolarized ($\sigma_{\text{tot}}$) cross sections [with parameters $a=4$, $\kappa=4.5$ GeV in Eq. (\ref{['eq:interpolate']})], LO CSM contributions, and CDF experimental data Abe:1997yz at the Tevatron ($\sqrt{s}=1.8$ TeV, pseudorapidity $|\eta|<0.6$). (b) Comparison between $\sigma_T$, $\sigma_L$, $\sigma_{\text{tot}}$ and PHENIX data Adare:2006kf at RHIC ($\sqrt{s}=200$ GeV, rapidity $|y|<0.35$).
• Figure 4: Prompt $J/\psi$ polarization: theory vs. CDF data Abulencia:2007us.