Hadroproduction of J/psi and Upsilon in association with a heavy-quark pair

TL;DR

This work computes the leading-order hadroproduction cross sections for direct ${\rm J}/\psi$ and $\Upsilon$ production in association with a heavy-quark pair within NRQCD, using a spin-projector formalism and a custom MadGraph setup to handle $^3S_1^{[1]}$ states. It demonstrates that the fragmentation approximation substantially underestimates the full LO results in Tevatron kinematics and identifies the dominance of diagrams where the quarkonium is produced from two separate quark lines. Polarisation analysis shows that quarkonia produced via $Q\bar Q$ partners remain unpolarised across the explored $P_T$ range, unlike the $Q+g$ channel which tends to transverse polarisation at high $P_T$. The findings highlight the importance of full LO calculations for interpreting NRQCD contributions to inclusive quarkonium production and suggest new experimental signatures, with implications for matching to NLO corrections and data from the Tevatron and LHC.

Abstract

We calculate the cross sections for the direct hadroproduction of J/psi and Upsilon associated with a heavy-quark pair of the same flavour at leading order in alpha_S and v in NRQCD. These processes provide an interesting signature that could be studied at the Tevatron and the LHC and also constitute a gauge-invariant subset of the NLO corrections to the inclusive hadroproduction of J/psi and Upsilon. We find that the fragmentation approximation commonly used to evaluate the contribution of these processes to the inclusive quarkonium production sizeably underestimates the exact calculation in the kinematical region accessible at the Tevatron. Both J/psi and Upsilon are predicted to be unpolarised, independently of their transverse momentum.