Reassessing the importance of the colour-singlet contributions to direct J/psi+W production at the LHC and the Tevatron

TL;DR

This paper demonstrates that colour-singlet processes significantly contribute to J/psi + W production at the LHC and Tevatron, challenging the assumption that this process is a clean probe of the colour-octet mechanism.

Contribution

It identifies and quantifies previously neglected colour-singlet contributions to J/psi + W production, showing they are sizable and complicate the interpretation of experimental results.

Findings

Colour-singlet contributions are comparable or dominant over colour-octet ones.

The processes sg -> J/psi + c + W and q q'-bar -> gamma*/Z* W are significant.

Disentangling colour-octet signals from colour-singlet and double-parton scattering is challenging.

Abstract

We show that the colour-singlet contributions to the hadroproduction of J/psi in association with a W boson are sizable, if not dominant over the colour-octet contributions. They are of two kinds, sg -> J/psi + c + W at alpha^3_S alpha and q q'-bar -> gamma*/Z* W -> J/psi W at order alpha^3. These have not been considered in the literature until now. Our conclusion is that the hadroproduction of a J/psi in association with a W boson cannot be claimed as a clean probe of the colour-octet mechanism. The rate are small even at the LHC and it will be very delicate to disentangle the colour-octet contributions from the sizable colour-singlet ones and from the possibly large double-parton-scattering contributions. During this analysis, we have also noted that, for reactions such as the production of a J/psi by light quark-antiquark fusion, the colour-singlet contribution via an off-shell photon is of the order of the expectation from the colour-octet contribution via an off-shell gluon. This is relevant for inclusive production at low energies close to the threshold. Such an observation also likely extends to other processes naturally involving light-quark annihilation.