1303.5327 (J. P. Lansberg et al.)

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

J. P. Lansberg, C. Lorce

Contrary to earlier claims, we show that there are two kinds of colour-singlet contributions to the hadroproduction of J/psi in association with a W boson at orders alpha^3_S alpha and alpha^3 and that they are sizable, if not dominant over the colour-octet contributions. They come from the partonic processes s+g-> J/psi + c +W and q+q'-bar -> gamma* W -> J/psi W, which have systematically been overlooked 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 --and in turn of the NRQCD universality-- because of the sizable colour-singlet contribution and because of the small rate for this process at the LHC. 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 likely also extends to other processes naturally involving a light quark.

View original: http://arxiv.org/abs/1303.5327