Single-spin asymmetries in $$p^\uparrow p \rightarrow J/\psi +X$$ within a TMD approach: role of the color octet mechanism

Abstract

We calculate the transverse single-spin asymmetry (SSA) for J/ψ production in proton-proton collisions, within non-relativistic QCD, employing the transverse momentum dependent, generalized parton model, which includes both spin and intrinsic motion effects. In particular, we study the role of the color octet mechanism in accessing the gluon Sivers function. In doing that, we also show, within this approach, how the singularities coming from color octet terms in the low-PT region can be handled, leading to finite cross sections. Predictions for both unpolarized cross sections and SSAs are given and compared against PHENIX data. Estimates for LHCb in the fixed target mode are also presented. * Electronic address: umberto.dalesio@ca.infn.it † Electronic address: francesco.murgia@ca.infn.it ‡ Electronic address: cristian.pisano@ca.infn.it § Electronic address: rajesh.sangem@ca.infn.it

J/ψ meson production in SIDIS: matching high and low transverse momentum

“…Moreover, J/ψ production in both ep [12][13][14][15] and pp collisions [12,[16][17][18][19] has been proposed lately as a tool to access gluon TMDs. Similar studies have also been carried out within the so-called generalized parton model approach [20][21][22][23][24][25][26][27]. From the experimental point of view, these reactions should have a very clean signature due to the large branching ratio of the J/ψ leptonic decay modes.…”

Investigating the Transverse Momentum Dependent Gluon Sivers Function in Quarkonium Production at pp Colliders

“…See Refs. [71][72][73][74] for more details and for tables collecting the colour factors for all Feynman diagrams contributing to the partonic processes involved in J/ψ production.…”

“…The notation in these equations should be self-explicative, see however [71][72][73][74] for more details. We only notice that, as already discussed, in the CGI-GPM we have to take into account two independent gluon Sivers functions, named d-type and f -type, with a terminology that recalls their origin in the two different ways to neutralize colour.…”

“…In addition, let us recall that for the processes of interest here the role played by the quark contributions is quantitatively marginal. For the gluon case we adopt k 2 ⊥g = 1 GeV 2 from analyses of J/ψ production cross sections in pp collisions [71,73].…”

“…In this respect, inclusive particle production at low transverse momentum in the central rapidity region is the most favourable enviroment. Higgs [69,70] and quarkonium [71][72][73][74] production in gluon-fusion dominated proton-proton collisions are the most relevant examples, but a variety of other processes have been considered. Among them we mention: inclusive jet [75], pion and photon production in proton-proton collisions at mid-rapidities [72,76], heavy-quark pair [75,77,78] and quarkonium [79] pro-duction, quarkonium plus jet/photon [80,81] or dijet [82,83] production in proton-proton and lepton-proton collisions.…”