ϒ production in pp and pA collisions: from RHIC to the LHC

Abstract

I discuss Υ production in pp collisions at RHIC, Tevatron and LHC energies, in particular the behaviour of the differential cross section in rapidity and the impact of QCD corrections on the P T differential cross section. I also emphasise the very good agreement between the parameter-free predictions of the Colour-Singlet Model (CSM) and the first LHC data, especially in the region of low transverse momenta, which is the most relevant one for heavyion studies. I also show that the CSM predicts Υ cross-section ratios in agreement with the most recent LHC data. I then briefly discuss the nuclear-matter effects on Υ production at RHIC and the LHC in p(d)A collisions and, by extension, in AA collisions. I argue that a) the Υ break-up probability can be neglected, at RHIC and the LHC, b) gluon shadowing -although non-negligible-is not strong enough to describe forward RHIC data, c) backward RHIC data hints at a gluon EMC effect, possibly stronger than the quark one. Outlooks for the LHC pPb run are also presented.

Energy dependence of direct-quarkonium production in $$\varvec{pp}$$ p p collisions from fixed-target to LHC energies: complete one-loop analysis

“…The agreement is a bit less good for ψ(2S) if we stick only to the default/central value. This is not at all a surprise and is in line with the previous conclusions made in [28][29][30][31]. In fact, strangely enough, it seems that it is only at low energies (below √ s = 100 GeV) that the CO contributions would be needed to describe the data.…”

“…The inability of colour-octet dominance within NRQCD to provide a global description of both low and large P T data is in line with the recent findings [28][29][30][31] that the sole LO colour-singlet contributions are sufficient to account for the magnitude of the total cross section and its dependence in rapidity, dσ/dy, from RHIC, Tevatron all the way to LHC energies. Any additional contribution in this energy range creates a surplus 1 as compared to data.…”

Next-to-leading-order QCD corrections to the yields and polarisations of J/ψ and $ Y $ directly produced in association with a Z boson at the LHC

“…They are also in agreement [19][20][21] with the existing data from RHIC [22] energy all the way up to that of the LHC [23][24][25][26][27][28][29][30]. CO channels are most likely not needed to account for low P T data -and thus for the P T integrated yields.…”

Quarkonium production in the LHC era: QCD corrections and new observables

“…As regards the P T differential cross section, the upper bound of the NNLO CSM predictions of the P T differential cross section is getting closer to the experimental data, especially at mid P T , as previously found for ϒ [10,28] and for J/ψ [11,26,27]. However, the NNLO evaluation is not a complete NNLO calculation.…”

“…For the time being, the most one can tell from the data-theory comparison in the framework of the CSM and the approximate NNLO is that below, say P T = 15 GeV, the upper uncertainty band of the NNLO agrees with the data -the same observation also holds for the J/ψ [11,26,27] while, for the ϒ(nS), the agreement is clearly much better [10,28]. Whether this has some physical meaning is a question that would only be answered once one has a full NNLO computation and/or once the LHC experimental collaborations release polarisation measurement for prompt ψ(2S) which would be precise enough to rule out the predictions from either the CSM or from the CO dominance.…”