https://doi.org/10.1140/epjc/s10052-015-3527-1
Regular Article - Theoretical Physics
Energy dependence of direct-quarkonium production in 
collisions from fixed-target to LHC energies: complete one-loop analysis
1
Institute of High Energy Physics, CAS, P.O.Box 918(4), Beijing, 100049, China
2
Theoretical Physics Center for Science Facilities, CAS, Beijing, 100049, China
3
IPNO, Université Paris-Sud, CNRS/IN2P3, 91406, Orsay, France
* e-mail: lansberg@in2p3.fr
Received:
2
April
2015
Accepted:
17
June
2015
Published online:
8
July
2015
We compute the energy dependence of the 
-integrated cross section of directly produced quarkonia in pp collisions at next-to-leading order (NLO), namely up to 
, within nonrelativistic QCD (NRQCD), treating the -integrated and the -differential cross sections as two different observables. The colour-octet NRQCD parameters needed to predict the -integrated yield can thus be extracted from the fits of the -differential cross sections at mid and large . For the first time, the total cross section is evaluated in NRQCD at full NLO accuracy using the recent NLO fits of the -differential yields. Both the normalisation and the energy dependence of the 
, 
and 
we obtained disagree with the data except when using the fit results of Butenschoen and Kniehl. If one disregards the colour-octet contribution, the existing data in the TeV range are well described by the contribution in the colour-singlet model – which, at 
, however, shows an unphysical energy dependence. A similar observation is made for 
. All this underlines the necessity for a resummation of initial-state radiations in both channels, which is, however, beyond the scope of this article. In any case, past claims that colour-octet transitions are dominantly responsible for low- quarkonium production are not supported by our results.
© SIF and Springer-Verlag Berlin Heidelberg, 2015
