Total J/Psi and Upsilon production cross section at the LHC: theory vs. experiment

Abstract

We evaluate the production cross section for direct J/Psi and Upsilon integrated in P_T for various collision energies in the QCD-based Colour-Singlet Model (CSM). We consider the LO contribution from gluon fusion whose P_T-integrated cross section shows a very good agreement with the Tevatron and LHC data, both for J/Psi and Upsilon. The rapidity distribution of this yield is evaluated in the central region relevant for the ATLAS and CMS detectors, as well as in the more forward region relevant for the ALICE and LHCb detectors. The results obtained here are compatible with those of other approaches within the range of the theoretical uncertainties which are admittedly very large. This suggests that the "mere" measurements of the yield at the LHC will not help disentangle between the different possible quarkonium production mechanisms. Yet, the comparison with the first LHC results by ALICE, ATLAS, CMS and LHCb confirms that the CSM correctly accounts for the P_T-integrated yield at sqrt(s)=7 TeV.