Quarkonium results from LHCb

The mechanism for the production of quarkonia in hadronic collisions is not yet completely understood. It is well kown that the LO Colour Singlet Model (CSM) leads to predictions of the cross-sections which are in disagreement with the osbervations at High $P_T$. New theoretical approaches have been proposed in recent years. For example, the Non-Relativistic QCD factorisation formalism, in which Colour Octet diagrams are introduced. Another approach consists in extending the computation of the cross-sections in Colour Singlet Model up to the NNLO. In the Colour Evaporation Model (CEM) instead, the probability of forming a specific quarkonium state is assumed to be independent of the color of the $Q\bar{Q}$ pair. The debate is still open and experimental confirmations from the LHC experiments are needed to determine the reliability of the proposed models. Open charm can be produced in p-p collisions in association to a $J/\psi$ meson or in association to another open charm hadron. Predictions for the production cross-sections exist and are given by the LO perturbative QCD, where calculations are made for the processes $gg \rightarrow J/\psi J/\psi$, $gg \rightarrow J/\psi c\bar{c}$ and $gg |\rightarrow c\bar{c}c\bar{c}$. These predictions are affected by uncertainties that can amount to a factor of two due to the selection of the $\alpha_s$ scale. In p-p collisions contributions from other mechanisms are possible, such as Double Parton Scattering (DPS) in which the factorisation of the two PDF is assumed, or the intrinsic charm content of the proton (IC). Since such theories lead to different predictions for double charm (onium) cross-sections, experimental results from the LHC can give helpful hints and strong indications.