Measurement of Charmonium Production Cross Section at LHCb

The great abundance of charmonium states, collected from the start up of LHC, allows to study its production mechanism. In particular the total and differential $J/\psi$ production cross section are measured in the transverse momentum range [0;10] GeV/$c$ and in the pseudorapidity range $y \in$ [2.5;4]. The measurements are performed disentagling the prompt (direct production in $pp$ collisions and feed down from excited charmonium states) and delayed ($b$-hadron decays products) component.