Measurement of quarkonium production at forward rapidity in pp collisions at $\sqrt{s}$= 7 TeV

Abstract

The inclusive production cross sections at forward rapidity of J/$ψ$, $ψ$(2S), $Υ$(1S) and $Υ$(2S) are measured in pp collisions at $\sqrt{s} = 7$ TeV with the ALICE detector at the LHC. The analysis is based in a data sample corresponding to an integrated luminosity of 1.35 pb$^{-1}$. Quarkonia are reconstructed in the dimuon-decay channel and the signal yields are evaluated by fitting the $μ^+μ^-$ invariant mass distributions. The differential production cross sections are measured as a function of the transverse momentum $p_{\rm T}$ and rapidity $y$, over the ranges $0 < p_{\rm T} < 20$ GeV/$c$ for J/$ψ$, $0 < p_{\rm T} < 12$ GeV/$c$ for all other resonances and for $2.5 < y < 4$. The measured cross sections integrated over $p_{\rm T}$ and $y$, and assuming unpolarized quarkonia, are: $σ_{J/ψ} = 6.69 \pm 0.04 \pm 0.63$ $μ$b, $σ_{ψ^{\prime}} = 1.13 \pm 0.07 \pm 0.14$ $μ$b, $σ_{Υ{\rm(1S)}} = 54.2 \pm 5.0 \pm 6.7$ nb and $σ_{Υ{\rm (2S)}} = 18.4 \pm 3.7 \pm 2.2$ nb, where the first uncertainty is statistical and the second one is systematic. The results are compared to measurements performed by other LHC experiments and to theoretical models.