Abstract
We report on the inclusive production cross sections of {mathrm{J}/psi }, {psi (mathrm{2S})}, mathrm{Upsilon }(1S), mathrm{Upsilon }(2S) and mathrm{Upsilon }(3S), measured at forward rapidity with the ALICE detector in mathrm{pp} collisions at a center-of-mass energy sqrt{s}=8 TeV. The analysis is based on data collected at the LHC and corresponds to an integrated luminosity of 1.23 pb^{-1}. Quarkonia are reconstructed in the dimuon-decay channel. The differential production cross sections are measured as a function of the transverse momentum {p_mathrm{T}} and rapidity y, over the {p_mathrm{T}} ranges 0<{p_mathrm{T}}<20 GeV/c for {mathrm{J}/psi }, 0<{p_mathrm{T}}<12 GeV/c for all other resonances, and for 2.5<y<4. The cross sections, integrated over {p_mathrm{T}} and y, and assuming unpolarized quarkonia, are sigma _{{mathrm{J}/psi }} = 8.98pm 0.04pm 0.82 upmu b, sigma _{{psi (mathrm{2S})}} = 1.23pm 0.08pm 0.22 upmu b, sigma _{mathrm{Upsilon }mathrm{(1S)}} = 71pm 6pm 7 nb, sigma _{mathrm{Upsilon }mathrm{(2S)}} = 26pm 5pm 4 nb and sigma _{mathrm{Upsilon }mathrm{(3S)}} = 9pm 4pm 1 nb, where the first uncertainty is statistical and the second one is systematic. These values agree, within at most 1.4sigma , with measurements performed by the LHCb collaboration in the same rapidity range.
Highlights
The hadronic production of quarkonia, bound states of either a charm and anti-charm quark pair (e.g. J/ψ and ψ(2S)) or a bottom and anti-bottom quark pair (e.g. Υ(1S), Υ(2S) and Υ(3S)), is generally understood as the result of a hard scattering that produces the heavy-quark pair, followed by the evolution of this pair into a colorless bound state
The differential production cross sections are measured as a function of the transverse momentum pT and rapidity y, over the pT ranges 0 < pT < 20 GeV/c for J/ψ, 0 < pT < 12 GeV/c for all other resonances, and for 2.5 < y < 4
The following subsystems are used for measuring the quarkonium production cross sections at forward rapidity: the Muon Spectrometer [11], the first two layers of the Inner Tracking System (ITS) [12], the V0 scintillator hodoscopes [13] and the T0 Cherenkov counters [14]
Summary
The hadronic production of quarkonia, bound states of either a charm and anti-charm quark pair (e.g. J/ψ and ψ(2S)) or a bottom and anti-bottom quark pair (e.g. Υ(1S), Υ(2S) and Υ(3S)), is generally understood as the result of a hard scattering that produces the heavy-quark pair, followed by the evolution of this pair into a colorless bound state. The differential production cross sections are measured as a function of the transverse momentum pT and rapidity y, over the pT ranges 0 < pT < 20 GeV/c for J/ψ, 0 < pT < 12 GeV/c for all other resonances, and for 2.5 < y < 4. Our measurement extends the transverse momentum reach of the J/ψ cross section from pT = 12 GeV/c up to pT = 20 GeV/c with respect to results from LHCb [7]. Our measurement provides a unique cross-check of these results. It is the first time ALICE measures the Υ(3S) cross section. All cross sections reported here are inclusive and contain, on top of the direct production of the quarkonium, a contribution from the decay of higher-mass excited states.
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