Measurement of J/Ψ production in pp collisions at $\sqrt{s}=7$ TeV

Abstract

The production of J/ψ mesons in proton-proton collisions at √ s = 7 TeV is studied with the LHCb detector at the LHC. The differential cross-section for prompt J/ψ production is measured as a function of the J/ψ transverse momentum p T and rapidity y in the fiducial region p T ∈ [0; 14] GeV/c and y ∈ [2.0; 4 cross-section and fraction of J/ψ from b-hadron decays are also measured in the same p T and y ranges. The analysis is based on a data sample corresponding to an integrated luminosity of 5.2 pb −1 . The measured cross-sections integrated over the fiducial region are 10.52 ± 0.04 ± 1.40−2.20 µb for prompt J/ψ production and 1.14 ± 0.01 ± 0.16 µb for J/ψ from b-hadron decays, where the first uncertainty is statistical and the second systematic. The prompt J/ψ production cross-section is obtained assuming no J/ψ polarisation and the third error indicates the acceptance uncertainty due to this assumption.

Observation of double charm production involving open charm in pp collisions at $ \sqrt {s} = {7}\;{\text{TeV}} $

“…In the LHCb fiducial region (2 < y J/ψ < 4.5, p T J/ψ < 10 GeV/c), where y J/ψ and p T J/ψ stand for rapidity and transverse momentum respectively, the calculated J/ψ J/ψ production cross-section is 4.1±1.2 nb [12] in agreement with the measured value of 5.1 ± 1.0 ± 1.1 nb [13]. Similar calculations for the gg → J/ψ cc and gg → cccc matrix elements exist [14,15].…”

“…Using this equation and the measured single charm cross-sections given in [1,2] together with the effective cross-section measured in multi-jet events at the Tevatron σ DPS eff = 14.5 ± 1.7 +1.7 −2.3 mb [16], the size of this contribution is estimated (see table 1). However, this approach has been criticized as being too naive [17].…”

“…Table 4. Yields, S, and contamination from b-hadron decays, f [13,26] for the J/ψ → µ + µ − , and a modified Novosibirsk function [27] for the…”

“…The fit model is based on the probability 2 The functional form is inspired by the χ 2 distribution.…”

“…As the cross-sections of open charm [1] and charmonium [2] production are large, the question of multiple production of these states in a single proton-proton collision naturally arises. Recently, studies of double charmonium and charmonium with associated open charm production have been proposed as probes of the quarkonium production mechanism [3].…”