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Compact Muon Solenoid
LHC, CERN

CMS-PAS-BPH-11-021
Measurement of the Prompt Double J/ψ Production Cross Section in pp Collisions at (s)= 7 TeV
Abstract: The cross section for the simultaneous production of two J/ψ mesons in proton-proton collisions at s= 7 TeV at the LHC from a sample corresponding to an integrated luminosity of 4.73 ± 0.12 fb1 has been measured with the CMS detector. The two J/ψ mesons are fully reconstructed via their decays into μ+μ, and the signal yield is extracted with an extended maximum-likelihood fit. The acceptance region is defined by the individual J/ψ transverse momentum (pJ/ψT) and rapidity (|yJ/ψ|): pJ/ψT> 6.5 GeV/c for |yJ/ψ|< 1.2, pJ/ψT> 6.5 4.5 GeV/c (where the pT threshold scales linearly from 6.5 to 4.5 GeV/c) in the region 1.2 <|yJ/ψ|< 1.43, and pJ/ψT> 4.5 GeV/c for 1.43 <|yJ/ψ|< 2.2. The total cross section assuming unpolarized prompt double J/ψ production is found to be σ= 1.49 ± 0.07 ± 0.14 nb, where the first uncertainty is statistical and the second is systematic. Different extreme assumptions about the J/ψ polarization can increase the cross section by as much as 27% or decrease it by as much as 31%. The differential cross section is measured in bins of the double J/ψ invariant mass, the absolute difference in rapidity of the two J/ψ mesons, and the transverse momentum of the double J/ψ system. The double J/ψ invariant mass distribution is examined for possible contributions from ηb production.
Compact Muon Solenoid
LHC, CERN