Measurement of prompt J/ψ pair production in pp collisions at √s = 7 Tev

Production of prompt J/ψ meson pairs in proton-proton collisions at √s = 7 TeV is measured with the CMS experiment at the LHC in a data sample corresponding to an integrated luminosity of about 4.7 fb⁻¹. The two J/ψ mesons are fully reconstructed via their decays into μ⁺μ⁻ pairs. This observation provides for the first time access to the high-transverse-momentum region of J/ψ pair production where model predictions are not yet established. The total and differential cross sections are measured in a phase space defined by the individual J/ψ transverse momentum (p_T^J/ψ) and rapidity (|y^J/ψ|):|y^J/ψ| < 1.2 for p^J/ψ_T > 6.5 GeV/c; 1.2 < |y^J/ψ| < 1.43 for a p_T threshold that scales linearly with |y^J/ψ| from 6.5 to 4.5 GeV/c; and 1.43 < |y^J/ψ| < 2.2 for p^J/ψ_T > 4.5 GeV/c. The total cross section, assuming unpolarized prompt J/ψ pair production is 1.49 ± 0.07 (stat) ±0.13 (syst) nb. Different assumptions about the J/ψ polarization imply modifications to the cross section ranging from −31% to +27%.