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" role="presentation" style="border: 0px; font-variant: inherit; font-stretch: inherit; line-height: normal; font-family: inherit; margin: 0px; padding: 0px; vertical-align: baseline; outline: 0px; display: inline; word-spacing: normal; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; position: relative;">s√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 intoμ + 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 T J/ψ > 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 T J/ψ > 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%.