Measurement of the Prompt J/Psi Pair Production Cross Section in pp Collisions at sqrt(s) = 8 TeV with CMS

The cross section for the prompt production of J/ψ [J/Psi] meson pairs in proton-proton collisions at √ s[sqrt(s)] = 8 TeV at the LHC from a sample corresponding to an integrated luminosity of 20.2±0.5 fb−1 [inverse femtobarns] has been measured with the CMS detector. It provides unique insight into particle production and proton structure in proton-proton (pp) collisions. The two J/ψ mesons are fully reconstructed in their µ +µ −[mu+ mu-] decay. An acceptance region is defined by the individual J/ψ transverse momentum pT J/ψ [J/Psi pT] and rapidity |y J/ψ| [J/Psi Rapidity]. The total fiducial cross section assuming unpolarized prompt J/ψ pair production is found to be σ (fid)[sigma_fid] = 195.7 ± 11.1 (stat) ± 22.1 (syst) ± 5.1 (lumi) ± 2.3 (BF) pb. The differential cross sections for prompt J/ψ pair production within this acceptance region are measured in eight event variables. Most predictions for particle production in pp collisions at the LHC assume dominance of single parton (gluon, quark) interactions (SPS) at the leading order perturbation theory. This assumption is tested with the final state measured in this analysis. Significant contributions from next-to-leading order processes and double parton scattering (DPS) are observed. In addition, the single J/ψ production cross section is estimated from theory and measured with pp collision data. Single J/ψ production is compared to the pair production via DPS and quantified via an effective cross section. This quantity is further compared to several particle pair production processes. In particular, the J/ψ pair production probes the contributions of gluons. All particle production measurements with CMS depend on the precise knowledge of the LHC luminosity. A detector, the Pixel Luminosity Telescope, based on solid state technology is used to count charged particle tracks from pp collisions, a measure of the instantaneous v luminosity. The measurement is provided online for every crossing of the LHC beams. Tests of sensors and the development work for the detector are presented.