3,368 research outputs found

    Same-sign WW production in proton-nucleus collisions at the LHC as a signal for double parton scattering

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    The production of same-sign W-boson pairs from double parton scatterings (DPS) in proton-lead (p-Pb) collisions at the CERN Large Hadron Collider is studied. The signal and background cross sections are estimated with next-to-leading-order perturbative QCD calculations using nuclear parton distribution functions for the Pb ion. At sqrt(sNN) = 8.8 TeV the cross section for the DPS process is about 150 pb, i.e. 600 times larger than that in proton-proton collisions at the same centre-of-mass energy and 1.5 times higher than the pPb --> WW+2-jets single-parton background. The measurement of such a process, where 10 events with fully leptonic W's decays are expected after cuts in 2 pb^{-1}, would constitute an unambiguous DPS signal and would help determine the effective sigma_eff parameter characterising the transverse distribution of partons in the proton.Comment: 10 pages, 1 figure, 1 table. Tiny mods. Matches PLB published versio

    Double-parton scattering cross sections in proton-nucleus and nucleus-nucleus collisions at the LHC

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    Simple generic expressions to compute double-parton scattering (DPS) cross sections in high-energy proton-nucleus and nucleus-nucleus collisions, as a function of the corresponding single-parton cross sections, are presented. Estimates of DPS contributions are studied for two specific processes at LHC energies: (i) same-sign W-boson pair production in p-Pb, and (ii) double-J/psi production in Pb-Pb, using NLO predictions with nuclear parton densities for the corresponding single-parton cross sections. The expected DPS cross sections and event rates after typical acceptance and efficiency losses are also given for other processes involving J/psi and W,Z gauge bosons in p-Pb and Pb-Pb collisions at the LHC.Comment: 4 pages, 2 figures. Proceedings Hard-Probes'13 (Stellenbosch, South Africa) to appear in Nucl.Phys.

    Triple parton scatterings in high-energy proton-proton collisions

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    A generic expression to compute triple parton scattering (TPS) cross sections in high-energy proton-proton (pp) collisions is presented as a function of the corresponding single-parton cross sections and the transverse parton distribution in the proton encoded in an effective parameter σeff,TPS\sigma_{\rm eff,TPS}. The value of σeff,TPS\sigma_{\rm eff,TPS} is closely related to the similar effective cross section that characterizes double-parton scatterings, and amounts to σeff,TPS=12.5±4.5\sigma_{\rm eff,TPS} = 12.5 \pm 4.5 mb. Estimates for triple charm (cc\rm c\overline{c}) and bottom (bb\rm b\overline{b}) production in pp collisions at LHC and FCC energies are presented based on next-to-next-to-leading order perturbative calculations for single cc,bb\rm c\overline{c},\rm b\overline{b} cross sections. At s\sqrt{s}\approx 100 TeV, about 15% of the pp collisions produce three cc\rm c\overline{c} pairs from three different parton-parton scatterings.Comment: 4 pages, 2 figure

    Enhanced J/Psi-pair production from double parton scatterings in nucleus-nucleus collisions at the Large Hadron Collider

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    A generic expression of double-parton scattering cross sections in high-energy nucleus-nucleus (A-A) collisions is derived as a function of the corresponding single-parton hard cross sections and of the A-A event centrality. We consider the case of prompt-J/psi production in lead-lead (Pb-Pb) at the CERN Large Hadron Collider and find that about 20% (35%) of the J/psi events in minimum-bias (most central) collisions contain a second J/psi from double parton interactions. In Pb-Pb at 5.5 TeV, in the absence of final-state effects, about 240 double-J/psi events are expected per unit midrapidity and per inverse-nanobarn in the dilepton decay modes. The implications of double-J/psi production on the interpretation of the observed J/psi suppression in A-A collisions are discussed.Comment: 7 pages, 3 figures, 1 tabl

    Pair production of quarkonia and electroweak bosons from double-parton scatterings in nuclear collisions at the LHC

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    Cross sections for the concurrent production of pairs of quarkonia (J/psi, Upsilon) and/or gauge bosons (W, Z) from double-parton scatterings (DPS) in high-energy proton-nucleus and nucleus-nucleus collisions at the LHC are calculated. The estimates are based on next-to-leading-order perturbative QCD predictions, including nuclear modifications of the parton densities, for the corresponding single-scattering cross sections. Expected event rates for J/psi+J/psi, J/psi+Upsilon, J/psi+W, J/psi+Z, Upsilon+Upsilon, Upsilon+W, Upsilon+Z, and same-sign W+W production in their (di)leptonic decay modes, after typical acceptance and efficiency losses, are given for pPb and PbPb collisions.Comment: 4 pages. 2 figures. Proceedings Quark-Matter'14. To appear in NP

    Triple parton scatterings in proton-nucleus collisions at high energies

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    A generic expression to compute triple parton scattering (TPS) cross sections in high-energy proton-nucleus (pA) collisions is derived as a function of the corresponding single-parton cross sections and an effective parameter encoding the transverse parton profile of the proton. The TPS cross sections are enhanced by a factor of 9A20009\,A\approx 2000 in pPb compared to those in proton-nucleon collisions at the same center-of-mass energy. Estimates for triple charm (ccc\overline{c}) and bottom (bbb\overline{b}) production in pPb collisions at LHC and FCC energies are presented based on next-to-next-to-leading order (NNLO) calculations for cc,bbc\overline{c}, b\overline{b} single-parton cross sections. At sNN=8.8\sqrt{s_{NN}} = 8.8 TeV, about 10% of the pPb events have three ccc\overline{c} pairs produced in separate partonic interactions. At sNN=63\sqrt{s_{NN}} = 63 TeV, the pPb cross sections for triple-J/ψ/\psi and triple-bbb\overline{b} are O{\cal O}(1--10 mb). In the most energetic cosmic-ray collisions observed on earth, TPS ccc\overline{c}-pair cross sections equal the total p-Air inelastic cross section.Comment: 6 pages, 4 figures. arXiv admin note: text overlap with arXiv:1612.0558

    Performance of CMS muon reconstruction in pp collision events at sqrt(s) = 7 TeV

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    The performance of muon reconstruction, identification, and triggering in CMS has been studied using 40 inverse picobarns of data collected in pp collisions at sqrt(s) = 7 TeV at the LHC in 2010. A few benchmark sets of selection criteria covering a wide range of physics analysis needs have been examined. For all considered selections, the efficiency to reconstruct and identify a muon with a transverse momentum pT larger than a few GeV is above 95% over the whole region of pseudorapidity covered by the CMS muon system, abs(eta) < 2.4, while the probability to misidentify a hadron as a muon is well below 1%. The efficiency to trigger on single muons with pT above a few GeV is higher than 90% over the full eta range, and typically substantially better. The overall momentum scale is measured to a precision of 0.2% with muons from Z decays. The transverse momentum resolution varies from 1% to 6% depending on pseudorapidity for muons with pT below 100 GeV and, using cosmic rays, it is shown to be better than 10% in the central region up to pT = 1 TeV. Observed distributions of all quantities are well reproduced by the Monte Carlo simulation.Comment: Replaced with published version. Added journal reference and DO

    Performance of CMS muon reconstruction in pp collision events at sqrt(s) = 7 TeV