3,008 research outputs found

    Proton Losses in the LHC due to Momentum Cleaning at Top Energy

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    A set of the simulations of the momentum cleaning during collisions at top energy is done. The results for the proton losses at the collimators and at the other limiting apertures are presented and discussed

    Beam-induced Background Simulations for the CMS Experiment at the LHC

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    Beam-induced background comes from interactions of the beam and beam halo particles with either the residual gas in the vacuum chamber of accelerator or the collimators that define the beam aperture. Beam-induced processes can potentially be a significant source of background for physics analyses at the LHC. This contribution describes the simulation software environment used for this part of the CMS experiment activity and recent beam-induced background simulation results for the Phase-2 CMS operation design

    Combined search for the quarks of a sequential fourth generation

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    Results are presented from a search for a fourth generation of quarks produced singly or in pairs in a data set corresponding to an integrated luminosity of 5 inverse femtobarns recorded by the CMS experiment at the LHC in 2011. A novel strategy has been developed for a combined search for quarks of the up and down type in decay channels with at least one isolated muon or electron. Limits on the mass of the fourth-generation quarks and the relevant Cabibbo-Kobayashi-Maskawa matrix elements are derived in the context of a simple extension of the standard model with a sequential fourth generation of fermions. The existence of mass-degenerate fourth-generation quarks with masses below 685 GeV is excluded at 95% confidence level for minimal off-diagonal mixing between the third- and the fourth-generation quarks. With a mass difference of 25 GeV between the quark masses, the obtained limit on the masses of the fourth-generation quarks shifts by about +/- 20 GeV. These results significantly reduce the allowed parameter space for a fourth generation of fermions.Comment: Replaced with published version. Added journal reference and DO

    Measurement of the t t-bar production cross section in the dilepton channel in pp collisions at sqrt(s) = 7 TeV