1,238 research outputs found

    Single top Production at sqrt(s) =7 TeV

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    The production of single top quarks occurs via three processes: t-channel, s-channel and tW associated production. The LHC experiments have observed single top production via t-channel at 7 TeV and measured its cross section, providing a measurement of |Vtb| with an uncertainty at the 10% level. Studies are in place to observe tW associated production with a sensitivity close to 3sigma and the first limits on the production cross section for s-channel are set. Other studies based on single top topologies, like flavor changing neutral currents (FCNC) are also being performed.Comment: Proceedings from the talk "Single top Production at sqrt(s)=7 TeV presented during the QCD session of the Rencontres de Moriond 2012, 4 page

    Recent CMS results in top and Higgs physics

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    After the Higgs boson discovery in 2012, the investigation of its properties and compatibility with the standard model predictions is central to the physics program of the LHC experiments. Likewise, the study of the top quark is still relevant at the LHC, more than two decades after its discovery at the Tevatron. Top quarks and Higgs bosons are produced at the LHC on a large scale and share a deep connection based on the large mass of the top quark. Both particles provide an excellent laboratory in which to search for new physics: the measurement of their properties tests the foundations of the standard model; and they feature prominently in a variety of exotic signals. The coupling of the Higgs boson to the top quark, a fundamental standard model parameter, can only be measured directly in processes where the two particles are produced together. The production of a Higgs boson together with one or two top quarks is also sensitive to several exciting new physics effects. A brief overview of the current experimental status of top quark and Higgs boson physics is presented using results from the CMS Collaboration.Comment: Updated version of the Wine & Cheese: Joint Experimental-Theoretical Physics Seminar 'Recent CMS results in top and Higgs physics' given at Fermilab, 20 November 2015. To appear in Mod. Phys. Lett.

    Discovery Potential for the SM Higgs Boson in the H -> WW* -> 2l2nu channel at LHC

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    A prospective analysis for the search of the Standard Model (SM) Higgs boson with the CMS detector is presented in the context of the early LHC data. The aim is to establish an analysis strategy for inclusive production of the Higgs boson decaying in WW* pairs in the context of the early LHC data. Higgs mass region between 120-200 GeV, in which this signature was proposed as highly sensitive, has been studied. The W decays into lnu are considered, where l stands for e or mu. The final states are characterized by two, opposite-sign, high transverse momentum leptons, missing energy, carried out by the undetected neutrinos, and little jet activity. This study uses Monte Carlo (MC) events with full detector simulation, including limited calibration and alignment precision as expected at the LHC startup. Sets of sequential cuts are applied to each of the three topologies, in order to isolate a signal which exceeds the tt and continuum WW backgrounds. Alternatively, an artificial neural network multi-variate analysis technique is used.Comment: Poster at ICHEP08, Philadelphia, USA, July 2008. 3 pages, 3 eps figure

    Study of double parton scattering using W + 2-jet events in proton-proton collisions at √s = 7 TeV

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    Double parton scattering is investigated in proton-proton collisions at √s = 7 TeV where the final state includes a W boson, which decays into a muon and a neutrino, and two jets. The data sample corresponds to an integrated luminosity of 5 fb−1, collected with the CMS detector at the LHC. Observables sensitive to double parton scattering are investigated after being corrected for detector effects and selection efficiencies. The fraction of W + 2-jet events due to double parton scattering is measured to be 0.055 ± 0.002 (stat.) ± 0.014 (syst.). The effective cross section, σeff, characterizing the effective transverse area of hard partonic interactions in collisions between protons is measured to be 20.7 ± 0.8 (stat.) ± 6.6 (syst.)mb

    Study of the production of charged pions, kaons, and protons in pPb collisions at √sNN = 5.02TeV

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    Spectra of identified charged hadrons are meas√ ured in pPb collisions with the CMS detector at the LHC at sNN = 5.02 TeV. Charged pions, kaons, and protons in the transverse-momentum range pT ≈ 0.1–1.7 GeV/c and laboratory rapidity |y| \u3c 1 are identified via their energy loss in the silicon tracker. The average pT increases with particle mass and the charged multiplicity of the event. The increase of the average pT with charged multiplicity is greater for heavier hadrons. Comparisons to Monte Carlo event generators reveal that Epos Lhc, which incorporates additional hydrodynamic evolution of the created system, is able to reproduce most of the data features, unlike Hijing and Ampt. The pT spectra and integrated yields are also compared to those measured in pp and PbPb collisions at various energies. The average transverse momentum and particle ratio measurements indicate that particle production at LHC energies is strongly correlated with event particle multiplicity

    Measurement of the triple-differential cross section for photon + jets production in proton-proton collisions at √s = 7 TeV

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    A measurement of the triple-differential cross section, d3σ/(dpTϒ dɳϒ dɳjet), in photon+jets final states using a data sample from proton-proton collisions at√s = 7TeV is presented. This sample corresponds to an integrated luminosity of 2.14 fb−1 collected bythe CMS detector at the LHC. Photons and jets are reconstructed within a pseudorapidity range of |ɳ| \u3c 2.5, and are required to have transverse momenta in the range 40 \u3c pjetT \u3c 300 GeV and pjetT \u3e 30 GeV, respectively. The measurements are compared to theoretical predictions from the sherpa leading-order QCD Monte Carlo event generator and the next-to-leading-order perturbative QCD calculation from jetphox. The predictions are found to be consistent with the data over most of the examined kinematic region

    Search for pair production of excited top quarks in the lepton+jets final state

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    A search is performed for pair-produced spin-3/2 excited top quarks (t*t¯*), each decaying to a top quark and a gluon. The search uses data collected with the CMS detector from pp collisions at a center-of-mass energy of √s = 8TeV, selecting events that have a single isolated muon or electron, an imbalance in transverse momentum, and at least six jets, of which one must be compatible with originating from the fragmentation of a b quark. The data, corresponding to an integrated luminosity of 19.5 fb−1, show no significant excess over standard model predictions, and provide a lower limit of 803 GeV at 95% confidence on the mass of the spin-3/2 t* quark in an extension of the Randall-Sundrum model, assuming a 100% branching fraction of its decay into a top quark and a gluon. This is the first search for a spin-3/2 excited top quark performed at the LHC

    Measurement of Higgs boson production and properties in the WW decay channel with leptonic final states

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    A search for the standard model Higgs boson decaying to a W-boson pair at the LHC is reported. The event sample corresponds to an integrated luminosity of 4.9 fb−1 and 19.4 fb−1 collected with the CMS detector in pp collisions at √ s = 7 and 8TeV, respectively. The Higgs boson candidates are selected in events with two or three charged leptons. An excess of events above background is observed, consistent with the expectation from the standard model Higgs boson with a mass of around 125 GeV. The probability to observe an excess equal or larger than the one seen, under the background-only hypothesis, corresponds to a significance of 4.3 standard deviations for mH = 125.6 GeV. The observed signal cross section times the branching fraction to WW for mH = 125.6 GeV is 0.72+0.20−0.18 times the standard model expectation. The spin-parity JP = 0+ hypothesis is favored against a narrow resonance with JP = 2+ or JP = 0− that decays to a W-boson pair. This result provides strong evidence for a Higgs-like boson decaying to a W-boson pair

    Event generator tunes obtained from underlying event and multiparton scattering measurements

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    New sets of parameters (“tunes”) for the underlying-event (UE) modelling of the PYTHIA8, PYTHIA6 and HERWIG++ MonteCarlo event generators are constructed using different parton distribution functions. Combined fits to CMS UE proton–proton (pp) data at √s = 7 TeV and to UE proton–antiproton (pp) data from the CDF experiment at lower √s, are used to study the UE models and constrain their parameters, providing thereby improved predictions for proton–proton collisions at 13 TeV. In addition, it is investigated whether the values of the parameters obtained from fits to UE observables are consistent with the values determined from fitting observables sensitive to double-parton scattering processes. Finally, comparisons are presented of the UE tunes to “minimum bias” (MB) events, multijet, and Drell– Yan (qq → Z/γ*→lepton-antilepton+jets) observables at 7 and 8 TeV, as well as predictions for MB and UE observables at 13 TeV
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