6 research outputs found

    Search for the associated production of the Higgs boson with a top-quark pair

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    A search for the standard model Higgs boson produced in association with a top-quark pair t t ¯ H (tt¯H) is presented, using data samples corresponding to integrated luminosities of up to 5.1 fb −1 and 19.7 fb −1 collected in pp collisions at center-of-mass energies of 7 TeV and 8 TeV respectively. The search is based on the following signatures of the Higgs boson decay: H → hadrons, H → photons, and H → leptons. The results are characterized by an observed t t ¯ H tt¯H signal strength relative to the standard model cross section, μ = σ/σ SM ,under the assumption that the Higgs boson decays as expected in the standard model. The best fit value is μ = 2.8 ± 1.0 for a Higgs boson mass of 125.6 GeV

    Measurement of prompt Jψ\psi pair production in pp collisions at \sqrt s = 7 Tev

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    Production of prompt J/ ψ meson pairs in proton-proton collisions at 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 into μ + 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 | 6.5 GeV/ c ; 1.2 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%

    Measurements of the t(t)Overbar charge asymmetry using the dilepton decay channel in pp collisions at root s=7 TeV

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    The tt¯ charge asymmetry in proton-proton collisions at s√ = 7 TeV is measured using the dilepton decay channel (ee, e μ , or μμ ). The data correspond to a total integrated luminosity of 5.0 fb −1 , collected by the CMS experiment at the LHC. The tt and lepton charge asymmetries, defined as the differences in absolute values of the rapidities between the reconstructed top quarks and antiquarks and of the pseudorapidities between the positive and negative leptons, respectively, are measured to be A C = −0 . 010 ± 0 . 017 (stat . ) ± 0 . 008 (syst . ) and AlepC = 0 . 009 ± 0 . 010 (stat . ) ± 0 . 006 (syst . ). The lepton charge asymmetry is also measured as a function of the invariant mass, rapidity, and transverse momentum of the tt¯ system. All measurements are consistent with the expectations of the standard model

    Potato Shoot Tip Cryopreservation. A Review

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    Potato is one of the most important crops worldwide. Genetic resources of potato (Solanum tuberosum L. ssp. tuberosum) and related cultivated species are conserved through storage of tubers, in vitro plants and in cryopreservation. Cryopreservation, storage in or above liquid nitrogen, is the best option to maintain vegetatively propagated plants in the long term. The present review gives comprehensive information about various cryopreservation techniques for potato published from 1977 until the present. It discusses factors that affect the process and success of cryopreservation, such as donor culture conditions, preculture, cooling, warming and post-culture treatments. Studies are presented that analyse the histological and ultrastructural changes after different cryopreservation steps and the morphological pathways during regeneration of plants after rewarming. The maintenance of genetic stability in potato after cryopreservation has also been demonstrated by various phenotypic and molecular methods.The first thermal analyses on potato shoot tips are presented using differential scanning calorimetry to analyse the state of water during cooling and warming. Biochemical analyses of different compounds, such as soluble sugars and proteins, have been performed to understand and improve existing cryogenic methods. Potato is an example where successful virus elimination has been obtained via cryopreservation of shoot tips (cryotherapy). There are already cryopreserved collections of potato shoot tips in Germany, Peru, Czech Republic, South Korea and USA, but additional experiments on fundamental aspects of potato cryopreservation will help to improve understanding of the different cryopreservation methods, start new collections in other countries and also build up existing cryocollections of potato

    Search for the associated production of the Higgs boson with a top-quark pair

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    2014
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