24 research outputs found

    Search for dark matter particles in proton-proton collisions at √s=8 TeV using the razor variables

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    A search for dark matter particles directly produced in proton-proton collisions recorded by the CMS experiment at the LHC is presented. The data correspond to an integrated luminosity of 18.8 fb−1, at a center-of-mass energy of 8 TeV. The event selection requires at least two jets and no isolated leptons. The razor variables are used to quantify the transverse momentum balance in the jet momenta. The study is performed separately for events with and without jets originating from b quarks. The observed yields are consistent with the expected backgrounds and, depending on the nature of the production mechanism, dark matter production at the LHC is excluded at 90% confidence level for a mediator mass scale Λ below 1 TeV. The use of razor variables yields results that complement those previously published

    Search for massive resonances decaying into WW, WZ or ZZ bosons in proton-proton collisions at √s=13TeV

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    Measurements of the differential cross sections of the production of Z + jets and γ + jets and of Z boson emission collinear with a jet in pp collisions at s \sqrt{s} = 13 TeV

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    Measurements of the differential cross sections of Z + jets and γ + jets production, and their ratio, are presented as a function of the boson transverse momentum. Measurements are also presented of the angular distribution between the Z boson and the closest jet. The analysis is based on pp collisions at a center-of-mass energy of 13 TeV corresponding to an integrated luminosity of 35.9 fb−1 recorded by the CMS experiment at the LHC. The results, corrected for detector effects, are compared with various theoretical predictions. In general, the predictions at higher orders in perturbation theory show better agreement with the measurements. This work provides the first measurement of the ratio of the differential cross sections of Z + jets and γ + jets production at 13 TeV, as well as the first direct measurement of Z bosons emitted collinearly with a jet

    Search for associated production of a Z boson with a single top quark and for tZ flavour-changing interactions in pp collisions at √s=8 TeV

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    A search for the production of a single top quark in association with a Z boson is presented, both to identify the expected standard model process and to search for flavour-changing neutral current interactions. The data sample corresponds to an integrated luminosity of 19.7 fb−1 recorded by the CMS experiment at the LHC in proton-proton collisions at s√=8 TeV. Final states with three leptons (electrons or muons) and at least one jet are investigated. An events yield compatible with tZq standard model production is observed, and the corresponding cross section is measured to be σ(pp → tZq → ℓνbℓ+ℓ−q) = 10− 7+ 8 fb with a significance of 2.4 standard deviations. No presence of flavour-changing neutral current production of tZq is observed. Exclusion limits at 95% confidence level on the branching fractions of a top quark decaying to a Z boson and an up or a charm quark are found to be ℬ(t → Zu) < 0.022% and ℬ(t → Zc) < 0.049%

    Search for dark matter particles in proton-proton collisions at √s=8 TeV using the razor variables

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    Measurement of electroweak production of a W boson and two forward jets in proton-proton collisions at √s=8 TeV

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    A measurement is presented of the cross section for the electroweak production of a W boson in association with two jets in proton-proton collisions at a center-of-mass energy of 8 TeV. The data set was collected with the CMS detector and corresponds to an integrated luminosity of 19.3 fb−1 . The measured fiducial cross section for W bosons decaying to electrons or muons and for pT j1 > 60 GeV, pT j2 > 50 GeV, |η j | < 4.7, and mjj > 1000 GeV is 0.42 ± 0.04 (stat) ± 0.09 (syst) ± 0.01 (lumi) pb. This result is consistent with the standard model leading-order prediction of 0.50 ± 0.02 (scale) ± 0.02 (PDF) pb obtained with MadGraph5 amc@nlo 2.1 interfaced to pythia 6.4. This is the first cross section measurement for this process

    Measurement of electroweak production of a W boson and two forward jets in proton-proton collisions at √s=8 Tev

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    A measurement is presented of the cross section for the electroweak production of a W boson in association with two jets in proton-proton collisions at a center-of-mass energy of 8 TeV. The data set was collected with the CMS detector and corresponds to an integrated luminosity of 19.3 fb−1. The measured fiducial cross section for W bosons decaying to electrons or muons and for pTj1> 60 GeV, pTj2> 50 GeV, |ηj| 1000 GeV is 0.42 ± 0.04 (stat) ± 0.09 (syst) ± 0.01 (lumi) pb. This result is consistent with the standard model leading-order prediction of 0.50 ± 0.02 (scale) ± 0.02 (PDF) pb obtained with MadGraph5_amc@nlo 2.1 interfaced to pythia 6.4. This is the first cross section measurement for this process

    Search for direct pair production of scalar top quarks in the single- and dilepton channels in proton-proton collisions at √s=8 TeV

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    Results are reported from a search for the top squark et1, the lighter of the two supersymmetric partners of the top quark. The data sample corresponds to 19.7 fb−1 of proton-proton collisions at √ s = 8 TeV collected with the CMS detector at the LHC. The search targets et1 → bχe ± 1 and et1 → t (∗)χe 0 1 decay modes, where χe ± 1 and χe 0 1 are the lightest chargino and neutralino, respectively. The reconstructed final state consists of jets, b jets, missing transverse energy, and either one or two leptons. Leading backgrounds are determined from data. No significant excess in data is observed above the expectation from standard model processes. The results exclude a region of the two-dimensional plane of possible et1 and χe 0 1 masses. The highest excluded et1 and χe 0 1 masses are about 700 GeV and 250 GeV, respectively

    Erratum to: Search for direct pair production of scalar top quarks in the single- and dilepton channels in proton-proton collisions at √s = 8 TeV

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    Measurement of electroweak production of a W boson and two forward jets in proton-proton collisions at s = 8 s=8 \sqrt{s}=8 TeV

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