E A De Wolf

Université Libre de Bruxelles, Bruxelles, Brussels Capital Region, Belgium

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Publications (1234)

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    Full-text available · Article · Jan 2017
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    Full-text available · Article · Dec 2016
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    [Show abstract] [Hide abstract] ABSTRACT: A direct search for lepton flavour violating decays of the Higgs boson (H) in the H→eτ and H→eμ channels is described. The data sample used in the search was collected in proton–proton collisions at s=8 TeV with the CMS detector at the LHC and corresponds to an integrated luminosity of 19.7 fb−1. No evidence is found for lepton flavour violating decays in either final state. Upper limits on the branching fractions, B(H→eτ)<0.69% and B(H→eμ)<0.035%, are set at the 95% confidence level. The constraint set on B(H→eτ) is an order of magnitude more stringent than the existing indirect limits. The limits are used to constrain the corresponding flavour violating Yukawa couplings, absent in the standard model.
    Full-text available · Article · Oct 2016 · Physics Letters B
  • [Show abstract] [Hide abstract] ABSTRACT: Measurements are reported of the normalized differential cross sections for top quark pair production with respect to four kinematic event variables: the missing transverse energy; the scalar sum of the jet transverse momentum (pT); the scalar sum of the pT of all objects in the event; and the pT of leptonically decaying W bosons from top quark decays. The data sample, collected using the CMS detector at the LHC, consists of 5.0 fb−1 of proton-proton collisions at √s=7 TeV and 19.7 fb−1 at √s=8 TeV. Top quark pair events containing one electron or muon are selected. The results are presented after correcting for detector effects to allow direct comparison with theoretical predictions. No significant deviations from the predictions of several standard model event simulation generators are observed.
    Article · Sep 2016
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    G. Aad · B. Abbott · J. Abdallah · [...] · N. Woods
    [Show abstract] [Hide abstract] ABSTRACT: Combined ATLAS and CMS measurements of the Higgs boson production and decay rates, as well as constraints on its couplings to vector bosons and fermions, are presented. The combination is based on the analysis of five production processes, namely gluon fusion, vector boson fusion, and associated production with a W or a Z boson or a pair of top quarks, and of the six decay modes H → ZZ, W W , γγ, ττ, bb, and μμ. All results are reported assuming a value of 125.09 GeV for the Higgs boson mass, the result of the combined measurement by the ATLAS and CMS experiments. The analysis uses the CERN LHC proton-proton collision data recorded by the ATLAS and CMS experiments in 2011 and 2012, corresponding to integrated luminosities per experiment of approximately 5 fb−1 at \( \sqrt{s}=7 \) TeV and 20 fb−1 at \( \sqrt{s}=8 \) TeV. The Higgs boson production and decay rates measured by the two experiments are combined within the context of three generic parameterisations: two based on cross sections and branching fractions, and one on ratios of coupling modifiers. Several interpretations of the measurements with more model-dependent parameterisations are also given. The combined signal yield relative to the Standard Model prediction is measured to be 1.09 ± 0.11. The combined measurements lead to observed significances for the vector boson fusion production process and for the H → ττ decay of 5.4 and 5.5 standard deviations, respectively. The data are consistent with the Standard Model predictions for all parameterisations considered.
    Full-text available · Article · Aug 2016 · Journal of High Energy Physics
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    [Show abstract] [Hide abstract] ABSTRACT: A search for the resonant production of high-mass photon pairs is presented. The analysis is based on samples of proton-proton collision data collected by the CMS experiment at center-of-mass energies of 8 and 13 TeV, corresponding to integrated luminosities of 19.7 and 3.3 fb-1, respectively. The interpretation of the search results focuses on spin-0 and spin-2 resonances with masses between 0.5 and 4 TeV and with widths, relative to the mass, between 1.4×10-4 and 5.6×10-2. Limits are set on scalar resonances produced through gluon-gluon fusion, and on Randall-Sundrum gravitons. A modest excess of events compatible with a narrow resonance with a mass of about 750 GeV is observed. The local significance of the excess is approximately 3.4 standard deviations. The significance is reduced to 1.6 standard deviations once the effect of searching under multiple signal hypotheses is considered. More data are required to determine the origin of this excess.
    Full-text available · Article · Jul 2016 · Physical Review Letters
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    [Show abstract] [Hide abstract] ABSTRACT: A search for anomalous pseudoscalar couplings of the Higgs boson H to electroweak vector bosons V (=W or Z) in a sample of proton-proton collision events corresponding to an integrated luminosity of 18.9 fb−1at a center-of-mass energy of 8 TeVis presented. Events consistent with the topology of associated VH production, where the Higgs boson decays to a pair of bottom quarks and the vector boson decays leptonically, are analyzed. The consistency of data with a potential pseudoscalar contribution to the HVV interaction, expressed by the effective pseudoscalar cross section fractions fa3, is assessed by means of profile likelihood scans. Results are given for the VH channels alone and for a combined analysis of the VH and previously published H→VV channels. Under certain assumptions, fa3ZZ>0.0034 is excluded at 95% confidence level in the combination. Scenarios in which these assumptions are relaxed are also considered.
    Full-text available · Article · Jun 2016 · Physics Letters B
  • Working Paper · Jan 2016
  • [Show abstract] [Hide abstract] ABSTRACT: Results are reported from a search for R-parity violating supersymmetry in proton-proton collision events collected by the CMS experiment at a center-of-mass energy of $\sqrt{s} = 8$ TeV. The data sample corresponds to an integrated luminosity of 17.6 inverse femtobarns. This search assumes a minimal flavor violating model in which the lightest supersymmetric particle is a long-lived neutralino or gluino, leading to a signal with jets emanating from displaced vertices. In a sample of events with two displaced vertices, no excess yield above the expectation from standard model processes is observed, and limits are placed on the pair production cross section as a function of mass and lifetime of the neutralino or gluino. At 95% confidence level, the analysis excludes cross sections above approximately 1 fb for neutralinos or gluinos with mass between 400 and 1500 GeV and mean proper decay length between 1 and 30 mm. Assuming gluino pair production cross sections, gluino masses are excluded below 1 and 1.3 TeV for mean proper decay lengths of 300 micrometers and 1 mm, respectively, and below 1.4 TeV for the range 2-30 mm. The results are also applicable to other models in which long-lived particles decay into multijet final states.
    Working Paper · Jan 2016
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    [Show abstract] [Hide abstract] ABSTRACT: The nuclear modification factor ${R_{\mathrm{AA}}} $ and the azimuthal anisotropy coefficient ${v_{2}} $ of prompt and nonprompt (i.e. those from decays of b hadrons) $\mathrm{J}/\psi$ mesons, measured from PbPb and pp collisions at $\sqrt{s_{\mathrm{NN}}} = $ 2.76 TeV at the LHC, are reported. The results are presented in several event centrality intervals and several kinematic regions, for transverse momenta $p_{\mathrm{T}} > $ 6.5 GeV/$c$ and rapidity $| {y}
    Full-text available · Working Paper · Jan 2016
  • [Show abstract] [Hide abstract] ABSTRACT: This paper describes the search for a high-mass narrow-width scalar particle decaying into a Z boson and a photon. The analysis is performed using proton-proton collision data recorded with the CMS detector at the LHC at center-of-mass energies of 8 and 13 TeV, corresponding to integrated luminosities of 19.7 and 2.7 inverse femtobarns, respectively. The Z bosons are reconstructed from opposite-sign electron or muon pairs. No statistically significant deviation from the standard model predictions has been found in the 200-2000 GeV mass range. Upper limits at 95% confidence level have been derived on the product of the scalar particle production cross section and the branching fraction of the Z decaying into electrons or muons, which range from 280 to 20 fb for resonance masses between 200 and 2000 GeV.
    Working Paper · Jan 2016
  • [Show abstract] [Hide abstract] ABSTRACT: A search is presented for narrow resonances decaying to dijet final states in proton-proton collisions at $\sqrt{s} =$ 13 TeV using data corresponding to an integrated luminosity of 12.9 inverse femtobarns. The dijet mass spectrum is well described by a smooth parameterization and no significant evidence for the production of new particles is observed. Upper limits at 95% confidence level are reported on the production cross section for narrow resonances with masses above 0.6 TeV. In the context of specific models, the limits exclude string resonances with masses below 7.4 TeV, scalar diquarks below 6.9 TeV, axigluons and colorons below 5.5 TeV, excited quarks below 5.4 TeV, color-octet ascalars below 3.0 TeV, W bosons below 2.7 TeV, Z bosons below 2.1 TeV and between 2.3 and 2.6 TeV, and RS gravitons below 1.9 TeV. These extend previous limits in the dijet channel. Vector and axial-vector mediators in a simplified model of interactions between quarks and dark matter are excluded below 2.0 TeV. The first limits in the dijet channel on dark matter mediators are presented as functions of dark matter mass and are compared to the exclusions of dark matter in direct detection experiments.
    Working Paper · Jan 2016
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    [Show abstract] [Hide abstract] ABSTRACT: © 2015 CERN for the benefit of the CMS Collaboration. The first study of W boson production in pPb collisions is presented, for bosons decaying to a muon or electron, and a neutrino. The measurements are based on a data sample corresponding to an integrated luminosity of 34.6 nb-1 at a nucleon-nucleon centre-of-mass energy of √sNN = 5.02 TeV, collected by the CMS experiment. The W boson differential cross sections, lepton charge asymmetry, and forward-backward asymmetries are measured for leptons of transverse momentum exceeding 25 GeV/c, and as a function of the lepton pseudorapidity in the |ηlab|<2.4 range. Deviations from the expectations based on currently available parton distribution functions are observed, showing the need for including W boson data in nuclear parton distribution global fits.
    Full-text available · Article · Nov 2015 · Physics Letters B
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    [Show abstract] [Hide abstract] ABSTRACT: © 2015 CERN for the benefit of the CMS Collaboration. We present a measurement of the Z boson differential cross section in rapidity and transverse momentum using a data sample of pp collision events at a centre-of-mass energy s=8 TeV, corresponding to an integrated luminosity of 19.7 fb<sup>-1</sup>. The Z boson is identified via its decay to a pair of muons. The measurement provides a precision test of quantum chromodynamics over a large region of phase space. In addition, due to the small experimental uncertainties in the measurement the data has the potential to constrain the gluon parton distribution function in the kinematic regime important for Higgs boson production via gluon fusion. The results agree with the next-to-next-to-leading-order predictions computed with the fewz program. The results are also compared to the commonly used leading-order MadGraph and next-to-leading-order powheg generators.
    Full-text available · Article · Oct 2015 · Physics Letters B
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    [Show abstract] [Hide abstract] ABSTRACT: Results are presented from a search for particle dark matter (DM), extra dimensions, and unparticles using events containing a jet and an imbalance in transverse momentum. The data were collected by the CMS detector in proton-proton collisions at the LHC and correspond to an integrated luminosity of 19.7[Formula: see text]at a centre-of-mass energy of 8[Formula: see text]. The number of observed events is found to be consistent with the standard model prediction. Limits are placed on the DM-nucleon scattering cross section as a function of the DM particle mass for spin-dependent and spin-independent interactions. Limits are also placed on the scale parameter [Formula: see text] in the Arkani-Hamed, Dimopoulos, and Dvali (ADD) model of large extra dimensions, and on the unparticle model parameter [Formula: see text]. The constraints on ADD models and unparticles are the most stringent limits in this channel and those on the DM-nucleon scattering cross section are an improvement over previous collider results.
    Full-text available · Article · Jun 2015 · European Physical Journal C
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    [Show abstract] [Hide abstract] ABSTRACT: A search for new physics in proton-proton collisions having final states with an electron or muon and missing transverse energy is presented. The analysis uses data collected in 2012 with the CMS detector, at an LHC center-of-mass energy of 8 TeV, and corresponding to an integrated luminosity of 19.7 fb[superscript −1]. No significant deviation of the transverse mass distribution of the charged lepton-neutrino system from the standard model prediction is found. Mass exclusion limits of up to 3.28 TeV at 95% confidence level for a W′-boson with the same couplings as that of the standard model W-boson are determined. Results are also derived in the framework of split universal extra dimensions, and exclusion limits on Kaluza–Klein W[(2) over KK] states are found. The final state with large missing transverse energy also enables a search for dark matter production with a recoiling W-boson, with limits set on the mass and the production cross section of potential candidates. Finally, limits are established for a model including interference between a left-handed W′-boson and the standard model W-boson and for a compositeness model.
    Full-text available · Article · May 2015 · Physical Review D
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    [Show abstract] [Hide abstract] ABSTRACT: A measurement of the Higgs boson mass is presented based on the combined data samples of the ATLAS and CMS experiments at the CERN LHC in the H→γγ and H→ZZ→4ℓ decay channels. The results are obtained from a simultaneous fit to the reconstructed invariant mass peaks in the two channels and for the two experiments. The measured masses from the individual channels and the two experiments are found to be consistent among themselves. The combined measured mass of the Higgs boson is m_H=125.09±0.21 (stat)±0.11 (syst) GeV.
    Full-text available · Article · May 2015 · Physical Review Letters
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    [Show abstract] [Hide abstract] ABSTRACT: The double-differential cross sections of promptly produced J/ψ and ψ(2S) mesons are measured in pp collisions at sqrt[s]=7 TeV, as a function of transverse momentum p_{T} and absolute rapidity |y|. The analysis uses J/ψ and ψ(2S) dimuon samples collected by the CMS experiment, corresponding to integrated luminosities of 4.55 and 4.90 fb^{-1}, respectively. The results are based on a two-dimensional analysis of the dimuon invariant mass and decay length, and extend to p_{T}=120 and 100 GeV for the J/ψ and ψ(2S), respectively, when integrated over the interval |y|<1.2. The ratio of the ψ(2S) to J/ψ cross sections is also reported for |y|<1.2, over the range 10<p_{T}<100 GeV. These are the highest p_{T} values for which the cross sections and ratio have been measured.
    Full-text available · Article · May 2015 · Physical Review Letters
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    [Show abstract] [Hide abstract] ABSTRACT: The standard model of particle physics describes the fundamental particles and their interactions via the strong, electromagnetic and weak forces. It provides precise predictions for measurable quantities that can be tested experimentally. The probabilities, or branching fractions, of the strangeB meson (B0s ) andtheB0meson decaying into two oppositely charged muons (μ+ and μ-) are especially interesting because of their sensitivity to theories that extend the standard model. The standard model predicts that the B0s→μ+μ- and B0s→μ+μ- decays are very rare, with about four of the former occurring for every billion B0s mesons produced, and one of the latter occurring for every ten billion B0 mesons1. A difference in the observed branching fractions with respect to the predictions of the standard model would provide a direction in which the standard model should be extended. Before the Large Hadron Collider (LHC) at CERN2 started operating, no evidence for either decay mode had been found. Upper limits on the branching fractions were an order of magnitude above the standard model predictions. The CMS (CompactMuonSolenoid) andLHCb(LargeHadronCollider beauty) collaborations have performed a joint analysis of the data from proton'proton collisions that they collected in 2011 at a centre-ofmass energy of seven teraelectronvolts and in 2012 at eight teraelectronvolts. Here we report the first observation of the B0s→μ+μ- decay, with a statistical significance exceeding six standard deviations, and the best measurement so far of its branching fraction. Furthermore, we obtained evidence for the B0s→μ+μ- decay with a statistical significance of three standard deviations. Both measurements are statistically compatible with standard model predictions and allow stringent constraints to be placed on theories beyond the standardmodel. The LHCexperimentswill resume taking data in 2015, recording proton'proton collisions at a centre-of-mass energy of 13 teraelectronvolts, which will approximately double the production rates of B0s and B0 mesons and lead to further improvements in the precision of these crucial tests of the standard model.
    Full-text available · Article · May 2015 · Nature
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    [Show abstract] [Hide abstract] ABSTRACT: An inclusive search for supersymmetry in events with at least one b-tagged jet is performed using proton-proton collision data collected by the CMS experiment in 2012 at a center-of-mass energy of 8 TeV. The data set size corresponds to an integrated luminosity of 19.3 fb[superscript −1]. The two-dimensional distribution of the razor variables R[superscript 2] and M[subscript R] is studied in events with and without leptons. The data are found to be consistent with the expected background, which is modeled with an empirical function. Exclusion limits on supersymmetric particle masses at a 95% confidence level are derived in several simplified supersymmetric scenarios for several choices of the branching fractions. By combining the likelihoods of a search in events without leptons and a search that requires a single lepton (electron or muon), an improved bound on the top-squark mass is obtained. Assuming the lightest supersymmetric particle to be stable and weakly interacting, and to have a mass of 100 GeV, the branching-fraction-dependent (-independent) production of gluinos is excluded for gluino masses up to 1310 (1175) GeV. The corresponding limit for top-squark pair production is 730 (645) GeV.
    Full-text available · Article · May 2015

Publication Stats

25k Citations

Institutions

  • 2011-2013
    • Université Libre de Bruxelles
      • Department of Informatics
      Bruxelles, Brussels Capital Region, Belgium
  • 2010-2013
    • Yerevan Physics Institute
      Ayrivan, Yerevan, Armenia
  • 2001-2013
    • University of Antwerp
      • Department of Physics
      Antwerpen, Flanders, Belgium
  • 1988-2013
    • Vrije Universiteit Brussel
      • Accountancy, Auditing and Business Financing (ACCO)
      Bruxelles, Brussels Capital Region, Belgium
  • 2001-2011
    • CERN
      • Physics Department (PH)
      Genève, Geneva, Switzerland
  • 2003-2010
    • University of Freiburg
      • Faculty of Mathematics and Physics
      Freiburg, Baden-Württemberg, Germany
  • 2001-2009
    • University of Hamburg
      • Institut für Experimentalphysik
      Hamburg, Hamburg, Germany
  • 2005
    • University of Birmingham
      • School of Physics and Astronomy
      Birmingham, ENG, United Kingdom
  • 1987-2005
    • Radboud University Nijmegen
      Nymegen, Gelderland, Netherlands
  • 1995-1996
    • Humboldt-Universität zu Berlin
      Berlín, Berlin, Germany
  • 1994
    • Deutsches Elektronen-Synchrotron
      Hamburg, Hamburg, Germany
  • 1993
    • AGH University of Science and Technology in Kraków
      Cracovia, Lesser Poland Voivodeship, Poland