H Pernegger

University of Granada, Granata, Andalusia, Spain

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Publications (796)

  • Source
    M. Aaboud · G. Aad · B. Abbott · [...] · L. Zwalinski
    [Show abstract] [Hide abstract] ABSTRACT: A search is conducted for both resonant and non-resonant high-mass new phenomena in dielectron and dimuon final states. The search uses 3.2fb−1 of proton–proton collision data, collected at s=13TeV by the ATLAS experiment at the LHC in 2015. The dilepton invariant mass is used as the discriminating variable. No significant deviation from the Standard Model prediction is observed; therefore limits are set on the signal model parameters of interest at 95% credibility level. Upper limits are set on the cross-section times branching ratio for resonances decaying to dileptons, and the limits are converted into lower limits on the resonance mass, ranging between 2.74 TeV and 3.36 TeV, depending on the model. Lower limits on the ℓℓqq contact interaction scale are set between 16.7 TeV and 25.2 TeV, also depending on the model.
    Full-text Article · Oct 2016 · Physics Letters B
  • Source
    M Aaboud · G Aad · B Abbott · [...] · A Redelbach
    [Show abstract] [Hide abstract] ABSTRACT: An inclusive search for a new-physics signature of lepton-jet resonances has been performed by the ATLAS experiment. Scalar leptoquarks, pair-produced in pp collisions at [$\sqrt{s}$] = 13 TeV at the large hadron collider, have been considered. An integrated luminosity of 3.2 fb⁻¹, corresponding to the full 2015 dataset was used. First (second) generation leptoquarks were sought in events with two electrons (muons) and two or more jets. The observed event yield in each channel is consistent with Standard Model background expectations. The observed (expected) lower limits on the leptoquark mass at 95% confidence level are 1100 and 1050 GeV (1160 and 1040 GeV) for first and second generation leptoquarks, respectively, assuming a branching ratio into a charged lepton and a quark of 100%. Upper limits on the aforementioned branching ratio are also given as a function of leptoquark mass. Compared with the results of earlier ATLAS searches, the sensitivity is increased for leptoquark masses above 860 GeV, and the observed exclusion limits confirm and extend the published results.
    Full-text Article · Sep 2016 · New Journal of Physics
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    M. Aaboud · G. Aad · B. Abbott · [...] · L. Zwalinski
    [Show abstract] [Hide abstract] ABSTRACT: The production of W±Z events in proton–proton collisions at a centre-of-mass energy of 13 TeV is measured with the ATLAS detector at the LHC. The collected data correspond to an integrated luminosity of 3.2 fb−1. The W±Z candidates are reconstructed using leptonic decays of the gauge bosons into electrons or muons. The measured inclusive cross section in the detector fiducial region for leptonic decay modes is σW±Z→ℓ′νℓℓfid.=63.2±3.2(stat.)±2.6(sys.)±1.5(lumi.) fb. In comparison, the next-to-leading-order Standard Model prediction is 53.4−2.8+3.6 fb. The extrapolation of the measurement from the fiducial to the total phase space yields σW±Ztot.=50.6±2.6(stat.)±2.0(sys.)±0.9(th.)±1.2(lumi.) pb, in agreement with a recent next-to-next-to-leading-order calculation of 48.2−1.0+1.1 pb. The cross section as a function of jet multiplicity is also measured, together with the charge-dependent W+Z and W−Z cross sections and their ratio.
    Full-text Article · Sep 2016 · Physics Letters B
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    M. Aaboud · G. Aad · B. Abbott · [...] · L. Zwalinski
    Full-text Article · Sep 2016
  • G. Aad · B. Abbott · J. Abdallah · [...] · L. Zwalinski
    [Show abstract] [Hide abstract] ABSTRACT: The production of W boson pairs in proton-proton collisions at \( \sqrt{s}=8 \) TeV is studied using data corresponding to 20.3 fb−1 of integrated luminosity collected by the ATLAS detector during 2012 at the CERN Large Hadron Collider. The W bosons are reconstructed using their leptonic decays into electrons or muons and neutrinos. Events with reconstructed jets are not included in the candidate event sample. A total of 6636 WW candidate events are observed. Measurements are performed in fiducial regions closely approximating the detector acceptance. The integrated measurement is corrected for all acceptance effects and for the W branching fractions to leptons in order to obtain the total WW production cross section, which is found to be 71.1 ± 1.1(stat) − 5.0+ 5.7(syst) ± 1.4(lumi) pb. This agrees with the next-to-next-to-leading-order Standard Model prediction of 63. 2− 1.4+ 1.6(scale) ± 1.2(PDF) pb. Fiducial differential cross sections are measured as a function of each of six kinematic variables. The distribution of the transverse momentum of the leading lepton is used to set limits on anomalous triple-gauge-boson couplings.
    Article · Sep 2016 · Journal of High Energy Physics
  • Source
    M. Aaboud · G. Aad · B. Abbott · [...] · L. Zwalinski
    [Show abstract] [Hide abstract] ABSTRACT: Searches for new resonances decaying into two photons in the ATLAS experiment at the CERN Large Hadron Collider are described. The analysis is based on proton-proton collision data corresponding to an integrated luminosity of 3.2 fb−1 at \( \sqrt{s}=13 \) TeV recorded in 2015. Two searches are performed, one targeted at a spin-2 particle of mass larger than 500 GeV, using Randall-Sundrum graviton states as a benchmark model, and one optimized for a spin-0 particle of mass larger than 200 GeV. Varying both the mass and the decay width, the most significant deviation from the background-only hypothesis is observed at a diphoton invariant mass around 750 GeV with local significances of 3.8 and 3.9 standard deviations in the searches optimized for a spin-2 and spin-0 particle, respectively. The global significances are estimated to be 2.1 standard deviations for both analyses. The consistency between the data collected at 13 TeV and 8 TeV is also evaluated. Limits on the production cross section times branching ratio to two photons for the two resonance types are reported.
    Full-text Article · Sep 2016 · Journal of High Energy Physics
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    Full-text Article · Aug 2016
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    [Show abstract] [Hide abstract] ABSTRACT: The top quark mass is measured in the tt¯→dilepton channel (lepton=e,μ) using ATLAS data recorded in the year 2012 at the LHC. The data were taken at a proton–proton centre-of-mass energy of s=8 TeV and correspond to an integrated luminosity of about 20.2 fb−1. Exploiting the template method, and using the distribution of invariant masses of lepton–b-jet pairs, the top quark mass is measured to be mtop=172.99±0.41 (stat)±0.74 (syst) GeV, with a total uncertainty of 0.84 GeV. Finally, a combination with previous ATLAS mtop measurements from s=7 TeV data in the tt¯→dilepton and tt¯→lepton+jets channels results in mtop=172.84±0.34 (stat)±0.61 (syst) GeV, with a total uncertainty of 0.70 GeV.
    Full-text Article · Aug 2016 · Physics Letters B
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: This paper describes a measurement of the inclusive top quark pair production cross-section (σtt¯) with a data sample of 3.2fb−1 of proton–proton collisions at a centre-of-mass energy of s=13TeV, collected in 2015 by the ATLAS detector at the LHC. This measurement uses events with an opposite-charge electron–muon pair in the final state. Jets containing b-quarks are tagged using an algorithm based on track impact parameters and reconstructed secondary vertices. The numbers of events with exactly one and exactly two b-tagged jets are counted and used to determine simultaneously σtt¯ and the efficiency to reconstruct and b-tag a jet from a top quark decay, thereby minimising the associated systematic uncertainties. The cross-section is measured to be:σtt¯=818±8(stat)±27(syst)±19(lumi)±12(beam) pb, where the four uncertainties arise from data statistics, experimental and theoretical systematic effects, the integrated luminosity and the LHC beam energy, giving a total relative uncertainty of 4.4%. The result is consistent with theoretical QCD calculations at next-to-next-to-leading order. A fiducial measurement corresponding to the experimental acceptance of the leptons is also presented.
    Full-text Article · Aug 2016 · Physics Letters B
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    [Show abstract] [Hide abstract] ABSTRACT: A measurement of the total pp cross section at the LHC at s=8 TeV is presented. An integrated luminosity of 500 μb−1 was accumulated in a special run with high-β⋆ beam optics to measure the differential elastic cross section as a function of the Mandelstam momentum transfer variable t. The measurement is performed with the ALFA sub-detector of ATLAS. Using a fit to the differential elastic cross section in the −t range from 0.014 GeV2 to 0.1 GeV2 to extrapolate t→0, the total cross section, σtot(pp→X), is measured via the optical theorem to beσtot(pp→X)=96.07±0.18(stat.)±0.85(exp.)±0.31(extr.)mb, where the first error is statistical, the second accounts for all experimental systematic uncertainties and the last is related to uncertainties in the extrapolation t→0. In addition, the slope of the exponential function describing the elastic cross section at small t is determined to be B=19.74±0.05(stat.)±0.23(syst.)GeV−2.
    Full-text Article · Aug 2016 · Physics Letters B
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    [Show abstract] [Hide abstract] ABSTRACT: A search for supersymmetry involving the pair production of gluinos decaying via third-generation squarks to the lightest neutralino (χ10) is reported. It uses an LHC proton-proton data set at a center-of-mass energy s=13 TeV with an integrated luminosity of 3.2 fb-1 collected with the ATLAS detector in 2015. The signal is searched for in events containing several energetic jets, of which at least three must be identified as b jets, large missing transverse momentum, and, potentially, isolated electrons or muons. Large-radius jets with a high mass are also used to identify highly boosted top quarks. No excess is found above the predicted background. For χ10 masses below approximately 700 GeV, gluino masses of less than 1.78 TeV and 1.76 TeV are excluded at the 95% C.L. in simplified models of the pair production of gluinos decaying via sbottom and stop, respectively. These results significantly extend the exclusion limits obtained with the s=8 TeV data set.
    Full-text Article · Aug 2016
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    [Show abstract] [Hide abstract] ABSTRACT: A measurement of the cross section for the inclusive production of isolated prompt photons in proton-proton collisions at a centre-of-mass energy of \( \sqrt{s}=8 \) TeV is presented. The measurement covers the pseudorapidity ranges |η γ | < 1.37 and 1.56 ≤ |η γ | < 2.37 in the transverse energy range 25 < E T γ < 1500 GeV. The results are based on an integrated luminosity of 20.2 fb−1, recorded by the ATLAS detector at the LHC. Photon candidates are identified by combining information from the calorimeters and the inner tracker. The background is subtracted using a data-driven technique, based on the observed calorimeter shower-shape variables and the deposition of hadronic energy in a narrow cone around the photon candidate. The measured cross sections are compared with leading-order and next-to-leading order perturbative QCD calculations and are found to be in a good agreement over ten orders of magnitude.
    Full-text Article · Aug 2016 · Journal of High Energy Physics
  • [Show abstract] [Hide abstract] ABSTRACT: This paper presents a measurement of the double-differential cross section for the Drell-Yan Z/γ∗ → ℓ+ℓ− and photon-induced γγ → ℓ+ℓ− processes where ℓ is an electron or muon. The measurement is performed for invariant masses of the lepton pairs, mℓℓ, between 116 GeV and 1500 GeV using a sample of 20.3 fb−1 of pp collisions data at centre-of-mass energy of \( \sqrt{s}=8 \) TeV collected by the ATLAS detector at the LHC in 2012. The data are presented double differentially in invariant mass and absolute dilepton rapidity as well as in invariant mass and absolute pseudorapidity separation of the lepton pair. The single-differential cross section as a function of mℓℓ is also reported. The electron and muon channel measurements are combined and a total experimental precision of better than 1% is achieved at low mℓℓ. A comparison to next-to-next-to-leading order perturbative QCD predictions using several recent parton distribution functions and including next-to-leading order electroweak effects indicates the potential of the data to constrain parton distribution functions. In particular, a large impact of the data on the photon PDF is demonstrated.
    Article · Aug 2016 · Journal of High Energy Physics
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    G. Aad · B. Abbott · J. Abdallah · [...] · L. Zwalinski
    [Show abstract] [Hide abstract] ABSTRACT: A measurement of the Bs0 decay parameters in the Bs0 → J/ψϕ channel using an integrated luminosity of 14.3 fb−1 collected by the ATLAS detector from 8 TeV pp collisions at the LHC is presented. The measured parameters include the CP -violating phase ϕs, the decay width Γs and the width difference between the mass eigenstates ΔΓs. The values measured for the physical parameters are statistically combined with those from 4.9 fb−1 of 7 TeV data, leading to the following: $$ \begin{array}{l}{\phi}_s=-0.090\pm 0.078\left(\mathrm{stat}.\right)\pm 0.041\left(\mathrm{syst}.\right)\mathrm{rad}\\ {}\varDelta {\varGamma}_s=0.085\pm 0.011\left(\mathrm{stat}.\right)\pm 0.007\left(\mathrm{syst}.\right){\mathrm{ps}}^{-1}\\ {}{\varGamma}_s=0.675\pm 0.003\left(\mathrm{stat}.\right)\pm 0.003\left(\mathrm{syst}.\right){\mathrm{ps}}^{-1}.\end{array} $$In the analysis the parameter ΔΓs is constrained to be positive. Results for ϕs and ΔΓs are also presented as 68% and 95% likelihood contours in the ϕs-ΔΓs plane. Also measured in this decay channel are the transversity amplitudes and corresponding strong phases. All measurements are in agreement with the Standard Model predictions.
    Full-text Article · Aug 2016 · Journal of High Energy Physics
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    G. Aad · B. Abbott · J. Abdallah · [...] · L. Zwalinski
    [Show abstract] [Hide abstract] ABSTRACT: The angular distributions of Drell-Yan charged lepton pairs in the vicinity of the Z-boson mass peak probe the underlying QCD dynamics of Z-boson production. This paper presents a measurement of the complete set of angular coefficients A0−7 describing these distributions in the Z-boson Collins-Soper frame. The data analysed correspond to 20.3 fb−1 of pp collisions at \( \sqrt{s}=8 \) TeV, collected by the ATLAS detector at the CERN LHC. The measurements are compared to the most precise fixed-order calculations currently available \( \left(\mathcal{O}\left({\alpha}_{\mathrm{s}}^2\right)\right) \) and with theoretical predictions embedded in Monte Carlo generators. The measurements are precise enough to probe QCD corrections beyond the formal accuracy of these calculations and to provide discrimination between different parton-shower models. A significant deviation from the \( \left(\mathcal{O}\left({\alpha}_{\mathrm{s}}^2\right)\right) \) predictions is observed for A0 − A2. Evidence is found for non-zero A5,6,7, consistent with expectations.
    Full-text Article · Aug 2016 · Journal of High Energy Physics
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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 Article · Aug 2016 · Journal of High Energy Physics
  • [Show abstract] [Hide abstract] ABSTRACT: A search for singly produced vector-like Q quarks, where Q can be either a T quark with charge \(+2/3\) or a Y quark with charge \(-4/3\), is performed in proton–proton collisions recorded with the ATLAS detector at the LHC. The dataset corresponds to an integrated luminosity of 20.3 fb\(^{-1}\) and was produced with a centre-of-mass energy of \(\sqrt{s}=8\) TeV. This analysis targets \(Q \rightarrow Wb\) decays where the W boson decays leptonically. A veto on massive large-radius jets is used to reject the dominant \(t\bar{t}\) background. The reconstructed Q-candidate mass, ranging from 0.4 to 1.2 TeV, is used in the search to discriminate signal from background processes. No significant deviation from the Standard Model expectation is observed, and limits are set on the \(Q \rightarrow Wb\) cross-section times branching ratio. The results are also interpreted as limits on the QWb coupling and the mixing with the Standard Model sector for a singlet T quark or a Y quark from a doublet. T quarks with masses below 0.95 TeV are excluded at 95 % confidence level, assuming a unit coupling and a BR\((T\rightarrow Wb) = 0.5\), whereas the expected limit is 1.10 TeV.
    Article · Aug 2016 · European Physical Journal C
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    [Show abstract] [Hide abstract] ABSTRACT: This paper describes a measurement of fiducial and differential cross sections of gluon-fusion Higgs boson production in the H → W W∗→ eνμν channel, using 20.3 fb−1 of proton-proton collision data. The data were produced at a centre-of-mass energy of \( \sqrt{s}=8 \) TeV at the CERN Large Hadron Collider and recorded by the ATLAS detector in 2012. Cross sections are measured from the observed H→ W W∗→ eνμν signal yield in categories distinguished by the number of associated jets. The total cross section is measured in a fiducial region defined by the kinematic properties of the charged leptons and neutrinos. Differential cross sections are reported as a function of the number of jets, the Higgs boson transverse momentum, the dilepton rapidity, and the transverse momentum of the leading jet. The jet-veto efficiency, or fraction of events with no jets above a given transverse momentum threshold, is also reported. All measurements are compared to QCD predictions from Monte Carlo generators and fixed-order calculations, and are in agreement with the Standard Model predictions.
    Full-text Article · Aug 2016 · Journal of High Energy Physics
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    [Show abstract] [Hide abstract] ABSTRACT: A search for heavy long-lived charged R-hadrons is reported using a data sample corresponding to 3.2 fb−1of proton–proton collisions at s=13 TeV collected by the ATLAS experiment at the Large Hadron Collider at CERN. The search is based on observables related to large ionisation losses and slow propagation velocities, which are signatures of heavy charged particles travelling significantly slower than the speed of light. No significant deviations from the expected background are observed. Upper limits at 95% confidence level are provided on the production cross section of long-lived R-hadrons in the mass range from 600 GeV to 2000 GeV and gluino, bottom and top squark masses are excluded up to 1580 GeV, 805 GeV and 890 GeV, respectively.
    Full-text Article · Jul 2016 · Physics Letters B
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    [Show abstract] [Hide abstract] ABSTRACT: A search for physics beyond the Standard Model, in final states with at least one high transverse momentum charged lepton (electron or muon) and two additional high transverse momentum leptons or jets, is performed using 3.2 fb−1 of proton–proton collision data recorded by the ATLAS detector at the Large Hadron Collider in 2015 at s=13 TeV. The upper end of the distribution of the scalar sum of the transverse momenta of leptons and jets is sensitive to the production of high-mass objects. No excess of events beyond Standard Model predictions is observed. Exclusion limits are set for models of microscopic black holes with two to six extra dimensions.
    Full-text Article · Jul 2016 · Physics Letters B

Publication Stats

13k Citations

Institutions

  • 2015
    • University of Granada
      Granata, Andalusia, Spain
  • 2003-2014
    • CERN
      • Physics Department (PH)
      Genève, Geneva, Switzerland
    • University of Hamburg
      Hamburg, Hamburg, Germany
  • 2010-2013
    • University of Freiburg
      • Faculty of Mathematics and Physics
      Freiburg, Lower Saxony, Germany
  • 2011
    • Università di Pisa
      • Department of Physics "E.Fermi"
      Pisa, Tuscany, Italy
  • 2008
    • The University of Manchester
      • School of Physics and Astronomy
      Manchester, ENG, United Kingdom
  • 2005
    • University of Melbourne
      • School of Physics
      Melbourne, Victoria, Australia
  • 1998-2005
    • Massachusetts Institute of Technology
      • Laboratory for Nuclear Science
      Cambridge, Massachusetts, United States
    • University of Padova
      Padua, Veneto, Italy
  • 2002-2004
    • Argonne National Laboratory
      • Division of Physics
      Lemont, Illinois, United States
    • University of Rochester
      Rochester, New York, United States
  • 1993-1998
    • University of Milan
      • Department of Physics
      Milano, Lombardy, Italy
  • 1996
    • Università degli Studi di Trieste
      • Department of Physics
      Trieste, Friuli Venezia Giulia, Italy
  • 1994-1996
    • Austrian Academy of Sciences
      • Institute for High Energy Physics
      Wien, Vienna, Austria
    • Institut für Hochenergiephysik Wien
      Wien, Vienna, Austria
    • Bergische Universität Wuppertal
      Wuppertal, North Rhine-Westphalia, Germany
    • Uppsala University
      • Department of Radiology, Oncology and Radiation Science
      Uppsala, Uppsala, Sweden
    • University of Rome Tor Vergata
      • Dipartimento di Fisica
      Roma, Latium, Italy