J.M. Butterworth

University of Granada, Granata, Andalusia, Spain

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Publications (707)

  • Source
    Dataset: RG1
    G. Aad · T. Abajyan · B. Abbott · [...] · S. Guindon
    Full-text Dataset · Aug 2016
  • Source
    M. Aaboud · G. Aad · B. Abbott · [...] · L. Zwalinski
    [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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    M. Aaboud · G. Aad · B. Abbott · [...] · L. Zwalinski
    [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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    G. Aad · B. Abbott · J. Abdallah · [...] · L. Zwalinski
    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
  • 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.
    Article · Aug 2016 · Journal of High Energy Physics
  • G. Aad · B. Abbott · J. Abdallah · [...] · ATLAS Collaboration
    [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
  • G. Aad · B. Abbott · J. Abdallah · [...] · L. Zwalinski
    [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.
    Article · Aug 2016 · Journal of High Energy Physics
  • [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.
    Article · Jul 2016 · Physics Letters B
  • [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.
    Article · Jul 2016 · Physics Letters B
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    G Aad · B Abbott · J Abdallah · [...] · O Rifki
    [Show abstract] [Hide abstract] ABSTRACT: A new search signature for excited leptons is explored. Excited muons are sought in the channel [${pp}\to \mu {\mu }^{* }\to \mu \mu \ {\rm{jet}}\;{\rm{jet}}$], assuming both the production and decay occur via a contact interaction. The analysis is based on 20.3 fb−1 of pp collision data at a centre-of-mass energy of [$\sqrt{s}\;=\;8\;{\rm{TeV}}$] taken with the ATLAS detector at the large hadron collider. No evidence of excited muons is found, and limits are set at the 95% confidence level on the cross section times branching ratio as a function of the excited-muon mass [${m}_{{\mu }^{* }}$]. For [${m}_{{\mu }^{* }}$] between 1.3 and 3.0 TeV, the upper limit on [$\sigma B({\mu }^{* }\to \mu q\bar{q}$]) is between 0.6 and 1 fb. Limits on [$\sigma B$] are converted to lower bounds on the compositeness scale Λ. In the limiting case [${\rm{\Lambda }}={m}_{{\mu }^{* }}$], excited muons with a mass below 2.8 TeV are excluded. With the same model assumptions, these limits at larger [${\mu }^{* }$] masses improve upon previous limits from traditional searches based on the gauge-mediated decay [${\mu }^{* }\to \mu \gamma $].
    Full-text Article · Jul 2016 · New Journal of Physics
  • [Show abstract] [Hide abstract] ABSTRACT: Event-shape observables measured using charged particles in inclusive Z-boson events are presented, using the electron and muon decay modes of the Z bosons. The measurements are based on an integrated luminosity of \(1.1~\mathrm{fb}^{-1}\) of proton–proton collisions recorded by the ATLAS detector at the LHC at a centre-of-mass energy \(\sqrt{s}=7\) \({\mathrm{TeV}}\). Charged-particle distributions, excluding the lepton–antilepton pair from the Z-boson decay, are measured in different ranges of transverse momentum of the Z boson. Distributions include multiplicity, scalar sum of transverse momenta, beam thrust, transverse thrust, spherocity, and \({\mathcal {F}}\)-parameter, which are in particular sensitive to properties of the underlying event at small values of the Z-boson transverse momentum. The measured observables are compared with predictions from Pythia 8, Sherpa, and Herwig 7. Typically, all three Monte Carlo generators provide predictions that are in better agreement with the data at high Z-boson transverse momenta than at low Z-boson transverse momenta, and for the observables that are less sensitive to the number of charged particles in the event.
    Article · Jul 2016 · European Physical Journal C
  • [Show abstract] [Hide abstract] ABSTRACT: This paper presents measurements of distributions of charged particles which are produced in proton–proton collisions at a centre-of-mass energy of \(\sqrt{s} = 8 \mathrm {\, TeV}\) and recorded by the ATLAS detector at the LHC. A special dataset recorded in 2012 with a small number of interactions per beam crossing (below 0.004) and corresponding to an integrated luminosity of 160 \(\upmu \mathrm{b}^{-1}\) was used. A minimum-bias trigger was utilised to select a data sample of more than 9 million collision events. The multiplicity, pseudorapidity, and transverse momentum distributions of charged particles are shown in different regions of kinematics and charged-particle multiplicity, including measurements of final states at high multiplicity. The results are corrected for detector effects and are compared to the predictions of various Monte Carlo event generator models which simulate the full hadronic final state.
    Article · Jul 2016 · European Physical Journal C
  • [Show abstract] [Hide abstract] ABSTRACT: A search for squarks and gluinos in final states containing hadronic jets, missing transverse momentum but no electrons or muons is presented. The data were recorded in 2015 by the ATLAS experiment in \(\sqrt{s}=13~{\mathrm{TeV}}\) proton–proton collisions at the Large Hadron Collider. No excess above the Standard Model background expectation was observed in 3.2 \(\mathrm{fb}^{-1}\) of analyzed data. Results are interpreted within simplified models that assume R-parity is conserved and the neutralino is the lightest supersymmetric particle. An exclusion limit at the 95 % confidence level on the mass of the gluino is set at 1.51 \({\mathrm{TeV}}\) for a simplified model incorporating only a gluino octet and the lightest neutralino, assuming the lightest neutralino is massless. For a simplified model involving the strong production of mass-degenerate first- and second-generation squarks, squark masses below 1.03 \({\mathrm{TeV}}\) are excluded for a massless lightest neutralino. These limits substantially extend the region of supersymmetric parameter space excluded by previous measurements with the ATLAS detector.
    Article · Jul 2016 · European Physical Journal C
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    [Show abstract] [Hide abstract] ABSTRACT: This paper presents a search for massive charged long-lived particles produced in pp collisions at s=13 TeV at the LHC using the ATLAS experiment. The data set used corresponds to an integrated luminosity of 3.2 fb-1. Many extensions of the Standard Model predict the existence of massive charged long-lived particles, such as R-hadrons. These massive particles are expected to be produced with a velocity significantly below the speed of light, and therefore to have a specific ionization higher than any Standard Model particle of unit charge at high momenta. The Pixel subsystem of the ATLAS detector is used to measure the ionization energy loss of reconstructed charged particles and to search for such highly ionizing particles. The search presented here has much greater sensitivity than a similar search performed using the ATLAS detector in the s=8 TeV data set, thanks to the increase in expected signal cross section due to the higher center-of-mass energy of collisions, to an upgraded detector with a new silicon layer close to the interaction point, and to analysis improvements. No significant deviation from Standard Model background expectations is observed, and lifetime-dependent upper limits on R-hadron production cross sections and masses are set. Gluino R-hadrons with lifetimes above 0.4 ns and decaying to qq plus a 100 GeV neutralino are excluded at the 95% confidence level, with lower mass limit ranging between 740 and 1590 GeV. In the case of stable R-hadrons the lower mass limit at the 95% confidence level is 1570 GeV.
    Full-text Article · Jun 2016
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    [Show abstract] [Hide abstract] ABSTRACT: Measurements of the and production cross sections (where ) in proton–proton collisions at are presented using data recorded by the ATLAS experiment at the Large Hadron Collider, corresponding to a total integrated luminosity of 81 pb−1. The total inclusive -boson production cross sections times the single-lepton-flavour branching ratios are and for and , respectively. The total inclusive _Z_-boson production cross section times leptonic branching ratio, within the invariant mass window , is . The , , and _Z_-boson production cross sections and cross-section ratios within a fiducial region defined by the detector acceptance are also measured. The cross-section ratios benefit from significant cancellation of experimental uncertainties, resulting in and . Theoretical predictions, based on calculations accurate to next-to-next-to-leading order for quantum chromodynamics and to next-to-leading order for electroweak processes and which employ different parton distribution function sets, are compared to these measurements.
    Full-text Article · Jun 2016 · Physics Letters B
  • [Show abstract] [Hide abstract] ABSTRACT: Charged Higgs bosons produced in association with a single top quark and decaying via H±→τν are searched for with the ATLAS experiment at the LHC, using proton–proton collision data at s=13 TeV corresponding to an integrated luminosity of 3.2 fb−1. The final state is characterised by the presence of a hadronic τ decay and missing transverse momentum, as well as a hadronically decaying top quark, resulting in the absence of high-transverse-momentum electrons and muons. The data are found to be consistent with the expected background from Standard Model processes. A statistical analysis leads to 95% confidence-level upper limits on the production cross section times branching fraction, σ(pp→[b]tH±)×BR(H±→τν), between 1.9 pb and 15 fb, for charged Higgs boson masses ranging from 200 to 2000 GeV. The exclusion limits for this search surpass those obtained with the proton–proton collision data recorded at s=8 TeV.
    Article · Jun 2016 · Physics Letters B
  • [Show abstract] [Hide abstract] ABSTRACT: The production of Z bosons with one or two isolated high-energy photons is studied using pp collisions at s=8 TeV. The analyses use a data sample with an integrated luminosity of 20.3 fb-1 collected by the ATLAS detector during the 2012 LHC data taking. The Zγ and Zγγ production cross sections are measured with leptonic (e+e-, μ+μ-, νν) decays of the Z boson, in extended fiducial regions defined in terms of the lepton and photon acceptance. They are then compared to cross-section predictions from the Standard Model, where the sources of the photons are radiation off initial-state quarks and radiative Z-boson decay to charged leptons, and from fragmentation of final-state quarks and gluons into photons. The yields of events with photon transverse energy ET>250 GeV from +-γ events and with ET>400 GeV from ννγ events are used to search for anomalous triple gauge-boson couplings ZZγ and Zγγ. The yields of events with diphoton invariant mass mγγ>200 GeV from +-γγ events and with mγγ>300 GeV from ννγγ events are used to search for anomalous quartic gauge-boson couplings ZZγγ and Zγγγ. No deviations from Standard Model predictions are observed and limits are placed on parameters used to describe anomalous triple and quartic gauge-boson couplings.
    Article · Jun 2016
  • [Show abstract] [Hide abstract] ABSTRACT: The production of D*±, D± and Ds± charmed mesons has been measured with the ATLAS detector in pp collisions at s=7 TeV at the LHC, using data corresponding to an integrated luminosity of 280 nb-1. The charmed mesons have been reconstructed in the range of transverse momentum 3.5<pT(D)<100 GeV and pseudorapidity |η(D)|<2.1. The differential cross sections as a function of transverse momentum and pseudorapidity were measured for D*± and D± production. The next-to-leading-order QCD predictions are consistent with the data in the visible kinematic region within the large theoretical uncertainties. Using the visible D cross sections and an extrapolation to the full kinematic phase space, the strangeness-suppression factor in charm fragmentation, the fraction of charged non-strange D mesons produced in a vector state, and the total cross section of charm production at s√=7 TeV were derived.
    Article · Jun 2016

Publication Stats

15k Citations

Institutions

  • 2015
    • University of Granada
      Granata, Andalusia, Spain
  • 2013
    • University of Belgrade
      • Institute of Physics
      Beograd, Central Serbia, Serbia
  • 1993-2013
    • University of Freiburg
      • Faculty of Mathematics and Physics
      Freiburg, Lower Saxony, Germany
  • 1996-2011
    • University College London
      • Department of Physics and Astronomy
      London, ENG, United Kingdom
  • 2010
    • University of Surrey
      • Department of Physics
      Guilford, England, United Kingdom
  • 2009
    • Tokyo Institute of Technology
      • Department of Physics
      Edo, Tōkyō, Japan
    • University of Bonn
      Bonn, North Rhine-Westphalia, Germany
    • Ludwig-Maximilians-University of Munich
      München, Bavaria, Germany
  • 2008
    • Argonne National Laboratory
      • Division of Physics
      Lemont, Illinois, United States
    • University of London
      Londinium, England, United Kingdom
    • University of Warsaw
      • Institute of Experimental Physics
      Warszawa, Masovian Voivodeship, Poland
  • 2005
    • Humboldt-Universität zu Berlin
      Berlín, Berlin, Germany
  • 2000-2004
    • University of Hamburg
      • Institute of Applied Physics
      Hamburg, Hamburg, Germany
  • 1993-1996
    • Pennsylvania State University
      • Department of Physics
      University Park, Maryland, United States