Bertrand Laforge

Publications (236) View all

• Source

  Available from: Cesare Bacci

  Article: Measurement of Z Boson Production in Pb-Pb Collisions at sqrt[s_{NN}]=2.76 TeV with the ATLAS Detector.

  G Aad, T Abajyan, B Abbott, J Abdallah, S Abdel Khalek, A A Abdelalim, O Abdinov, R Aben, B Abi, M Abolins, [......], S Zimmermann, M Ziolkowski, R Zitoun, L Zivković, V V Zmouchko, G Zobernig, A Zoccoli, M Zur Nedden, V Zutshi, L Zwalinski
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  ABSTRACT: The ATLAS experiment has observed 1995 Z boson candidates in data corresponding to 0.15 nb^{-1} of integrated luminosity obtained in the 2011 LHC Pb+Pb run at sqrt[s_{NN}]=2.76 TeV. The Z bosons are reconstructed via dielectron and dimuon decay channels, with a background contamination of less than 3%. Results from the two channels are consistent and are combined. Within the statistical and systematic uncertainties, the per-event Z boson yield is proportional to the number of binary collisions estimated by the Glauber model. The elliptic anisotropy of the azimuthal distribution of the Z boson with respect to the event plane is found to be consistent with zero.
  Physical Review Letters 01/2013; 110(2):022301. · 7.37 Impact Factor
• Article: Search for Dark Matter Candidates and Large Extra Dimensions in Events with a Photon and Missing Transverse Momentum in pp Collision Data at sqrt[s]=7 TeV with the ATLAS Detector.

  G Aad, T Abajyan, B Abbott, J Abdallah, S Abdel Khalek, A A Abdelalim, O Abdinov, R Aben, B Abi, M Abolins, [......], S Zimmermann, M Ziolkowski, R Zitoun, L Zivković, V V Zmouchko, G Zobernig, A Zoccoli, M Zur Nedden, V Zutshi, L Zwalinski
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  ABSTRACT: Results of a search for new phenomena in events with an energetic photon and large missing transverse momentum in proton-proton collisions at sqrt[s]=7 TeV are reported. Data collected by the ATLAS experiment at the LHC corresponding to an integrated luminosity of 4.6 fb^{-1} are used. Good agreement is observed between the data and the standard model predictions. The results are translated into exclusion limits on models with large extra spatial dimensions and on pair production of weakly interacting dark matter candidates.
  Physical Review Letters 01/2013; 110(1):011802. · 7.37 Impact Factor
• Article: Search for Magnetic Monopoles in sqrt[s]=7 TeV pp Collisions with the ATLAS Detector.

  G Aad, T Abajyan, B Abbott, J Abdallah, S Abdel Khalek, A A Abdelalim, O Abdinov, R Aben, B Abi, M Abolins, [......], S Zimmermann, M Ziolkowski, R Zitoun, L Zivković, V V Zmouchko, G Zobernig, A Zoccoli, M Zur Nedden, V Zutshi, L Zwalinski
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  ABSTRACT: This Letter presents a search for magnetic monopoles with the ATLAS detector at the CERN Large Hadron Collider using an integrated luminosity of 2.0 fb^{-1} of pp collisions recorded at a center-of-mass energy of sqrt[s]=7 TeV. No event is found in the signal region, leading to an upper limit on the production cross section at 95% confidence level of 1.6/ϵ fb for Dirac magnetic monopoles with the minimum unit magnetic charge and with mass between 200 GeV and 1500 GeV, where ϵ is the monopole reconstruction efficiency. The efficiency ϵ is high and uniform in the fiducial region given by pseudorapidity |η|<1.37 and transverse kinetic energy 600-700<E^{kin}sin⁡θ<1400 GeV. The minimum value of 700 GeV is for monopoles of mass 200 GeV, whereas the minimum value of 600 GeV is applicable for higher mass monopoles. Therefore, the upper limit on the production cross section at 95% confidence level is 2 fb in this fiducial region. Assuming the kinematic distributions from Drell-Yan pair production of spin-1/2 Dirac magnetic monopoles, the efficiency is in the range 1%-10%, leading to an upper limit on the cross section at 95% confidence level that varies from 145 fb to 16 fb for monopoles with mass between 200 GeV and 1200 GeV. This limit is weaker than the fiducial limit because most of these monopoles lie outside the fiducial region.
  Physical Review Letters 12/2012; 109(26):261803. · 7.37 Impact Factor
• Source

  Available from: Till Eifert

  Article: Search for Direct Top Squark Pair Production in Final States with One Isolated Lepton, Jets, and Missing Transverse Momentum in sqrt[s]=7  TeV pp Collisions Using 4.7  fb^{-1} of ATLAS Data.

  G Aad, T Abajyan, B Abbott, J Abdallah, S Abdel Khalek, A A Abdelalim, O Abdinov, R Aben, B Abi, M Abolins, [......], S Zimmermann, M Ziolkowski, R Zitoun, L Zivković, V V Zmouchko, G Zobernig, A Zoccoli, M Zur Nedden, V Zutshi, L Zwalinski
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  ABSTRACT: A search is presented for direct top squark pair production in final states with one isolated electron or muon, jets, and missing transverse momentum in proton-proton collisions at sqrt[s]=7  TeV. The measurement is based on 4.7  fb^{-1} of data collected with the ATLAS detector at the LHC. Each top squark is assumed to decay to a top quark and the lightest supersymmetric particle (LSP). The data are found to be consistent with standard model expectations. Top squark masses between 230 GeV and 440 GeV are excluded with 95% confidence for massless LSPs, and top squark masses around 400 GeV are excluded for LSP masses up to 125 GeV.
  Physical Review Letters 11/2012; 109(21):211803. · 7.37 Impact Factor
• Article: Search for a Supersymmetric Partner to the Top Quark in Final States with Jets and Missing Transverse Momentum at sqrt[s]=7  TeV with the ATLAS Detector.

  G Aad, T Abajyan, B Abbott, J Abdallah, S Abdel Khalek, A A Abdelalim, O Abdinov, R Aben, B Abi, M Abolins, [......], S Zimmermann, M Ziolkowski, R Zitoun, L Zivković, V V Zmouchko, G Zobernig, A Zoccoli, M Zur Nedden, V Zutshi, L Zwalinski
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  ABSTRACT: A search for direct pair production of supersymmetric top squarks (t[over ˜]_{1}) is presented, assuming the t[over ˜]_{1} decays into a top quark and the lightest supersymmetric particle, χ[over ˜]_{1}^{0}, and that both top quarks decay to purely hadronic final states. A total of 16 (4) events are observed compared to a predicted standard model background of 13.5_{-3.6}^{+3.7}(4.4_{-1.3}^{+1.7}) events in two signal regions based on ∫Ldt=4.7  fb^{-1} of pp collision data taken at sqrt[s]=7  TeV with the ATLAS detector at the LHC. An exclusion region in the t[over ˜]_{1} versus χ[over ˜]_{1}^{0} mass plane is evaluated: 370<m_{t[over ˜]_{1}}<465  GeV is excluded for m_{χ[over ˜]_{1}^{0}}∼0  GeV while m_{t[over ˜]_{1}}=445  GeV is excluded for m_{χ[over ˜]_{1}^{0}}≤50  GeV.
  Physical Review Letters 11/2012; 109(21):211802. · 7.37 Impact Factor