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Sökning: LAR1:uu > Bocchetta Simona

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1.
  • Aaboud, M, et al. (författare)
  • Combination of the Searches for Pair-Produced Vectorlike Partners of the Third-Generation Quarks at s =13 TeV with the ATLAS Detector
  • 2018
  • Ingår i: Physical Review Letters. - : American Physical Society. - 1079-7114 .- 0031-9007. ; 121:21
  • Tidskriftsartikel (refereegranskat)abstract
    • A combination of the searches for pair-produced vectorlike partners of the top and bottom quarks in various decay channels (T→Zt/Wb/Ht, B→Zb/Wt/Hb) is performed using 36.1 fb-1 of pp collision data at s=13 TeV with the ATLAS detector at the Large Hadron Collider. The observed data are found to be in good agreement with the standard model background prediction in all individual searches. Therefore, combined 95% confidence-level upper limits are set on the production cross section for a range of vectorlike quark scenarios, significantly improving upon the reach of the individual searches. Model-independent limits are set assuming the vectorlike quarks decay to standard model particles. A singlet T is excluded for masses below 1.31 TeV and a singlet B is excluded for masses below 1.22 TeV. Assuming a weak isospin (T,B) doublet and |VTb|â‰|VtB|, T and B masses below 1.37 TeV are excluded. © 2018 CERN. for the ATLAS Collaboration.
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2.
  • Aaboud, M, et al. (författare)
  • Comparison between simulated and observed LHC beam backgrounds in the ATLAS experiment at Ebeam=4 TeV
  • 2018
  • Ingår i: Journal of Instrumentation. - : IOP Publishing. - 1748-0221. ; 13:12
  • Tidskriftsartikel (refereegranskat)abstract
    • Results of dedicated Monte Carlo simulations of beam-induced background (BIB) in the ATLAS experiment at the Large Hadron Collider (LHC) are presented and compared with data recorded in 2012. During normal physics operation this background arises mainly from scattering of the 4 TeV protons on residual gas in the beam pipe. Methods of reconstructing the BIB signals in the ATLAS detector, developed and implemented in the simulation chain based on the \textsc{Fluka} Monte Carlo simulation package, are described. The interaction rates are determined from the residual gas pressure distribution in the LHC ring in order to set an absolute scale on the predicted rates of BIB so that they can be compared quantitatively with data. Through these comparisons the origins of the BIB leading to different observables in the ATLAS detectors are analysed. The level of agreement between simulation results and BIB measurements by ATLAS in 2012 demonstrates that a good understanding of the origin of BIB has been reached. © 2018 CERN for the benefit of the ATLAS collaboration.
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3.
  • Aaboud, M, et al. (författare)
  • Dark matter interpretations of ATLAS searches for the electroweak production of supersymmetric particles in √s=8 TeV proton-proton collisions
  • 2016
  • Ingår i: Journal of High Energy Physics. - : Springer. - 1029-8479 .- 1126-6708. ; 2016:9
  • Tidskriftsartikel (refereegranskat)abstract
    • A selection of searches by the ATLAS experiment at the LHC for the electroweak production of SUSY particles are used to study their impact on the constraints on dark matter candidates. The searches use 20 fb−1 of proton-proton collision data at s=8 TeV. A likelihood-driven scan of a five-dimensional effective model focusing on the gaugino-higgsino and Higgs sector of the phenomenological minimal supersymmetric Standard Model is performed. This scan uses data from direct dark matter detection experiments, the relic dark matter density and precision flavour physics results. Further constraints from the ATLAS Higgs mass measurement and SUSY searches at LEP are also applied. A subset of models selected from this scan are used to assess the impact of the selected ATLAS searches in this five-dimensional parameter space. These ATLAS searches substantially impact those models for which the mass m(χ˜10) of the lightest neutralino is less than 65 GeV, excluding 86% of such models. The searches have limited impact on models with larger m(χ˜10) due to either heavy electroweakinos or compressed mass spectra where the mass splittings between the produced particles and the lightest supersymmetric particle is small.[Figure not available: see fulltext.] © 2016, The Author(s).
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4.
  • Aaboud, M, et al. (författare)
  • Evidence for light-by-light scattering in heavy-ion collisions with the ATLAS detector at the LHC
  • 2017
  • Ingår i: Nature Physics. - : Nature Publishing Group. - 1745-2473 .- 1745-2481. ; 13:9, s. 852-858
  • Tidskriftsartikel (refereegranskat)abstract
    • Light-by-light scattering (γγ → γγ) is a quantum-mechanical process that is forbidden in the classical theory of electrodynamics. This reaction is accessible at the Large Hadron Collider thanks to the large electromagnetic field strengths generated by ultra-relativistic colliding lead ions. Using 480 μ1 of lead-lead collision data recorded at a centre-of-mass energy per nucleon pair of 5.02 TeV by the ATLAS detector, here we report evidence for light-by-light scattering. A total of 13 candidate events were observed with an expected background of 2.6 ± 0.7 events. After background subtraction and analysis corrections, the fiducial cross-section of the process Pb + Pb (γγ) → Pb(∗) + Pb(∗)γγ,for photon transverse energy ET > 3GeV, photon absolute pseudorapidity |η| <2.4, diphoton invariant mass greater than 6GeV, diphoton transverse momentum lower than 2GeV and diphoton acoplanarity below 0.01, is measured to be 70 ± 24 (stat.) ±17 (syst.) nb, which is in agreement with the standard model predictions. © 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.
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5.
  • Aaboud, M, et al. (författare)
  • High-ET isolated-photon plus jets production in pp collisions at s=8 TeV with the ATLAS detector
  • 2017
  • Ingår i: Nuclear Physics B. - : North-Holland. - 0550-3213 .- 1873-1562. ; 918, s. 257-316
  • Tidskriftsartikel (refereegranskat)abstract
    • The dynamics of isolated-photon plus one-, two- and three-jet production in pp collisions at a centre-of-mass energy of 8 TeV are studied with the ATLAS detector at the LHC using a data set with an integrated luminosity of 20.2 fb−1. Measurements of isolated-photon plus jets cross sections are presented as functions of the photon and jet transverse momenta. The cross sections as functions of the azimuthal angle between the photon and the jets, the azimuthal angle between the jets, the photon–jet invariant mass and the scattering angle in the photon–jet centre-of-mass system are presented. The pattern of QCD radiation around the photon and the leading jet is investigated by measuring jet production in an annular region centred on each object; enhancements are observed around the leading jet with respect to the photon in the directions towards the beams. The experimental measurements are compared to several different theoretical calculations, and overall a good description of the data is found. © 2017 The Author(s)
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6.
  • Aaboud, M, et al. (författare)
  • In situ calibration of large-radius jet energy and mass in 13 TeV proton–proton collisions with the ATLAS detector
  • 2019
  • Ingår i: European Physical Journal C. - : Springer. - 1434-6044 .- 1434-6052. ; 79:2
  • Tidskriftsartikel (refereegranskat)abstract
    • The response of the ATLAS detector to large-radius jets is measured in situ using 36.2 fb - 1 of s=13 TeV proton–proton collisions provided by the LHC and recorded by the ATLAS experiment during 2015 and 2016. The jet energy scale is measured in events where the jet recoils against a reference object, which can be either a calibrated photon, a reconstructed Z boson, or a system of well-measured small-radius jets. The jet energy resolution and a calibration of forward jets are derived using dijet balance measurements. The jet mass response is measured with two methods: using mass peaks formed by W bosons and top quarks with large transverse momenta and by comparing the jet mass measured using the energy deposited in the calorimeter with that using the momenta of charged-particle tracks. The transverse momentum and mass responses in simulations are found to be about 2–3% higher than in data. This difference is adjusted for with a correction factor. The results of the different methods are combined to yield a calibration over a large range of transverse momenta (p T ). The precision of the relative jet energy scale is 1–2% for 200GeV
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7.
  • Aaboud, M, et al. (författare)
  • Jet energy scale measurements and their systematic uncertainties in proton-proton collisions at s =13 TeV with the ATLAS detector
  • 2017
  • Ingår i: Physical Review D. - : American Physical Society. - 1550-2368. ; 96:7:7
  • Tidskriftsartikel (refereegranskat)abstract
    • Jet energy scale measurements and their systematic uncertainties are reported for jets measured with the ATLAS detector using proton-proton collision data with a center-of-mass energy of s=13 TeV, corresponding to an integrated luminosity of 3.2 fb-1 collected during 2015 at the LHC. Jets are reconstructed from energy deposits forming topological clusters of calorimeter cells, using the anti-kt algorithm with radius parameter R=0.4. Jets are calibrated with a series of simulation-based corrections and in situ techniques. In situ techniques exploit the transverse momentum balance between a jet and a reference object such as a photon, Z boson, or multijet system for jets with 200.8) is derived from dijet pT balance measurements. For jets of pT=80 GeV, the additional uncertainty for the forward jet calibration reaches its largest value of about 2% in the range |η|>3.5 and in a narrow slice of 2.2
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8.
  • Aaboud, M, et al. (författare)
  • Measurement of differential cross-sections of a single top quark produced in association with a W boson at √s=13TeV with ATLAS
  • 2018
  • Ingår i: European Physical Journal C. - : Springer. - 1434-6044 .- 1434-6052. ; 78:3
  • Tidskriftsartikel (refereegranskat)abstract
    • The differential cross-section for the production of a W boson in association with a top quark is measured for several particle-level observables. The measurements are performed using 36.1fb-1 of pp collision data collected with the ATLAS detector at the LHC in 2015 and 2016. Differential cross-sections are measured in a fiducial phase space defined by the presence of two charged leptons and exactly one jet matched to a b-hadron, and are normalised with the fiducial cross-section. Results are found to be in good agreement with predictions from several Monte Carlo event generators. © 2018, CERN for the benefit of the ATLAS collaboration.
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9.
  • Aaboud, M, et al. (författare)
  • Measurement of jet activity produced in top-quark events with an electron, a muon and two b-tagged jets in the final state in pp collisions at √s=13 TeV with the ATLAS detector
  • 2017
  • Ingår i: European Physical Journal C. - : Springer. - 1434-6044 .- 1434-6052. ; 77:4
  • Tidskriftsartikel (refereegranskat)abstract
    • Measurements of jet activity in top-quark pair events produced in proton–proton collisions are presented, using 3.2 fb- 1of pp collision data at a centre-of-mass energy of 13 TeV collected by the ATLAS experiment at the Large Hadron Collider. Events are chosen by requiring an opposite-charge eμ pair and two b-tagged jets in the final state. The normalised differential cross-sections of top-quark pair production are presented as functions of additional-jet multiplicity and transverse momentum, pT. The fraction of signal events that do not contain additional jet activity in a given rapidity region, the gap fraction, is measured as a function of the pTthreshold for additional jets, and is also presented for different invariant mass regions of the eμbb¯ system. All measurements are corrected for detector effects and presented as particle-level distributions compared to predictions with different theoretical approaches for QCD radiation. While the kinematics of the jets from top-quark decays are described well, the generators show differing levels of agreement with the measurements of observables that depend on the production of additional jets. © 2017, CERN for the benefit of the ATLAS collaboration.
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10.
  • Aaboud, M, et al. (författare)
  • Measurement of the cross-section for producing a W boson in association with a single top quark in pp collisions at √s=13 TeV with ATLAS
  • 2018
  • Ingår i: Journal of High Energy Physics. - : Springer. - 1029-8479 .- 1126-6708. ; 2018:1
  • Tidskriftsartikel (refereegranskat)abstract
    • The inclusive cross-section for the associated production of a W boson and top quark is measured using data from proton-proton collisions at s=13 TeV. The dataset corresponds to an integrated luminosity of 3.2 fb−1, and was collected in 2015 by the ATLAS detector at the Large Hadron Collider at CERN. Events are selected requiring two opposite sign isolated leptons and at least one jet; they are separated into signal and control regions based on their jet multiplicity and the number of jets that are identified as containing b hadrons. The W t signal is then separated from the tt¯ background using boosted decision tree discriminants in two regions. The cross-section is extracted by fitting templates to the data distributions, and is measured to be σW t = 94 ± 10(stat.)− 22 + 28(syst.) ± 2(lumi.) pb. The measured value is in good agreement with the SM prediction of σtheory = 71.7±1.8 (scale)± 3.4 (PDF) pb [1].[Figure not available: see fulltext.]. © 2018, The Author(s).
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