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1.
  • Aad, G., et al. (författare)
  • Search for invisible particles produced in association with single-top-quarks in proton-proton collisions at [Formula: see text] with the ATLAS detector.
  • 2015
  • Ingår i: European Physical Journal C. Particles and Fields. - Springer. - 1434-6044. ; 75:2
  • Tidskriftsartikel (refereegranskat)abstract
    • A search for the production of single-top-quarks in association with missing energy is performed in proton-proton collisions at a centre-of-mass energy of [Formula: see text] with the ATLAS experiment at the large hadron collider using data collected in 2012, corresponding to an integrated luminosity of [Formula: see text] fb[Formula: see text]. In this search, the [Formula: see text] boson from the top quark is required to decay into an electron or a muon and a neutrino. No deviation from the standard model prediction is observed, and upper limits are set on the production cross-section for resonant and non-resonant production of an invisible exotic state in association with a right-handed top quark. In the case of resonant production, for a spin-[Formula: see text] resonance with a mass of [Formula: see text] GeV, an effective coupling strength above [Formula: see text] is excluded at 95[Formula: see text] confidence level for the top quark and an invisible spin-[Formula: see text] state with mass between [Formula: see text] and [Formula: see text] GeV. In the case of non-resonant production, an effective coupling strength above [Formula: see text] is excluded at 95[Formula: see text] confidence level for the top quark and an invisible spin-[Formula: see text] state with mass between [Formula: see text] and [Formula: see text] GeV.
2.
  • Abulaiti, Yiming, et al. (författare)
  • Measurement of the t(t)over-bar production cross-section as a function of jet multiplicity and jet transverse momentum in 7 TeV proton-proton collisions with the ATLAS detector
  • 2015
  • Ingår i: Journal of High Energy Physics. - Springer. - 1029-8479. ; :1, s. 1-67
  • Tidskriftsartikel (refereegranskat)abstract
    • The t (t) over bar production cross-section dependence on jet multiplicity and jet transverse momentum is reported for proton-proton collisions at a centre-of-mass energy of 7 TeV in the single-lepton channel. The data were collected with the ATLAS detector at the CERN Large Hadron Collider and comprise the full 2011 data sample corresponding to an integrated luminosity of 4.6 fb(-1). Differential cross-sections are presented as a function of the jet multiplicity for up to eight jets using jet transverse momentum thresholds of 25, 40, 60, and 80 GeV, and as a function of jet transverse momentum up to the fifth jet. The results are shown after background subtraction and corrections for all known detector effects, within a kinematic range closely matched to the experimental acceptance. Several QCD-based Monte Carlo models are compared with the results. Sensitivity to the parton shower modelling is found at the higher jet multiplicities, at high transverse momentum of the leading jet and in the transverse momentum spectrum of the fifth leading jet. The MC@NLO+HERWIG MC is found to predict too few events at higher jet multiplicities.
3.
  • Aad, G., et al. (författare)
  • Identification and energy calibration of hadronically decaying tau leptons with the ATLAS experiment in pp collisions at root s=8 TeV
  • 2015
  • Ingår i: European Physical Journal C. Particles and Fields. - Springer. - 1434-6044. ; 75:7
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper describes the trigger and offline reconstruction, identification and energy calibration algorithms for hadronic decays of tau leptons employed for the data collected from pp collisions in 2012 with the ATLAS detector at the LHC center-of-mass energy root s = 8 TeV. The performance of these algorithms is measured in most cases with Z decays to tau leptons using the full 2012 dataset, corresponding to an integrated luminosity of 20.3 fb(-1). An uncertainty on the offline reconstructed tau energy scale of 2-4%, depending on transverse energy and pseudorapidity, is achieved using two independent methods. The offline tau identification efficiency is measured with a precision of 2.5% for hadronically decaying tau leptons with one associated track, and of 4% for the case of three associated tracks, inclusive in pseudorapidity and for a visible transverse energy greater than 20 GeV. For hadronic tau lepton decays selected by offline algorithms, the tau trigger identification efficiency is measured with a precision of 2-8%, depending on the transverse energy. The performance of the tau algorithms, both offline and at the trigger level, is found to be stable with respect to the number of concurrent proton-proton interactions and has supported a variety of physics results using hadronically decaying tau leptons at ATLAS.
4.
  • Aad, G., et al. (författare)
  • Measurement of the top-quark mass in the fully hadronic decay channel from ATLAS data at [Formula: see text].
  • 2015
  • Ingår i: European Physical Journal C. Particles and Fields. - Springer. - 1434-6044. ; 75:4
  • Tidskriftsartikel (refereegranskat)abstract
    • The mass of the top quark is measured in a data set corresponding to 4.6 [Formula: see text] of proton-proton collisions with centre-of-mass energy [Formula: see text] TeV collected by the ATLAS detector at the LHC. Events consistent with hadronic decays of top-antitop quark pairs with at least six jets in the final state are selected. The substantial background from multijet production is modelled with data-driven methods that utilise the number of identified [Formula: see text]-quark jets and the transverse momentum of the sixth leading jet, which have minimal correlation. The top-quark mass is obtained from template fits to the ratio of three-jet to dijet mass. The three-jet mass is calculated from the three jets produced in a top-quark decay. Using these three jets the dijet mass is obtained from the two jets produced in the [Formula: see text] boson decay. The top-quark mass obtained from this fit is thus less sensitive to the uncertainty in the energy measurement of the jets. A binned likelihood fit yields a top-quark mass of [Formula: see text].
5.
  • Aad, G., et al. (författare)
  • Performance of the ATLAS muon trigger in pp collisions at [Formula: see text] TeV.
  • 2015
  • Ingår i: European Physical Journal C. Particles and Fields. - Springer. - 1434-6044. ; 75:3
  • Tidskriftsartikel (refereegranskat)abstract
    • The performance of the ATLAS muon trigger system is evaluated with proton-proton collision data collected in 2012 at the Large Hadron Collider at a centre-of-mass energy of 8 TeV. It is primarily evaluated using events containing a pair of muons from the decay of [Formula: see text] bosons. The efficiency of the single-muon trigger is measured for muons with transverse momentum [Formula: see text] GeV, with a statistical uncertainty of less than 0.01 % and a systematic uncertainty of 0.6 %. The [Formula: see text] range for efficiency determination is extended by using muons from decays of [Formula: see text] mesons, [Formula: see text] bosons, and top quarks. The muon trigger shows highly uniform and stable performance. The performance is compared to the prediction of a detailed simulation.
6.
  • Aad, G., et al. (författare)
  • Search for anomalous production of prompt same-sign lepton pairs and pair-produced doubly charged Higgs bosons with root s=8 TeV pp collisions using the ATLAS detector
  • 2015
  • Ingår i: Journal of High Energy Physics. - Springer. - 1029-8479. ; :3
  • Tidskriftsartikel (refereegranskat)abstract
    • A low-background inclusive search for new physics in events with same-sign dileptons is presented. The search uses proton-proton collisions corresponding to 20.3 fb(-1) of integrated luminosity taken in 2012 at a centre-of-mass energy of 8TeV with the ATLAS detector at the LHC. Pairs of isolated leptons with the same electric charge and large transverse momenta of the type e(+/-) e(+/-), e(+/-) mu(+/-), and mu(+/-) mu(+/-) are selected and their invariant mass distribution is examined. No excess of events above the expected level of Standard Model background is found. The results are used to set upper limits on the cross-sections for processes beyond the Standard Model. Limits are placed as a function of the dilepton invariant mass within a fiducial region corresponding to the signal event selection criteria. Exclusion limits are also derived for a specific model of doubly charged Higgs boson production.
  •  
7.
  • Barucca, G, et al. (författare)
  • Precision resonance energy scans with the PANDA experiment at FAIR Sensitivity study for width and line shape measurements of the X(3872)
  • 2019
  • Ingår i: European Physical Journal A. - Springer. - 1434-6001. ; 55:3
  • Tidskriftsartikel (refereegranskat)abstract
    • .This paper summarises a comprehensive Monte Carlo simulation study for precision resonance energy scan measurements. Apart from the proof of principle for natural width and line shape measurements of very narrow resonances with PANDA, the achievable sensitivities are quantified for the concrete example of the charmonium-like X(3872) state discussed to be exotic, and for a larger parameter space of various assumed signal cross-sections, input widths and luminosity combinations. PANDA is the only experiment that will be able to perform precision resonance energy scans of such narrow states with quantum numbers of spin and parities that differ from JPC=1--.
8.
  • Aad, G., et al. (författare)
  • Simultaneous measurements of the t(t)over-bar, W+W-, and Z/gamma* -> tau tau production cross-sections in pp collisions at root s=7 TeV with the ATLAS detector
  • 2015
  • Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - American Physical Society. - 1550-2368. ; 91:5
  • Tidskriftsartikel (refereegranskat)abstract
    • Simultaneous measurements of the t (t) over bar, W+W-, and Z/gamma* -> tau tau production cross-sections using an integrated luminosity of 4.6 fb(-1) of pp collisions at root s = 7 TeV collected by the ATLAS detector at the LHC are presented. Events are selected with two high transverse momentum leptons consisting of an oppositely charged electron and muon pair. The three processes are separated using the distributions of the missing transverse momentum of events with zero and greater than zero jet multiplicities. Measurements of the fiducial cross-section are presented along with results that quantify for the first time the underlying correlations in the predicted and measured cross-sections due to proton parton distribution functions. These results indicate that the correlated next-to-leading-order predictions for t (t) over bar and Z/gamma* -> tau tau underestimate the data, while those at next-to-next-to-leading-order generally describe the data well. The full cross-sections are measured to be sigma(t (t) over bar) = 181.2 +/- 2.8(-9.5)(+9.7) +/- 3.3 +/- 3.3 pb, sigma(W+W-) = 53.3 +/- 2.7(-8.0)(+7.3) +/- 1.0 +/- 0.5 pb, and sigma(Z/gamma* -> tau tau) = 1174 +/- 24(-87)(+72) +/- 21 +/- 9 pb, where the cited uncertainties are due to statistics, systematic effects, luminosity and the LHC beam energy measurement, respectively. The W+W- measurement includes the small contribution from Higgs boson decays, H -> W+W-.
  •  
9.
  • Abulaiti, Yiming, et al. (författare)
  • Searches for heavy long-lived charged particles with the ATLAS detector in proton-proton collisions at root s=8 TeV
  • 2015
  • Ingår i: Journal of High Energy Physics. - Springer. - 1029-8479. ; :1
  • Tidskriftsartikel (refereegranskat)abstract
    • Searches for heavy long-lived charged particles are performed using a data sample of 19.1 fb(-1) from proton-proton collisions at a centre-of-mass energy of root s = 8 TeV collected by the ATLAS detector at the Large Hadron Collider. No excess is observed above the estimated background and limits are placed on the mass of long-lived particles in various supersymmetric models. Long-lived tau sleptons in models with gauge-mediated symmetry breaking are excluded up to masses between 440 and 385 GeV for tan,3 between 10 and 50, with a 290 GeV limit in the case where only direct tau slepton production is considered. In the context of simplified LeptoSUSY models, where sleptons are stable and have a mass of 300 GeV, squark and gluino masses are excluded up to a mass of 1500 and 1360 GeV, respectively. Directly produced charginos, in simplified models where they are nearly degenerate to the lightest neutralino, are excluded up to a mass of 620 GeV. R-hadrons, composites containing a gluino, bottom squark or top squark, are excluded up to a mass of 1270, 845 and 900 GeV, respectively, using the full detector; and up to a mass of 1260, 835 and 870 GeV using an approach disregarding information from the muon spectrometer.
10.
  • Aad, G, et al. (författare)
  • Measurement of the charge asymmetry in dileptonic decays of top quark pairs in pp collisions at root s=7 TeV using the ATLAS detector
  • 2015
  • Ingår i: Journal of High Energy Physics. - Springer. - 1029-8479. ; :5
  • Tidskriftsartikel (refereegranskat)abstract
    • A measurement of the top-antitop (t (t) over bar) charge asymmetry is presented using data corresponding to an integrated luminosity of 4.6 fb(-1) of LHC pp collisions at a centre-of-mass energy of 7 TeV collected by the ATLAS detector. Events with two charged leptons, at least two jets and large missing transverse momentum are selected. Two observables are studied: A(C)(ll) based on the identified charged leptons, and A(C)(t (t) over bar), based on the reconstructed t (t) over bar final state. The asymmetries are measured to be A(C)(ll) =0.024 +/- 0.015 (stat.) +/- 0.009 (syst.), A(C)(t (t) over bar) = 0.021 +/- 0.025 (stat.) +/- 0.017 (syst.). The measured values are in agreement with the Standard Model predictions.
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