| 1. |
- Aad, G, et al.
(författare)
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Beam-induced and cosmic-ray backgrounds observed in the ATLAS detector during the LHC 2012 proton-proton running period
- 2016
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Ingår i: Journal of Instrumentation. - : IOP PUBLISHING LTD. - 1748-0221. ; 11:5
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Tidskriftsartikel (refereegranskat)abstract
- This paper discusses various observations on beam-induced and cosmic-ray backgrounds in the ATLAS detector during the LHC 2012 proton-proton run. Building on published results based on 2011 data, the correlations between background and residual pressure of the beam vacuum are revisited. Ghost charge evolution over 2012 and its role for backgrounds are evaluated. New methods to monitor ghost charge with beam-gas rates are presented and observations of LHC abort gap population by ghost charge are discussed in detail. Fake jets from colliding bunches and from ghost charge are analysed with improved methods, showing that ghost charge in individual radio-frequency buckets of the LHC can be resolved. Some results of two short periods of dedicated cosmic-ray background data-taking are shown; in particular cosmic-ray muon induced fake jet rates are compared to Monte Carlo simulations and to the fake jet rates from beam background. A thorough analysis of a particular LHC fill, where abnormally high background was observed, is presented. Correlations between backgrounds and beam intensity losses in special fills with very high β∗ are studied. © 2016 CERN for the benefit of the ATLAS collaboration.
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| 2. |
- Aad, G, et al.
(författare)
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Measurement of the ZZ production cross section in pp collisions at √s = 13 TeV with the ATLAS detector
- 2016
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Ingår i: Physical Review Letters. - : American Physical Society. - 1079-7114 .- 0031-9007. ; 116:10
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Tidskriftsartikel (refereegranskat)abstract
- The ZZ production cross section in proton-proton collisions at 13 TeV center-of-mass energy is measured using 3.2 fb-1 of data recorded with the ATLAS detector at the Large Hadron Collider. The considered Z boson candidates decay to an electron or muon pair of mass 66-116 GeV. The cross section is measured in a fiducial phase space reflecting the detector acceptance. It is also extrapolated to a total phase space for Z bosons in the same mass range and of all decay modes, giving 16.7-2.0+2.2(stat)+0.9-0.7(syst)+1.0-0.7(lumi) pb. The results agree with standard model predictions. © 2016 CERN. Published by the American Physical Society under the terms of the "http://creativecommons.org/licenses/by/3.0/" Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.
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| 3. |
- Aad, G, et al.
(författare)
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Performance of b-jet identification in the ATLAS experiment
- 2016
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Ingår i: Journal of Instrumentation. - : Institute of Physics (IOP). - 1748-0221. ; 11:4
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Tidskriftsartikel (refereegranskat)abstract
- The identification of jets containing b hadrons is important for the physics programme of the ATLAS experiment at the Large Hadron Collider. Several algorithms to identify jets containing b hadrons are described, ranging from those based on the reconstruction of an inclusive secondary vertex or the presence of tracks with large impact parameters to combined tagging algorithms making use of multi-variate discriminants. An independent b-tagging algorithm based on the reconstruction of muons inside jets as well as the b-tagging algorithm used in the online trigger are also presented. The b-jet tagging efficiency, the c-jet tagging efficiency and the mistag rate for light flavour jets in data have been measured with a number of complementary methods. The calibration results are presented as scale factors defined as the ratio of the efficiency (or mistag rate) in data to that in simulation. In the case of b jets, where more than one calibration method exists, the results from the various analyses have been combined taking into account the statistical correlation as well as the correlation of the sources of systematic uncertainty. © CERN 2016 for the benefit of the ATLAS collaboration, published under the terms of the Creative Commons Attribution 3.0 License by IOP Publishing Ltd and Sissa Medialab srl.
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| 4. |
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| 5. |
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| 6. |
- Abolins, M., et al.
(författare)
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The ATLAS Data Acquisition and High Level Trigger system
- 2016
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Ingår i: Journal of Instrumentation. - 1748-0221 .- 1748-0221. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- This paper describes the data acquisition and high level trigger system of the ATLAS experiment at the Large Hadron Collider at CERN, as deployed during Run 1. Data flow as well as control, configuration and monitoring aspects are addressed. An overview of the functionality of the system and of its performance is presented and design choices are discussed.
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| 7. |
- Abulaiti, Yiming, et al.
(författare)
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A measurement of material in the ATLAS tracker using secondary hadronic interactions in 7 TeV p p collisions
- 2016
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Ingår i: Journal of Instrumentation. - : IOP PUBLISHING LTD. - 1748-0221 .- 1748-0221. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- Knowledge of the material in the ATLAS inner tracking detector is crucial in under-standing the reconstruction of charged-particle tracks, the performance of algorithms that identify jets containing b-hadrons and is also essential to reduce background in searches for exotic particles that can decay within the inner detector volume. Interactions of primary hadrons produced in pp collisions with the material in the inner detector are used to map the location and amount of this material. The hadronic interactions of primary particles may result in secondary vertices, which in this analysis are reconstructed by an inclusive vertex-finding algorithm. Data were collected using minimum-bias triggers by the ATLAS detector operating at the LHC during 2010 at centre-of-mass energy root s = 7 TeV, and correspond to an integrated luminosity of 19 nb(-1). Kinematic properties of these secondary vertices are used to study the validity of the modelling of hadronic interactions in simulation. Secondary-vertex yields are compared between data and simulation over a volume of about 0.7m(3) around the interaction point, and agreement is found within overall uncertainties.
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| 8. |
- Abulaiti, Yiming, et al.
(författare)
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A new method to distinguish hadronically decaying boosted Z bosons from W bosons using the ATLAS detector
- 2016
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 76:5
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Tidskriftsartikel (refereegranskat)abstract
- The distribution of particles inside hadronic jets produced in the decay of boosted W and Z bosons can be used to discriminate such jets from the continuum background. Given that a jet has been identified as likely resulting from the hadronic decay of a boosted W or Z boson, this paper presents a technique for further differentiating Z bosons from W bosons. The variables used are jet mass, jet charge, and a b-tagging discriminant. A likelihood tagger is constructed from these variables and tested in the simulation of W' -> WZ for bosons in the transverse momentum range 200 GeV < p(T) < 400 GeV in root s = 8 TeV pp collisions with the ATLAS detector at the LHC. For Z-boson tagging efficiencies of epsilon(Z) = 90, 50, and 10 %, one can achieve W+-boson tagging rejection factors (1/epsilon(W+)) of 1.7, 8.3 and 1000, respectively. It is not possible to measure these efficiencies in the data due to the lack of a pure sample of high p(T), hadronically decaying Z bosons. However, the modelling of the tagger inputs for boosted W bosons is studied in data using a t (t) over bar -enriched sample of events in 20.3 fb(-1) of data at root s = 8 TeV. The inputs are well modelled within uncertainties, which builds confidence in the expected tagger performance.
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| 9. |
- Abulaiti, Yiming, et al.
(författare)
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A search for prompt lepton-jets in pp collisions at root s=8 TeV with the ATLAS detector
- 2016
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Ingår i: Journal of High Energy Physics (JHEP). - : Springer. - 1126-6708 .- 1029-8479. ; :2
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Tidskriftsartikel (refereegranskat)abstract
- A search is presented for a new, light boson with a mass of about 1 GeV and decaying promptly to jets of collimated electrons and/or muons (lepton-jets). The analysis is performed with 20.3 fb(-1) of data collected by the ATLAS detector at the Large Hadron Collider in proton-proton collisions at a centre-of-mass energy of 8 TeV. Events are required to contain at least two lepton-jets. This study finds no statistically significant deviation from predictions of the Standard Model and places 95% confidence-level upper limits on the contribution of new phenomena beyond the SM, incuding SUSY-portal and Higgs-portal models, on the number of events with lepton-jets.
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| 10. |
- Abulaiti, Yiming, et al.
(författare)
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A search for top squarks with R-parity-violating decays to all-hadronic final states with the ATLAS detector in root s=8 TeV proton-proton collisions
- 2016
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Ingår i: Journal of High Energy Physics (JHEP). - 1126-6708 .- 1029-8479. ; :6
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Tidskriftsartikel (refereegranskat)abstract
- A search for the pair production of top squarks, each with R-parity-violating decays into two Standard Model quarks, is performed using 17.4 fb(-1) of root s = 8 TeV proton-proton collision data recorded by the ATLAS experiment at the LITC. Each top squark is assumed to decay to a b- and an 8-quark, leading to four quarks in the final state. Background discrimination is achieved with the use of b-tagging and selections on the mass and substructure of large-radius jets, providing sensitivity to top squark masses as low as 100 GeV. No evidence of an excess beyond the Standard Model background prediction is observed and top squalls decaying to bs are excluded for top squark masses in the range 100 <= m((t) over tilde) <= 315 GeV at 95% confidence level.
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