| 1. |
- Abulaiti, Yiming, et al.
(author)
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A measurement of the calorimeter response to single hadrons and determination of the jet energy scale uncertainty using LHC Run-1 pp-collision data with the ATLAS detector
- 2017
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In: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 77:1
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Journal article (peer-reviewed)abstract
- A measurement of the calorimeter response to isolated charged hadrons in the ATLAS detector at the LHC is presented. This measurement is performed with 3.2 nb(-1) of proton-proton collision data at root s = 7 TeV from 2010 and 0.1 nb(-1) of data at root s = 8 TeV from 2012. A number of aspects of the calorimeter response to isolated hadrons are explored. After accounting for energy deposited by neutral particles, there is a 5% discrepancy in the modelling, using various sets of GEANT4 hadronic physics models, of the calorimeter response to isolated charged hadrons in the central calorimeter region. The description of the response to anti-protons at low momenta is found to be improved with respect to previous analyses. The electromagnetic and hadronic calorimeters are also examined separately, and the detector simulation is found to describe the response in the hadronic calorimeter well. The jet energy scale uncertainty and correlations in scale between jets of different momenta and pseudorapidity are derived based on these studies. The uncertainty is 2-5% for jets with transverse momenta above 2 TeV, where this method provides the jet energy scale uncertainty for ATLAS.
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| 2. |
- Abulaiti, Yiming, et al.
(author)
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A search for pair-produced resonances in four-jet final states at root s=13 TeV with the ATLAS detector
- 2018
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In: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 78:3
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Journal article (peer-reviewed)abstract
- A search for massive coloured resonances which are pair-produced and decay into two jets is presented. The analysis uses 36.7 fb(-1) of root s = 13 TeV pp collision data recorded by the ATLAS experiment at the LHC in 2015 and 2016. No significant deviation from the background prediction is observed. Results are interpreted in a SUSY simplified model where the lightest supersymmetric particle is the top squark, (t) over tilde, which decays promptly into two quarks through R-parity-violating couplings. Top squarks with masses in the range 100 GeV < m((T) over tilde) < 410 GeV are excluded at 95% confidence level. If the decay is into a b-quark and a light quark, a dedicated selection requiring two b-tags is used to exclude masses in the ranges 100 GeV < m((t) over tilde) < 470 GeV and 480 GeV < m(<(t)over tilde>) < 610 GeV. Additional limits are set on the pair-production of massive colour-octet resonances.
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| 3. |
- Abulaiti, Yiming, et al.
(author)
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Charged-particle distributions at low transverse momentum in root s=13 TeV pp interactions measured with the ATLAS detector at the LHC
- 2016
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In: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 76:9
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Journal article (peer-reviewed)abstract
- Measurements of distributions of charged particles produced in proton-proton collisions with a centre-of-mass energy of 13 TeV are presented. The data were recorded by the ATLAS detector at the LHC and correspond to an integrated luminosity of 151 mu b(-1). The particles are required to have a transverse momentum greater than 100 MeV and an absolute pseudorapidity less than 2.5. The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity and the dependence of the mean transverse momentum on multiplicity are measured in events containing at least two charged particles satisfying the above kinematic criteria. The results are corrected for detector effects and compared to the predictions from several Monte Carlo event generators.
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| 4. |
- Abulaiti, Yiming, et al.
(author)
-
Charged-particle distributions in pp interactions at root s=8TeV measured with the ATLAS detector
- 2016
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In: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 76:7
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Journal article (peer-reviewed)abstract
- This paper presents measurements of distributions of charged particles which are produced in proton-proton collisions at a centre-of-mass energy of root s = 8TeV 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 mu b(-1) was used. A minimumbias 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.
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| 5. |
- Abulaiti, Yiming, et al.
(author)
-
Determination of the strong coupling constant alpha(s) from transverse energy-energy correlations in multijet events at root s=8 TeV using the ATLAS detector
- 2017
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In: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 77:12
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Journal article (peer-reviewed)abstract
- Measurements of transverse energy-energy correlations and their associated asymmetries in multi-jet events using the ATLAS detector at the LHC are presented. The data used correspond to vs = 8 TeV proton-proton collisions with an integrated luminosity of 20.2 fb(-1). The results are presented in bins of the scalar sum of the transverse momenta of the two leading jets, unfolded to the particle level and compared to the predictions from Monte Carlo simulations. A comparison with next-to-leading-order perturbative QCD is also performed, showing excellent agreement within the uncertainties. From this comparison, the value of the strong coupling constant is extracted for different energy regimes, thus testing the running of alpha(s)(mu) predicted in QCD up to scales over 1 TeV. A global fit to the transverse energy-energy correlation distributions yields alpha(s)(m(Z)) = 0.1162 +/- 0.0011 (exp.)(-0.0070)(+0.0084) (theo.), while a global fit to the asymmetry distributions yields a value of alpha(s)(m(Z)) = 0.1196 +/- 0.0013 (exp.)(-0.0045)(+0.0075) (theo.).
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| 6. |
- Abulaiti, Yiming, et al.
(author)
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Electron efficiency measurements with the ATLAS detector using 2012 LHC proton-proton collision data
- 2017
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In: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 77:3
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Journal article (peer-reviewed)abstract
- This paper describes the algorithms for the reconstruction and identification of electrons in the central region of the ATLAS detector at the Large Hadron Collider (LHC). These algorithms were used for all ATLAS results with electrons in the final state that are based on the 2012 pp collision data produced by the LHC at root s = 8 TeV. The efficiency of these algorithms, together with the charge misidentification rate, is measured in data and evaluated in simulated samples using electrons from Z -> ee, Z -> ee gamma and J/Psi -> ee decays. For these efficiency measurements, the full recorded data set, corresponding to an integrated luminosity of 20.3 fb(-1), is used. Based on a new reconstruction algorithm used in 2012, the electron reconstruction efficiency is 97% for electrons with E-T = 15 GeV and 99% at E-T = 50 GeV. Combining this with the efficiency of additional selection criteria to reject electrons from background processes or misidentified hadrons, the efficiency to reconstruct and identify electrons at the ATLAS experiment varies from 65 to 95%, depending on the transverse momentum of the electron and background rejection.
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| 7. |
- Abulaiti, Yiming, et al.
(author)
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Fiducial, total and differential cross-section measurements of t-channel single top-quark production in pp collisions at 8TeV using data collected by the ATLAS detector
- 2017
-
In: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 77:8
-
Journal article (peer-reviewed)abstract
- Detailed measurements of t-channel single top-quark production are presented. They use 20.2 fb(-1) of data collected by the ATLAS experiment in proton-proton collisions at a centre-of-mass energy of 8 TeV at the LHC. Total, fiducial and differential cross-sections are measured for both top-quark and top-antiquark production. The fiducial cross-section is measured with a precision of 5.8% (top quark) and 7.8% (top antiquark), respectively. The total cross-sections are measured to be stot(tq) = 56.7(-3.8)(+4.3) pb for top-quark production and sigma(tot)((t) over barq) = 32.9(-2.7)(+3.0) pb for top-antiquark production, in agreement with the Standard Model prediction. In addition, the ratio of top-quark to top-antiquark production cross-sections is determined to be R-t = 1.72 +/- 0.09. The differential cross-sections as a function of the transverse momentum and rapidity of both the top quark and the top antiquark are measured at both the parton and particle levels. The transverse momentum and rapidity differential cross-sections of the accompanying jet from the t-channel scattering are measured at particle level. All measurements are compared to various Monte Carlo predictions as well as to fixed-order QCD calculations where available.
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| 8. |
- Abulaiti, Yiming, et al.
(author)
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Identification and rejection of pile-up jets at high pseudorapidity with the ATLAS detector
- 2017
-
In: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 77:9
-
Journal article (peer-reviewed)abstract
- The rejection of forward jets originating from additional proton-proton interactions (pile-up) is crucial for a variety of physics analyses at the LHC, including Standard Model measurements and searches for physics beyond the Standard Model. The identification of such jets is challenging due to the lack of track and vertex information in the pseudorapidity range vertical bar eta vertical bar > 2.5. This paper presents a novel strategy for forward pile-up jet tagging that exploits jet shapes and topological jet correlations in pile-up interactions. Measurements of the per-jet tagging efficiency are presented using a data set of 3.2 fb(-1) of proton-proton collisions at a centre-of-mass energy of 13 TeV collected with the ATLAS detector. The fraction of pile-up jets rejected in the range 2.5 < vertical bar eta vertical bar < 4.5 is estimated in simulated events with an average of 22 interactions per bunch-crossing. It increases with jet transverse momentum and, for jets with transverse momentum between 20 and 50 GeV, it ranges between 49% and 67% with an efficiency of 85% for selecting hard-scatter jets. A case study is performed in Higgs boson production via the vector-boson fusion process, showing that these techniques mitigate the background growth due to additional proton-proton interactions, thus enhancing the reach for such signatures.
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| 9. |
- Abulaiti, Yiming, et al.
(author)
-
Jet reconstruction and performance using particle flow with the ATLAS Detector
- 2017
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In: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052 .- 0143-0807 .- 1361-6404. ; 77:7
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Journal article (peer-reviewed)abstract
- This paper describes the implementation and performance of a particle flow algorithm applied to 20.2 fb(-1) of ATLAS data from 8 TeV proton-proton collisions in Run 1 of the LHC. The algorithm removes calorimeter energy deposits due to charged hadrons from consideration during jet reconstruction, instead using measurements of their momenta from the inner tracker. This improves the accuracy of the charged-hadron measurement, while retaining the calorimeter measurements of neutral-particle energies. The paper places emphasis on how this is achieved, while minimising double-counting of charged-hadron signals between the inner tracker and calorimeter. The performance of particle flow jets, formed from the ensemble of signals from the calorimeter and the inner tracker, is compared to that of jets reconstructed from calorimeter energy deposits alone, demonstrating improvements in resolution and pile-up stability.
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| 10. |
- Abulaiti, Yiming, et al.
(author)
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Luminosity determination in pp collisions at root s=8 TeV using the ATLAS detector at the LHC
- 2016
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In: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 76:12
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Journal article (peer-reviewed)abstract
- The luminosity determination for the ATLAS detector at the LHC during pp collisions at root s = 8 TeV in 2012 is presented. The evaluation of the luminosity scale is performed using several luminometers, and comparisons between these luminosity detectors are made to assess the accuracy, consistency and long-term stability of the results. A luminosity uncertainty of delta L/L = +/- 1.9% is obtained for the 22.7 fb(-1) of pp collision data delivered to ATLAS at root s = 8 TeV in 2012.
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