| 1. |
- Assamagan, Kétévi A., et al.
(författare)
-
The ATLAS discovery potential for a heavy charged Higgs boson in gg→tbH± with H±→tb
- 2005
-
Ingår i: The European Physical Journal C: Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 39:2, s. 25-40
-
Tidskriftsartikel (refereegranskat)abstract
- The feasibility of detecting a heavy charged Higgs boson, mH±>mt+mb, decaying in the H±→tb channel is studied with the fast simulation of the ATLAS detector. We study the gg→H±tb production process at the LHC which together with the aforementioned decay channel leads to four b–quarks in the final state. The whole production and decay chain reads gg→tbH±→ ttbb→bbbblνqq' . Combinatorial background is a major difficulty in this multi–jet environment but can be overcome by employing multivariate techniques in the event reconstruction. Requiring four b–tagged jets in the event helps to effectively suppress the Standard Model backgrounds but leads to no significant improvement in the discovery potential compared to analyses requiring only three b–tagged jets. This study indicates that charged Higgs bosons can be discovered at the LHC up to high masses (mH±>400 GeV) in the case of large tanβ.
|
|
| 2. |
- Aaboud, M, et al.
(författare)
-
Charged-particle distributions at low transverse momentum in √s=13 TeV pp interactions measured with the ATLAS detector at the LHC
- 2016
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 76:9
-
Tidskriftsartikel (refereegranskat)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 μ 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. © 2016, CERN for the benefit of the ATLAS collaboration.
|
|
| 3. |
- Aaboud, M, et al.
(författare)
-
Determination of the strong coupling constant αs from transverse energy–energy correlations in multijet events at √s=8TeV using the ATLAS detector
- 2017
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 77:12
-
Tidskriftsartikel (refereegranskat)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 s=8TeV proton–proton collisions with an integrated luminosity of 20.2fb-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 αs(μ) predicted in QCD up to scales over 1TeV. A global fit to the transverse energy–energy correlation distributions yields αs(mZ)=0.1162±0.0011(exp.)-0.0070+0.0084(theo.), while a global fit to the asymmetry distributions yields a value of αs(mZ)=0.1196±0.0013(exp.)-0.0045+0.0075(theo.). © 2017, CERN for the benefit of the ATLAS collaboration.
|
|
| 4. |
- Aaboud, M., et al.
(författare)
-
Direct top-quark decay width measurement in the t(t)over-bar lepton plus jets channel at root s=8 TeV with the ATLAS experiment
- 2018
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 78
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents a direct measurement of the decay width of the top quark using t (t) over bar events in the lepton+jets final state. The data sample was collected by the ATLAS detector at the LHC in proton-proton collisions at a centre-of-mass energy of 8 TeV and corresponds to an integrated luminosity of 20.2 fb(-1). The decay width of the top quark is measured using a template fit to distributions of kinematic observables associated with the hadronically and semileptonically decaying top quarks. The result, Gamma(t) = 1.76 +/- 0.33 (stat.) (+0.79)(-0.68) (syst.) GeV for a top-quark mass of 172.5 GeV, is consistent with the prediction of the Standard Model.
|
|
| 5. |
- Aaboud, M, et al.
(författare)
-
Direct top-quark decay width measurement in the tt¯ lepton+jets channel at √s=8TeV with the ATLAS experiment
- 2018
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 78:2
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents a direct measurement of the decay width of the top quark using tt¯ events in the lepton+jets final state. The data sample was collected by the ATLAS detector at the LHC in proton–proton collisions at a centre-of-mass energy of 8 TeV and corresponds to an integrated luminosity of 20.2 fb- 1. The decay width of the top quark is measured using a template fit to distributions of kinematic observables associated with the hadronically and semileptonically decaying top quarks. The result, Γt=1.76±0.33(stat.)-0.68+0.79(syst.)GeV for a top-quark mass of 172.5 GeV, is consistent with the prediction of the Standard Model. © 2018, CERN for the benefit of the ATLAS collaboration.
|
|
| 6. |
|
|
| 7. |
|
|
| 8. |
- Aaboud, M, et al.
(författare)
-
Measurement of colour flow using jet-pull observables in tt¯ events with the ATLAS experiment at √s=13TeV
- 2018
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 78:10
-
Tidskriftsartikel (refereegranskat)abstract
- Previous studies have shown that weighted angular moments derived from jet constituents encode the colour connections between partons that seed the jets. This paper presents measurements of two such distributions, the jet-pull angle and jet-pull magnitude, both of which are derived from the jet-pull angular moment. The measurement is performed in tt¯ events with one leptonically decaying W boson and one hadronically decaying W boson, using 36.1fb-1 of pp collision data recorded by the ATLAS detector at s=13TeV delivered by the Large Hadron Collider. The observables are measured for two dijet systems, corresponding to the colour-connected daughters of the W boson and the two b-jets from the top-quark decays, which are not expected to be colour connected. To allow the comparison of the measured distributions to colour model predictions, the measured distributions are unfolded to particle level, after correcting for experimental effects introduced by the detector. While good agreement can be found for some combinations of predictions and observables, none of the predictions describes the data well across all observables. © 2018, CERN for the benefit of the ATLAS collaboration.
|
|
| 9. |
- Aaboud, M, et al.
(författare)
-
Measurement of fiducial and differential W+W- production cross-sections at √s=13 TeV with the ATLAS detector
- 2019
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 79:10
-
Tidskriftsartikel (refereegranskat)abstract
- A measurement of fiducial and differential cross-sections for W+W- production in proton–proton collisions at s=13 TeV with the ATLAS experiment at the Large Hadron Collider using data corresponding to an integrated luminosity of 36.1 fb - 1 is presented. Events with one electron and one muon are selected, corresponding to the decay of the diboson system as WW→ e±νμ∓ν. To suppress top-quark background, events containing jets with a transverse momentum exceeding 35 GeV are not included in the measurement phase space. The fiducial cross-section, six differential distributions and the cross-section as a function of the jet-veto transverse momentum threshold are measured and compared with several theoretical predictions. Constraints on anomalous electroweak gauge boson self-interactions are also presented in the framework of a dimension-six effective field theory. © 2019, CERN for the benefit of the ATLAS collaboration.
|
|
| 10. |
- Aaboud, M, et al.
(författare)
-
Measurement of lepton differential distributions and the top quark mass in tt¯ production in pp collisions at √s=8 TeV with the ATLAS detector
- 2017
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 77:11
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents single lepton and dilepton kinematic distributions measured in dileptonic tt¯ events produced in 20.2fb - 1 of s=8 TeV pp collisions recorded by the ATLAS experiment at the LHC. Both absolute and normalised differential cross-sections are measured, using events with an opposite-charge eμ pair and one or two b-tagged jets. The cross-sections are measured in a fiducial region corresponding to the detector acceptance for leptons, and are compared to the predictions from a variety of Monte Carlo event generators, as well as fixed-order QCD calculations, exploring the sensitivity of the cross-sections to the gluon parton distribution function. Some of the distributions are also sensitive to the top quark pole mass; a combined fit of NLO fixed-order predictions to all the measured distributions yields a top quark mass value of mtpole=173.2±0.9±0.8±1.2 GeV, where the three uncertainties arise from data statistics, experimental systematics, and theoretical sources. © 2017, CERN for the benefit of the ATLAS collaboration.
|
|
| 11. |
- Aaboud, M, et al.
(författare)
-
Measurement of longitudinal flow decorrelations in Pb+Pb collisions at √sNN=2.76 and 5.02 TeV with the ATLAS detector
- 2018
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 78:2
-
Tidskriftsartikel (refereegranskat)abstract
- Measurements of longitudinal flow correlations are presented for charged particles in the pseudorapidity range | η| < 2.4 using 7 and 470 μ b - 1 of Pb+Pb collisions at sNN=2.76 and 5.02 TeV, respectively, recorded by the ATLAS detector at the LHC. It is found that the correlation between the harmonic flow coefficients vn measured in two separated η intervals does not factorise into the product of single-particle coefficients, and this breaking of factorisation, or flow decorrelation, increases linearly with the η separation between the intervals. The flow decorrelation is stronger at 2.76 TeV than at 5.02 TeV. Higher-order moments of the correlations are also measured, and the corresponding linear coefficients for the kth -moment of the vn are found to be proportional to k for v3, but not for v2. The decorrelation effect is separated into contributions from the magnitude of vn and the event-plane orientation, each as a function of η. These two contributions are found to be comparable. The longitudinal flow correlations are also measured between vn of different order in n. The decorrelations of v2 and v3 are found to be independent of each other, while the decorrelations of v4 and v5 are found to be driven by the nonlinear contribution from v22 and v2v3, respectively. © 2018, CERN for the benefit of the ATLAS collaboration.
|
|
| 12. |
- Aaboud, M, et al.
(författare)
-
Measurement of the azimuthal anisotropy of charged particles produced in √sNN = 5.02 TeV Pb+Pb collisions with the ATLAS detector
- 2018
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 78:12
-
Tidskriftsartikel (refereegranskat)abstract
- Measurements of the azimuthal anisotropy in lead–lead collisions at sNN = 5.02 TeV are presented using a data sample corresponding to 0.49 nb - 1 integrated luminosity collected by the ATLAS experiment at the LHC in 2015. The recorded minimum-bias sample is enhanced by triggers for “ultra-central” collisions, providing an opportunity to perform detailed study of flow harmonics in the regime where the initial state is dominated by fluctuations. The anisotropy of the charged-particle azimuthal angle distributions is characterized by the Fourier coefficients, v2–v7, which are measured using the two-particle correlation, scalar-product and event-plane methods. The goal of the paper is to provide measurements of the differential as well as integrated flow harmonics vn over wide ranges of the transverse momentum, 0.5 < pT< 60 GeV, the pseudorapidity, | η| < 2.5, and the collision centrality 0–80%. Results from different methods are compared and discussed in the context of previous and recent measurements in Pb+Pb collisions at sNN = 2.76 TeV and 5.02 TeV. In particular, the shape of the pTdependence of elliptic or triangular flow harmonics is observed to be very similar at different centralities after scaling the vn and pTvalues by constant factors over the centrality interval 0–60% and the pTrange 0.5 < pT< 5 GeV. © 2018, CERN for the benefit of the ATLAS collaboration.
|
|
| 13. |
|
|
| 14. |
- Aaboud, M, et al.
(författare)
-
Measurement of the inclusive and fiducial tt¯ production cross-sections in the lepton+jets channel in pp collisions at √s=8TeV with the ATLAS detector
- 2018
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 78:6
-
Tidskriftsartikel (refereegranskat)abstract
- The inclusive and fiducial tt¯ production cross-sections are measured in the lepton+jets channel using 20.2fb-1 of proton–proton collision data at a centre-of-mass energy of 8 TeV recorded with the ATLAS detector at the LHC. Major systematic uncertainties due to the modelling of the jet energy scale and b-tagging efficiency are constrained by separating selected events into three disjoint regions. In order to reduce systematic uncertainties in the most important background, the W+\,jets process is modelled using Z+ jets events in a data-driven approach. The inclusive tt¯ cross-section is measured with a precision of 5.7% to be σinc(tt¯)=248.3±0.7(stat.)±13.4(syst.)±4.7(lumi.)pb, assuming a top-quark mass of 172.5 GeV. The result is in agreement with the Standard Model prediction. The cross-section is also measured in a phase space close to that of the selected data. The fiducial cross-section is σfid(tt¯)=48.8±0.1(stat.)±2.0(syst.)±0.9(lumi.)pb with a precision of 4.5%. © 2018, CERN for the benefit of the ATLAS collaboration.
|
|
| 15. |
- Aaboud, M, et al.
(författare)
-
Measurement of the top quark mass in the tt¯ → lepton+jets channel from √s=8 TeV ATLAS data and combination with previous results
- 2019
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 79:4
-
Tidskriftsartikel (refereegranskat)abstract
- The top quark mass is measured using a template method in the tt¯ → lepton + jets channel (lepton is e or μ) using ATLAS data recorded in 2012 at the LHC. The data were taken at a proton–proton centre-of-mass energy of s=8 TeV and correspond to an integrated luminosity of 20.2 fb - 1 . The tt¯ → lepton + jets channel is characterized by the presence of a charged lepton, a neutrino and four jets, two of which originate from bottom quarks (b). Exploiting a three-dimensional template technique, the top quark mass is determined together with a global jet energy scale factor and a relative b-to-light-jet energy scale factor. The mass of the top quark is measured to be mtop=172.08±0.39(stat)±0.82(syst) GeV. A combination with previous ATLAS m top measurements gives mtop=172.69±0.25(stat)±0.41(syst) GeV. © 2019, CERN for the benefit of the ATLAS collaboration.
|
|
| 16. |
- Aaboud, M, et al.
(författare)
-
Measurement of the W boson polarisation in tt¯ events from pp collisions at √s = 8 TeV in the lepton + jets channel with ATLAS
- 2017
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 77:4
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents a measurement of the polarisation of W bosons from tt¯ decays, reconstructed in events with one high-pT lepton and at least four jets. Data from pp collisions at the LHC were collected at s = 8 TeV and correspond to an integrated luminosity of 20.2 fb- 1. The angle θ∗ between the b-quark from the top quark decay and a direct W boson decay product in the W boson rest frame is sensitive to the W boson polarisation. Two different W decay products are used as polarisation analysers: the charged lepton and the down-type quark for the leptonically and hadronically decaying W boson, respectively. The most precise measurement of the W boson polarisation via the distribution of cos θ∗ is obtained using the leptonic analyser and events in which at least two of the jets are tagged as b-quark jets. The fitted fractions of longitudinal, left- and right-handed polarisation states are F0=0.709±0.019, FL=0.299±0.015 and FR=-0.008±0.014, and are the most precisely measured W boson polarisation fractions to date. Limits on anomalous couplings of the Wtb vertex are set. © 2017, CERN for the benefit of the ATLAS collaboration.
|
|
| 17. |
- Aaboud, M, et al.
(författare)
-
Measurement of τ polarisation in Z/ γ∗→ ττ decays in proton–proton collisions at √s=8 TeV with the ATLAS detector
- 2018
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 78:2
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents a measurement of the polarisation of τ leptons produced in Z/ γ∗→ ττ decays which is performed with a dataset of proton—proton collisions at s=8 TeV, corresponding to an integrated luminosity of 20.2 fb- 1 recorded with the ATLAS detector at the LHC in 2012. The Z/ γ∗→ ττ decays are reconstructed from a hadronically decaying τ lepton with a single charged particle in the final state, accompanied by a τ lepton that decays leptonically. The τ polarisation is inferred from the relative fraction of energy carried by charged and neutral hadrons in the hadronic τ decays. The polarisation is measured in a fiducial region that corresponds to the kinematic region accessible to this analysis. The τ polarisation extracted over the full phase space within the Z/ γ∗ mass range of 66
|
|
| 18. |
- Aaboud, M, et al.
(författare)
-
Measurements of inclusive and differential fiducial cross-sections of tt¯ γ production in leptonic final states at √s=13TeV in ATLAS
- 2019
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 79:5
-
Tidskriftsartikel (refereegranskat)abstract
- Inclusive and differential cross-sections for the production of a top-quark pair in association with a photon are measured with proton-proton collision data corresponding to an integrated luminosity of 36.1 fb-1, collected by the ATLAS detector at the LHC in 2015 and 2016 at a centre-of-mass energy of 13 TeV. The measurements are performed in single-lepton and dilepton final states in a fiducial volume. Events with exactly one photon, one or two leptons, a channel-dependent minimum number of jets, and at least one b-jet are selected. Neural network algorithms are used to separate the signal from the backgrounds. The fiducial cross-sections are measured to be 521±9(stat.)±41(sys.)fb and 69±3(stat.)±4(sys.)fb for the single-lepton and dilepton channels, respectively. The differential cross-sections are measured as a function of photon transverse momentum, photon absolute pseudorapidity, and angular distance between the photon and its closest lepton in both channels, as well as azimuthal opening angle and absolute pseudorapidity difference between the two leptons in the dilepton channel. All measurements are in agreement with the theoretical predictions. © 2019, CERN for the benefit of the ATLAS collaboration.
|
|
| 19. |
|
|
| 20. |
|
|
| 21. |
- Aaboud, M., et al.
(författare)
-
Search for a scalar partner of the top quark in the all-hadronic t(t)over-bar plus missing transverse momentum final state at root s=13 TeV with the ATLAS detector
- 2020
-
Ingår i: European Physical Journal C. - : Springer Nature. - 1434-6044 .- 1434-6052. ; 80:8
-
Tidskriftsartikel (refereegranskat)abstract
- A search for direct pair production of scalar partners of the top quark (top squarks or scalar third-generation up-type leptoquarks) in the all-hadronic t (t) over bar plus missing transverse momentum final state is presented. The analysis of 139 fb(-1) of root s = 13 TeV proton-proton collision data collected using the ATLAS detector at the LHC yields no significant excess over the Standard Model background expectation. To interpret the results, a supersymmetric model is used where the top squark decays via (t) over tilde -> t(*) (chi) over tilde (0)(1), with t(*) denoting an on-shell (off-shell) top quark and (chi) over tilde (0)(1) the lightest neutralino. Three specific event selections are optimised for the following scenarios. In the scenario where m((t) over tilde) > m(t) + m((chi) over tilde 10), top squark masses are excluded in the range 400-1250 GeV for (chi) over tilde (0)(1) masses below 200 GeV at 95% confidence level. In the situation where m((t) over tilde) similar to m(t) + m((chi) over tilde 10), top squarkmasses in the range 300-630 GeV are excluded, while in the case where m((t) over tilde) < m(W) + m(b) + m(<(chi)over tilde>10) (with m((t) over tilde) - m((chi) over tilde 10) >= 5 GeV), considered for the first time in an ATLAS all-hadronic search, top squark masses in the range 300-660 GeV are excluded. Limits are also set for scalar third-generation up-type leptoquarks, excluding leptoquarks with masses below 1240 GeV when considering only leptoquark decays into a top quark and a neutrino.
|
|
| 22. |
- Aaboud, M, et al.
(författare)
-
Search for new phenomena in different-flavour high-mass dilepton final states in pp collisions at √s=13 Tev with the ATLAS detector
- 2016
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 76:10
-
Tidskriftsartikel (refereegranskat)abstract
- A search is performed for a heavy particle decaying into different flavour dilepton pairs (eμ, eτ or μτ), using 3.2 fb- 1of proton–proton collision data at s=13 TeV collected in 2015 by the ATLAS detector at the Large Hadron Collider. No excess over the Standard Model prediction is observed. Limits at the 95 % credibility level are set on the mass of a Z′boson with lepton-flavour-violating couplings at 3.0, 2.7 and 2.6 TeV, and on the mass of a supersymmetric τ sneutrino with R-parity-violating couplings at 2.3, 2.2 and 1.9 TeV, for eμ, eτ and μτ final states, respectively. The results are also interpreted as limits on the threshold mass for quantum black hole production. © 2016, CERN for the benefit of the ATLAS collaboration.
|
|
| 23. |
|
|
| 24. |
- Aaboud, M, et al.
(författare)
-
Study of WWγ and WZγ production in pp collisions at √s=8TeV and search for anomalous quartic gauge couplings with the ATLAS experiment
- 2017
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 77:9
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents a study of WWγ and WZγ triboson production using events from proton–proton collisions at a centre-of-mass energy of s=8TeV recorded with the ATLAS detector at the LHC and corresponding to an integrated luminosity of 20.2 fb- 1. The WWγ production cross-section is determined using a final state containing an electron, a muon, a photon, and neutrinos (e). Upper limits on the production cross-section of the e final state and the WWγ and WZγ final states containing an electron or a muon, two jets, a photon, and a neutrino (eνjjγ or μνjjγ) are also derived. The results are compared to the cross-sections predicted by the Standard Model at next-to-leading order in the strong-coupling constant. In addition, upper limits on the production cross-sections are derived in a fiducial region optimised for a search for new physics beyond the Standard Model. The results are interpreted in the context of anomalous quartic gauge couplings using an effective field theory. Confidence intervals at 95% confidence level are derived for the 14 coupling coefficients to which WWγ and WZγ production are sensitive. © 2017, CERN for the benefit of the ATLAS collaboration.
|
|
| 25. |
- Aad, G., et al.
(författare)
-
A precise measurement of the Z-boson double-differential transverse momentum and rapidity distributions in the full phase space of the decay leptons with the ATLAS experiment at s=8 TeV
- 2024
-
Ingår i: European Physical Journal C. - : Springer Nature. - 1434-6044 .- 1434-6052. ; 84:3
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents for the first time a precise measurement of the production properties of the Z boson in the full phase space of the decay leptons. This is in contrast to the many previous precise unfolded measurements performed in the fiducial phase space of the decay leptons. The measurement is obtained from proton–proton collision data collected by the ATLAS experiment in 2012 at s=8 TeV at the LHC and corresponding to an integrated luminosity of 20.2 fb-1. The results, based on a total of 15.3 million Z-boson decays to electron and muon pairs, extend and improve a previous measurement of the full set of angular coefficients describing Z-boson decay. The double-differential cross-section distributions in Z-boson transverse momentum pT and rapidity y are measured in the pole region, defined as 80
|
|
| 26. |
|
|
| 27. |
- Aad, G, et al.
(författare)
-
Alignment of the ATLAS Inner Detector in Run 2
- 2020
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 80:12
-
Tidskriftsartikel (refereegranskat)abstract
- The performance of the ATLAS Inner Detector alignment has been studied using pp collision data at s=13TeV collected by the ATLAS experiment during Run 2 (2015–2018) of the Large Hadron Collider (LHC). The goal of the detector alignment is to determine the detector geometry as accurately as possible and correct for time-dependent movements. The Inner Detector alignment is based on the minimization of track-hit residuals in a sequence of hierarchical levels, from global mechanical assembly structures to local sensors. Subsequent levels have increasing numbers of degrees of freedom; in total there are almost 750,000. The alignment determines detector geometry on both short and long timescales, where short timescales describe movements within an LHC fill. The performance and possible track parameter biases originating from systematic detector deformations are evaluated. Momentum biases are studied using resonances decaying to muons or to electrons. The residual sagitta bias and momentum scale bias after alignment are reduced to less than ∼0.1TeV-1 and 0.9 × 10 - 3, respectively. Impact parameter biases are also evaluated using tracks within jets. © 2020, The Author(s).
|
|
| 28. |
- Aad, G., et al.
(författare)
-
ATLAS b-jet identification performance and efficiency measurement with tt¯ events in pp collisions at √s=13 TeV
- 2019
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 79:11
-
Tidskriftsartikel (refereegranskat)abstract
- The algorithms used by the ATLAS Collaboration during Run 2 of the Large Hadron Collider to identify jets containing b-hadrons are presented. The performance of the algorithms is evaluated in the simulation and the efficiency with which these algorithms identify jets containing b-hadrons is measured in collision data. The measurement uses a likelihood-based method in a sample highly enriched in tt¯ events. The topology of the t→ Wb decays is exploited to simultaneously measure both the jet flavour composition of the sample and the efficiency in a transverse momentum range from 20 to 600 GeV. The efficiency measurement is subsequently compared with that predicted by the simulation. The data used in this measurement, corresponding to a total integrated luminosity of 80.5 fb - 1, were collected in proton–proton collisions during the years 2015–2017 at a centre-of-mass energy s= 13 TeV. By simultaneously extracting both the efficiency and jet flavour composition, this measurement significantly improves the precision compared to previous results, with uncertainties ranging from 1 to 8% depending on the jet transverse momentum.
|
|
| 29. |
- Aad, G., et al.
(författare)
-
ATLAS flavour-tagging algorithms for the LHC Run 2 pp collision dataset
- 2023
-
Ingår i: European Physical Journal C. - : Institute for Ionics. - 1434-6044 .- 1434-6052. ; 83:7
-
Tidskriftsartikel (refereegranskat)abstract
- The flavour-tagging algorithms developed by the ATLAS Collaboration and used to analyse its dataset of √s=13 TeV pp collisions from Run 2 of the Large Hadron Collider are presented. These new tagging algorithms are based on recurrent and deep neural networks, and their performance is evaluated in simulated collision events. These developments yield considerable improvements over previous jet-flavour identification strategies. At the 77% b-jet identification efficiency operating point, light-jet (charm-jet) rejection factors of 170 (5) are achieved in a sample of simulated Standard Model events; similarly, at a c-jet identification efficiency of 30%, a light-jet (b-jet) rejection factor of 70 (9) is obtained.
|
|
| 30. |
|
|
| 31. |
- Aad, G., et al.
(författare)
-
Calibration of the light-flavour jet mistagging efficiency of the b-tagging algorithms with Z+jets events using 139 fb−1 of ATLAS proton–proton collision data at √s=13 TeV
- 2023
-
Ingår i: European Physical Journal C. - : Institute for Ionics. - 1434-6044 .- 1434-6052. ; 83:8
-
Tidskriftsartikel (refereegranskat)abstract
- The identification of b-jets, referred to as b-tagging, is an important part of many physics analyses in the ATLAS experiment at the Large Hadron Collider and an accurate calibration of its performance is essential for high-quality physics results. This publication describes the calibration of the light-flavour jet mistagging efficiency in a data sample of proton–proton collision events at √s=13 TeV corresponding to an integrated luminosity of 139 fb−1. The calibration is performed in a sample of Z bosons produced in association with jets. Due to the low mistagging efficiency for light-flavour jets, a method which uses modified versions of the b-tagging algorithms referred to as flip taggers is used in this work. A fit to the jet-flavour-sensitive secondary-vertex mass is performed to extract a scale factor from data, to correct the light-flavour jet mistagging efficiency in Monte Carlo simulations, while simultaneously correcting the b-jet efficiency. With this procedure, uncertainties coming from the modeling of jets from heavy-flavour hadrons are considerably lower than in previous calibrations of the mistagging scale factors, where they were dominant. The scale factors obtained in this calibration are consistent with unity within uncertainties.
|
|
| 32. |
- Aad, G, et al.
(författare)
-
Charged-particle distributions in pp interactions at √s = 8 TeV measured with the ATLAS detector
- 2016
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 76:7
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents measurements of distributions of charged particles which are produced in proton-proton collisions at a centre-of-mass energy of √s = 8 TeV 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 µb-1 was used. A minimum-bias 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 chargedparticle 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. © 2016 CERN for the benefit of the ATLAS Collaboration.
|
|
| 33. |
- Aad, G., et al.
(författare)
-
Commissioning of the ATLAS Muon Spectrometer with cosmic rays
- 2010
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 70:3, s. 875-916
-
Tidskriftsartikel (refereegranskat)abstract
- The ATLAS detector at the Large Hadron Collider has collected several hundred million cosmic ray events during 2008 and 2009. These data were used to commission the Muon Spectrometer and to study the performance of the trigger and tracking chambers, their alignment, the detector control system, the data acquisition and the analysis programs. We present the performance in the relevant parameters that determine the quality of the muon measurement. We discuss the single element efficiency, resolution and noise rates, the calibration method of the detector response and of the alignment system, the track reconstruction efficiency and the momentum measurement. The results show that the detector is close to the design performance and that the Muon Spectrometer is ready to detect muons produced in high energy proton-proton collisions.
|
|
| 34. |
- Aad, G., et al.
(författare)
-
Constraints on Higgs boson properties using WW*(-> e nu mu nu)jj production in 36.1 fb(-1) of root s=13 TeV pp collisions with the ATLAS detector
- 2022
-
Ingår i: European Physical Journal C. - : Springer. - 1434-6044 .- 1434-6052. ; 82:7
-
Tidskriftsartikel (refereegranskat)abstract
- This article presents the results of two studies of Higgs boson properties using the WW*(-> e nu mu nu)jj final state, based on a dataset corresponding to 36.1fb(-1) of root s = 13 TeV proton-proton collisions recorded by the ATLAS experiment at the Large Hadron Collider. The first study targets Higgs boson production via gluon-gluon fusion and constrains the CP properties of the effective Higgs-gluon interaction. Using angular distributions and the overall rate, a value of tan (alpha) = 0.0 +/- 0.4(stat.) +/- 0.3(syst.) is obtained for the tangent of the mixing angle for CP-even and CP-odd contributions. The second study exploits the vector-boson fusion production mechanism to probe the Higgs boson couplings to longitudinally and transversely polarised W and Z bosons in both the production and the decay of the Higgs boson; these couplings have not been directly constrained previously. The polarisation-dependent coupling-strength scale factors are defined as the ratios of the measured polarisation-dependent coupling strengths to those predicted by the Standard Model, and are determined using rate and kinematic information to be a(L) = 0.91(-0.18)(+0.10)(stat.)(-0.17)(+0.09)(syst.) and a(T) = 1.2 +/- 0.4(stat.)(-0.3)(+0.2)(syst.). These coupling strengths are translated into pseudo-observables, resulting in kappa(VV) = 0.91(-0.18)(+0.10)(stat.)(-0.17)(+0.09)(syst.) and epsilon(VV) = 0.13(-0.20)(+0.28)(stat.)(-0.10)(+0.08)(syst.). All results are consistent with the Standard Model predictions.
|
|
| 35. |
|
|
| 36. |
- Aad, G, et al.
(författare)
-
Determination of spin and parity of the Higgs boson in the [Formula: see text] decay channel with the ATLAS detector.
- 2015
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 75:5
-
Tidskriftsartikel (refereegranskat)abstract
- Studies of the spin and parity quantum numbers of the Higgs boson in the [Formula: see text] final state are presented, based on proton-proton collision data collected by the ATLAS detector at the Large Hadron Collider, corresponding to an integrated luminosity of 20.3 fb[Formula: see text] at a centre-of-mass energy of [Formula: see text] TeV. The Standard Model spin-parity [Formula: see text] hypothesis is compared with alternative hypotheses for both spin and CP. The case where the observed resonance is a mixture of the Standard-Model-like Higgs boson and CP-even ([Formula: see text]) or CP-odd ([Formula: see text]) Higgs boson in scenarios beyond the Standard Model is also studied. The data are found to be consistent with the Standard Model prediction and limits are placed on alternative spin and CP hypotheses, including CP mixing in different scenarios.
|
|
| 37. |
- Aad, G, et al.
(författare)
-
Differential cross-section measurements for the electroweak production of dijets in association with a Z boson in proton–proton collisions at ATLAS
- 2021
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 81:2
-
Tidskriftsartikel (refereegranskat)abstract
- Differential cross-section measurements are presented for the electroweak production of two jets in association with a Z boson. These measurements are sensitive to the vector-boson fusion production mechanism and provide a fundamental test of the gauge structure of the Standard Model. The analysis is performed using proton–proton collision data collected by ATLAS at s=13TeV and with an integrated luminosity of 139fb-1. The differential cross-sections are measured in the Z→ ℓ+ℓ- decay channel (ℓ= e, μ) as a function of four observables: the dijet invariant mass, the rapidity interval spanned by the two jets, the signed azimuthal angle between the two jets, and the transverse momentum of the dilepton pair. The data are corrected for the effects of detector inefficiency and resolution and are sufficiently precise to distinguish between different state-of-the-art theoretical predictions calculated using Powheg+Pythia8, Herwig7+Vbfnlo and Sherpa 2.2. The differential cross-sections are used to search for anomalous weak-boson self-interactions using a dimension-six effective field theory. The measurement of the signed azimuthal angle between the two jets is found to be particularly sensitive to the interference between the Standard Model and dimension-six scattering amplitudes and provides a direct test of charge-conjugation and parity invariance in the weak-boson self-interactions. © 2020, The Author(s).
|
|
| 38. |
|
|
| 39. |
|
|
| 40. |
- Aad, G, et al.
(författare)
-
Evidence for tt¯ tt¯ production in the multilepton final state in proton–proton collisions at √s=13 TeV with the ATLAS detector
- 2020
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 80:11
-
Tidskriftsartikel (refereegranskat)abstract
- A search is presented for four-top-quark production using an integrated luminosity of 139 fb- 1 of proton–proton collision data at a centre-of-mass energy of 13TeV collected by the ATLAS detector at the LHC. Events are selected if they contain a same-sign lepton pair or at least three leptons (electrons or muons). Jet multiplicity, jet flavour and event kinematics are used to separate signal from the background through a multivariate discriminant, and dedicated control regions are used to constrain the dominant backgrounds. The four-top-quark production cross section is measured to be 24-6+7 fb. This corresponds to an observed (expected) significance with respect to the background-only hypothesis of 4.3 (2.4) standard deviations and provides evidence for this process. © 2020, CERN for the benefit of the ATLAS collaboration.
|
|
| 41. |
- Aad, G., et al.
(författare)
-
Higgs boson production cross-section measurements and their EFT interpretation in the 4ℓ decay channel at s√=13 TeV with the ATLAS detector
- 2020
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6052 .- 1434-6044. ; 80:10
-
Tidskriftsartikel (refereegranskat)abstract
- Higgs boson properties are studied in the four-lepton decay channel (where lepton = e, μ) using 139 fb−1 of proton–proton collision data recorded at s√=13 TeV by the ATLAS experiment at the Large Hadron Collider. The inclusive cross-section times branching ratio for H→ZZ∗ decay is measured to be 1.34±0.12 pb for a Higgs boson with absolute rapidity below 2.5, in good agreement with the Standard Model prediction of 1.33±0.08 pb. Cross-sections times branching ratio are measured for the main Higgs boson production modes in several exclusive phase-space regions. The measurements are interpreted in terms of coupling modifiers and of the tensor structure of Higgs boson interactions using an effective field theory approach. Exclusion limits are set on the CP-even and CP-odd ‘beyond the Standard Model’ couplings of the Higgs boson to vector bosons, gluons and top quarks.
|
|
| 42. |
|
|
| 43. |
- 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 Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 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.
|
|
| 44. |
- Aad, G, et al.
(författare)
-
Identification of boosted Higgs bosons decaying into b-quark pairs with the ATLAS detector at 13 TeV
- 2019
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 79:10
-
Tidskriftsartikel (refereegranskat)abstract
- This paper describes a study of techniques for identifying Higgs bosons at high transverse momenta decaying into bottom-quark pairs, H→ bb¯ , for proton–proton collision data collected by the ATLAS detector at the Large Hadron Collider at a centre-of-mass energy s=13 TeV. These decays are reconstructed from calorimeter jets found with the anti-ktR= 1.0 jet algorithm. To tag Higgs bosons, a combination of requirements is used: b-tagging of R= 0.2 track-jets matched to the large-R calorimeter jet, and requirements on the jet mass and other jet substructure variables. The Higgs boson tagging efficiency and corresponding multijet and hadronic top-quark background rejections are evaluated using Monte Carlo simulation. Several benchmark tagging selections are defined for different signal efficiency targets. The modelling of the relevant input distributions used to tag Higgs bosons is studied in 36 fb- 1 of data collected in 2015 and 2016 using g→ bb¯ and Z(→ bb¯) γ event selections in data. Both processes are found to be well modelled within the statistical and systematic uncertainties. © 2019, CERN for the benefit of the ATLAS collaboration.
|
|
| 45. |
- Aad, G, et al.
(författare)
-
Jet energy scale and resolution measured in proton–proton collisions at √s=13 TeV with the ATLAS detector
- 2021
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 81:8
-
Tidskriftsartikel (refereegranskat)abstract
- Jet energy scale and resolution measurements with their associated uncertainties are reported for jets using 36–81 fb−1 of proton–proton collision data with a centre-of-mass energy of s√=13 TeV collected by the ATLAS detector at the LHC. Jets are reconstructed using two different input types: topo-clusters formed from energy deposits in calorimeter cells, as well as an algorithmic combination of charged-particle tracks with those topo-clusters, referred to as the ATLAS particle-flow reconstruction method. The anti-kt jet algorithm with radius parameter R=0.4 is the primary jet definition used for both jet types. This result presents new jet energy scale and resolution measurements in the high pile-up conditions of late LHC Run 2 as well as a full calibration of particle-flow jets in ATLAS. Jets are initially calibrated using a sequence of simulation-based corrections. Next, several in situ techniques are employed to correct for differences between data and simulation and to measure the resolution of jets. The systematic uncertainties in the jet energy scale for central jets (|η|<1.2) vary from 1% for a wide range of high-pT jets (2502.5 TeV). The relative jet energy resolution is measured and ranges from (24±1.5)% at 20 GeV to (6±0.5)% at 300 GeV.
|
|
| 46. |
- Aad, G., et al.
(författare)
-
Luminosity determination in pp collisions at √s=13 TeV using the ATLAS detector at the LHC
- 2023
-
Ingår i: European Physical Journal C. - : Institute for Ionics. - 1434-6044 .- 1434-6052. ; 83:10
-
Tidskriftsartikel (refereegranskat)abstract
- The luminosity determination for the ATLAS detector at the LHC during Run 2 is presented, with pp collisions at a centre-of-mass energy s=13 TeV. The absolute luminosity scale is determined using van der Meer beam separation scans during dedicated running periods in each year, and extrapolated to the physics data-taking regime using complementary measurements from several luminosity-sensitive detectors. The total uncertainties in the integrated luminosity for each individual year of data-taking range from 0.9% to 1.1%, and are partially correlated between years. After standard data-quality selections, the full Run 2 pp data sample corresponds to an integrated luminosity of 140.1 ± 1.2 fb - 1 , i.e. an uncertainty of 0.83%. A dedicated sample of low-pileup data recorded in 2017–2018 for precision Standard Model physics measurements is analysed separately, and has an integrated luminosity of 338.1 ± 3.1 pb - 1 . © 2023, The Author(s).
|
|
| 47. |
- Aad, G, et al.
(författare)
-
Measurement of distributions sensitive to the underlying event in inclusive Z boson production in pp collisions at √s = 13 TeV with the ATLAS detector
- 2019
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 79:8
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents measurements of charged-particle distributions sensitive to the properties of the underlying event in events containing a Z boson decaying into a muon pair. The data were obtained using the ATLAS detector at the LHC in proton–proton collisions at a centre-of-mass energy of 13 Te with an integrated luminosity of 3.2fb-1. Distributions of the charged-particle multiplicity and of the charged-particle transverse momentum are measured in regions of the azimuth defined relative to the Z boson direction. The measured distributions are compared with the predictions of various Monte Carlo generators which implement different underyling event models. The Monte Carlo model predictions qualitatively describe the data well, but with some significant discrepancies. © 2019, CERN for the benefit of the ATLAS collaboration.
|
|
| 48. |
- Aad, G, et al.
(författare)
-
Measurement of flow harmonics correlations with mean transverse momentum in lead–lead and proton–lead collisions at √sNN=5.02TeV with the ATLAS detector
- 2019
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 79:12
-
Tidskriftsartikel (refereegranskat)abstract
- To assess the properties of the quark–gluon plasma formed in ultrarelativistic ion collisions, the ATLAS experiment at the LHC measures a correlation between the mean transverse momentum and the flow harmonics. The analysis uses data samples of lead–lead and proton–lead collisions obtained at the centre-of-mass energy per nucleon pair of 5.02 TeV, corresponding to total integrated luminosities of 22μb-1 and 28nb-1, respectively. The measurement is performed using a modified Pearson correlation coefficient with the charged-particle tracks on an event-by-event basis. The modified Pearson correlation coefficients for the 2nd-, 3rd-, and 4th-order flow harmonics are measured in the lead–lead collisions as a function of event centrality quantified as the number of charged particles or the number of nucleons participating in the collision. The measurements are performed for several intervals of the charged-particle transverse momentum. The correlation coefficients for all studied harmonics exhibit a strong centrality evolution, which only weakly depends on the charged-particle momentum range. In the proton–lead collisions, the modified Pearson correlation coefficient measured for the 2nd-order flow harmonics shows only weak centrality dependence. The lead-lead data is qualitatively described by the predictions based on the hydrodynamical model.
|
|
| 49. |
- Aad, G, et al.
(författare)
-
Measurement of KS0 and Λ production in tt¯ dileptonic events in pp collisions at √s= 7 TeV with the ATLAS detector
- 2019
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 79:12
-
Tidskriftsartikel (refereegranskat)abstract
- Measurements of KS0 and Λ production in tt¯ final states have been performed. They are based on a data sample with integrated luminosity of 4.6 fb - 1 from proton–proton collisions at a centre-of-mass energy of 7 TeV, collected in 2011 with the ATLAS detector at the Large Hadron Collider. Neutral strange particles are separated into three classes, depending on whether they are contained in a jet, with or without a b-tag, or not associated with a selected jet. The aim is to look for differences in their main kinematic distributions. A comparison of data with several Monte Carlo simulations using different hadronisation and fragmentation schemes, colour reconnection models and different tunes for the underlying event has been made. The production of neutral strange particles in tt¯ dileptonic events is found to be well described by current Monte Carlo models for KS0 and Λ production within jets, but not for those produced outside jets. © 2019, CERN for the benefit of the ATLAS collaboration.
|
|
| 50. |
- Aad, G, et al.
(författare)
-
Measurement of single top-quark production in association with a W boson in the single-lepton channel at √s=8TeV with the ATLAS detector
- 2021
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 81:8
-
Tidskriftsartikel (refereegranskat)abstract
- The production cross-section of a top quark in association with a W boson is measured using proton–proton collisions at s√=8TeV. The dataset corresponds to an integrated luminosity of 20.2fb−1, and was collected in 2012 by the ATLAS detector at the Large Hadron Collider at CERN. The analysis is performed in the single-lepton channel. Events are selected by requiring one isolated lepton (electron or muon) and at least three jets. A neural network is trained to separate the tW signal from the dominant tt¯ background. The cross-section is extracted from a binned profile maximum-likelihood fit to a two-dimensional discriminant built from the neural-network output and the invariant mass of the hadronically decaying W boson. The measured cross-section is σtW=26±7pb, in good agreement with the Standard Model expectation.
|
|
