UVicSpace : Browsing by Author "Aaboud, M."

Browsing by Author "Aaboud, M."

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Analysis of the Wtb vertex from the measurement of triple-differential angular decay rates of single top quarks produced in the t-channel at root s=8 TeV with the ATLAS detector
(Journal of High Energy Physics, 2017) Aaboud, M.; Albert, Justin; Chiu, Y. H.; Elliot, Alison A.; Fincke-Keeler, J.; Hamano, Kenji; Hill, Ewan Chin; Keeler, Richard; Kowalewski, Robert; Kuwertz, E. S.; Kwan, Tony; LeBlanc, Matthew Edgar; Lefebvre, Michel; McPherson, Robert A.; Seuster, Rolf; Sobie, Randall J.; Trovatelli, M.; Venturi, M.; et al.
The electroweak production and subsequent decay of single top quarks in the t-channel is determined by the properties of the Wtb vertex, which can be described by the complex parameters of an effective Lagrangian. An analysis of a triple-differential decay rate in t-channel production is used to simultaneously determine five generalised helicity fractions and phases, as well as the polarisation of the produced top quark. The complex parameters are then constrained. This analysis is based on 20.2 fb(-1) of proton-proton collision data at a centre-of-mass energy of 8 TeV collected with the ATLAS detector at the LHC. The fraction of decays containing transversely polarised W bosons is measured to be f(1) = 0.30 +/- 0.05. The phase between amplitudes for transversely and longitudinally polarised W bosons recoiling against left-handed b-quarks is measured to be delta = 0.002 pi(+0.016 pi)(+0.017 pi), giving no indication of CP violation. The fractions of longitudinal or transverse W bosons accompanied by right-handed b-quarks are also constrained. Based on these measurements, limits are placed at 95% CL on the ratio of the complex coupling parameters Re [g(R)/V-L is an element of [-0.12, 0.17] and Im [g(R)/V-L is an element of [-0.07, 0.06]. Constraints are also placed on the ratios vertical bar V-R/V-L vertical bar and vertical bar g(L)/V-L vertical bar. In addition, the polarisation of single top quarks in the t-channel is constrained to be P > 0.72 (95% CL). None of the above measurements make assumptions about the value of any of the other parameters or couplings and all of them are in agreement with the Standard Model.
Combinations of single-top-quark production cross-section measurements and |fLVVtb| determinations at √s = 7 and 8 TeV with the ATLAS and CMS experiments
(Journal of High Energy Physics, 2019) Aaboud, M.; Aad, G.; Abbott, B.; Abbott, D.C.; Abdinov, O.; Abed Abud, A.; Abhayasinghe, D.K.; Abidi, S.H.; AbouZeid, O.S; Abraham, N.L; Albert, J; Anelli, C. R; Chiu, Y. H; Ghasemi Bostanabad, M; Hamano, K; Hill, E; Kay, E. F; Keeler, R; Kowalewski, R; Lefebvre, M; et al.
This paper presents the combinations of single-top-quark production crosssection measurements by the ATLAS and CMS Collaborations, using data from LHC proton–proton collisions at √ s = 7 and 8 TeV corresponding to integrated luminosities of 1.17 to 5.1 fb−1 at √ s = 7 TeV and 12.2 to 20.3 fb−1 at √ s = 8 TeV. These combinations are performed per centre-of-mass energy and for each production mode: tchannel, tW, and s-channel. The combined t-channel cross-sections are 67.5 ± 5.7 pb and 87.7 ± 5.8 pb at √ s = 7 and 8 TeV respectively. The combined tW cross-sections are 16.3 ± 4.1 pb and 23.1 ± 3.6 pb at √ s = 7 and 8 TeV respectively. For the schannel cross-section, the combination yields 4.9 ± 1.4 pb at √ s = 8 TeV. The square of the magnitude of the CKM matrix element Vtb multiplied by a form factor fLV is determined for each production mode and centre-of-mass energy, using the ratio of the measured cross-section to its theoretical prediction. It is assumed that the top-quark-related CKM matrix elements obey the relation |Vtd|, |Vts| |Vtb|. All the |fLVVtb| 2 determinations, extracted from individual ratios at √ s = 7 and 8 TeV, are combined, resulting in |fLVVtb| = 1.02 ± 0.04 (meas.) ± 0.02 (theo.). All combined measurements are consistent with their corresponding Standard Model predictions.
Constraints on mediator-based dark matter and scalar dark energy models using √s = 13 TeV pp collision data collected by the ATLAS detector
(Journal of High Energy Physics, 2019) Aaboud, M.; Aad, G.; Abbott, B.; Abbott, D.C.; Abdinov, O.; Abhayasinghe, D.K.; Abidi, S.H.; AbouZeid, O.S.; Abraham, N.L.; Abramowicz, H.; Albert, Justin; Anelli, Christopher R.; Chiu, Y. H.; Ghasemi Bostanabad, M.; Hamano, Kenji; Hill, Ewan Chin; Kay, E. F.; Keeler, Richard; Kowalewski, Robert; et al.
Constraints on selected mediator-based dark matter models and a scalar dark energy model using up to 37 fb−1 s√=13 TeV pp collision data collected by the ATLAS detector at the LHC during 2015-2016 are summarised in this paper. The results of experimental searches in a variety of final states are interpreted in terms of a set of spin-1 and spin-0 single-mediator dark matter simplified models and a second set of models involving an extended Higgs sector plus an additional vector or pseudo-scalar mediator. The searches considered in this paper constrain spin-1 leptophobic and leptophilic mediators, spin-0 colour-neutral and colour-charged mediators and vector or pseudo-scalar mediators embedded in extended Higgs sector models. In this case, also s√=8 TeV pp collision data are used for the interpretation of the results. The results are also interpreted for the first time in terms of light scalar particles that could contribute to the accelerating expansion of the universe (dark energy).
Determination of the strong coupling constant αs from transverse energy–energy correlations in multijet events at s√=8 TeV using the ATLAS detector
(The European Physical Journal C, 2017) Aaboud, M.; Albert, Justin; Chiu, Y. H.; Elliot, Alison A.; Fincke-Keeler, J.; Hamano, Kenji; Hill, Ewan Chin; Keeler, Richard; Kowalewski, Robert; Kuwertz, E. S.; Kwan, Tony; LeBlanc, Matthew Edgar; Lefebvre, Michel; McPherson, Robert A.; Seuster, Rolf; Sobie, Randall J.; Trovatelli, M.; Venturi, M.
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√=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 αs(μ) predicted in QCD up to scales over 1 TeV. A global fit to the transverse energy–energy correlation distributions yields αs(mZ)=0.1162±0.0011(exp.) +0.0084−0.0070(theo.) , while a global fit to the asymmetry distributions yields a value of αs(mZ)=0.1196±0.0013(exp.) +0.0075−0.0045(theo.) .
Electron efficiency measurements with the ATLAS detector using 2012 LHC proton-proton collision data
(The European Physical Journal C, 2017) Aaboud, M.; Albert, Justin; Elliot, Alison A.; Fincke-Keeler, J.; Hamano, Kenji; Hill, Ewan Chin; Keeler, Richard; Kowalewski, Robert; Kuwertz, E. S.; Kwan, Tony; LeBlanc, Matthew Edgar; Lefebvre, Michel; McPherson, Robert A.; Pearce, James D.; Seuster, Rolf; Sobie, Randall J.; Trovatelli, M.; Venturi, M.; ATLAS Collaboration
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 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→eeγ and J/ψ→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 ET=15 GeV and 99% at ET=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.
Electron reconstruction and identification in the ATLAS experiment using the 2015 and 2016 LHC proton–proton collision data at √s =13 TeV
(The European Physical Journal C, 2019) Aaboud, M.; Aad, G.; Abbott, B.; Abbott, D.C.; Abdinov, O.; Abeloos, B.; Abhayasinghe, D.K.; Abidi, S.H.; AbouZeid, O.S.; Abraham, N.L.; Albert, Justin; Anelli, Christopher R.; Chiu, Y.H.; Ghasemi Bostanabad, M.; Hamano, Kenji; Hill, Ewan Chin; Keeler, Richard; Kowalewski, Robert; Lefebvre, Michel; et al.
Algorithms used for the reconstruction and identification of electrons in the central region of the ATLAS detector at the Large Hadron Collider (LHC) are presented in this paper; these algorithms are used in ATLAS physics analyses that involve electrons in the final state and which are based on the 2015 and 2016 proton–proton collision data produced by the LHC at s√ = 13 TeV. The performance of the electron reconstruction, identification, isolation, and charge identification algorithms is evaluated in data and in simulated samples using electrons from Z→ee and J/ψ→ee decays. Typical examples of combinations of electron reconstruction, identification, and isolation operating points used in ATLAS physics analyses are shown.
Erratum to: Measurement of differential cross sections and W+/W− cross-section ratios for W boson production in association with jets at s√ = 8 TeV with the ATLAS detector
(Journal of High Energy Physics, 2020) Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.; Abeloos, B.; Abidi, S.H.; AbouZeid, O.S.; Abraham, N.L.; Abramowicz, H.; Abreu, H.; Albert, Justin; Chiu, Y. H.; Elliot, Alison A.; Fincke-Keeler, M.; Hamano, Kenji; Hill, Ewan Chin; Keeler, Richard; Kowalewski, Robert; Kuwertz, E. S.; Kwan, Tony; et al.
Erratum to: Measurement of the W boson polarisation in tt¯ events from pp collisions at s√=8 TeV in the lepton + jets channel with ATLAS
(The European Physical Journal C, 2019) Aaboud, M.; Aad, G.; Abbott, B.; Abdallah, J.; Abdinov, O.; Abeloos, B.; AbouZeid, O.S.; Abraham, N.L.; Abramowicz, H.; Abreu, H.; Albert, Justin; Elliot, Alison A.; Fincke-Keeler, M.; Hamano, Kenji; Hill, Ewan Chin; Keeler, Richard; Kowalewski, Robert; Kuwertz, E. S.; Kwan, Tony; et al.
Erratum to: Measurements of W and Z boson production in pp collisions at s√=5.02 TeV with the ATLAS detector
(The European Physical Journal C, 2019) Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.; Abeloos, B.; Abhayasinghe, D.K.; Abidi, S.H.; AbouZeid, O.S.; Abraham, N.L.; Abramowicz, H.; Albert, Justin; Anelli, Christopher R.; Chiu, Y.H.; Ghasemi Bostanabad, M.; Hamano, Kenji; Hill, Ewan Chin; Keeler, Richard; Kowalewski, Robert; Lefebvre, Michel; McLean, K.D.; et al.
Erratum: Search for supersymmetry in final states with two same-sign or three leptons and jets using 36 fb−1 of √ s = 13 TeV pp collision data with the ATLAS detector
(Journal of High Energy Physics, 2019) Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.; Abeloos, B.; Abidi, S.H.; AbouZeid, O.S.; Abraham, N.L.; Abramowicz, H.; Abreu, H.; Albert, Justin; Chiu, Y. H.; Elliot, Alison A.; Fincke-Keeler, J.; Hamano, Kenji; Hill, Ewan Chin; Keeler, Richard; Kowalewski, Robert; Kuwertz, E. S.; et al.
Evidence for light-by-light scattering in heavy-ion collisions with the ATLAS detector at the LHC
(Nature Physics, 2017) Aaboud, M.; Albert, Justin; Chiu, Y. H.; Elliot, Alison A.; Fincke-Keeler, J.; Hamano, Kenji; Hill, Ewan Chin; Keeler, Richard; Kowalewski, Robert; Kuwertz, E. S.; Kwan, Tony; LeBlanc, Matthew Edgar; Lefebvre, Michel; McPherson, Robert A.; Pearce, James D.; Seuster, Rolf; Sobie, Randall J.; Trovatelli, M.; Venturi, M.; ATLAS Collaboration
Light-by-light scattering (γγ → γγ) is a quantum-mechanical process that is forbidden in the classical theory of electrodynamics. This reaction is accessible at the Large Hadron Collider thanks to the large electromagnetic field strengths generated by ultra-relativistic colliding lead ions. Using 480 μb−1 of lead–lead collision data recorded at a centre-of-mass energy per nucleon pair of 5.02 TeV by the ATLAS detector, here we report evidence for light-by-light scattering. A total of 13 candidate events were observed with an expected background of 2.6 ± 0.7 events. After background subtraction and analysis corrections, the fiducial cross-section of the process Pb + Pb (γγ) → Pb(∗) + Pb(∗)γγ, for photon transverse energy ET > 3 GeV, photon absolute pseudorapidity |η| < 2.4, diphoton invariant mass greater than 6 GeV, diphoton transverse momentum lower than 2 GeV and diphoton acoplanarity below 0.01, is measured to be 70 ± 24 (stat.) ± 17 (syst.) nb, which is in agreement with the standard model predictions.
Evidence for the H -> b(b)over-bar decay with the ATLAS detector
(Journal of High Energy Physics, 2017) ATLAS Collaboration; Aaboud, M.; Albert, Justin; Chiu, Y. H.; Elliot, Alison A.; Fincke-Keeler, J.; Hamano, Kenji; Hill, Ewan Chin; Keeler, Richard; Kowalewski, Robert; Kuwertz, E. S.; Kwan, Tony; LeBlanc, Matthew Edgar; Lefebvre, Michel; McPherson, Robert A.; Seuster, Rolf; Sobie, Randall J.; Trovatelli, M.; Venturi, M.; et al.
A search for the decay of the Standard Model Higgs boson into a b (b) over bar pair when produced in association with a W or Z boson is performed with the ATLAS detector. The analysed data, corresponding to an integrated luminosity of 36.1 fb(-1), were collected in proton-proton collisions in Run 2 of the Large Hadron Collider at a centre-of-mass energy of 13 TeV. Final states containing zero, one and two charged leptons (electrons or muons) are considered, targeting the decays Z -> vv, W -> lv and Z -> ll. For a Higgs boson mass of 125 GeV, an excess of events over the expected background from other Standard Model processes is found with an observed significance of 3.5 standard deviations, compared to an expectation of 3.0 standard deviations. This excess provides evidence for the Higgs boson decay into b-quarks and for its production in association with a vector boson. The combination of this result with that of the Run 1 analysis yields a ratio of the measured signal events to the Standard Model expectation equal to 0.90 +/- 0.18(stat.)(-0.19)(+0.21)(syst.). Assuming the Standard Model production cross-section, the results are consistent with the value of the Yukawa coupling to b-quarks in the Standard Model.
Femtoscopy with identified charged pions in proton-lead collisions at root s(NN)=5.02 TeV with ATLAS
(Physical Review C, 2017) Aaboud, M.; Albert, Justin; David, Claire; Elliot, Alison A.; Fincke-Keeler, J.; Hamano, Kenji; Hill, Ewan Chin; Keeler, Richard; Kowalewski, Robert; Kuwertz, E. S.; Kwan, Tony; LeBlanc, Matthew Edgar; Lefebvre, Michel; McPherson, Robert A.; Pearce, James D.; Seuster, Rolf; Sobie, Randall J.; Trovatelli, M.; Venturi, M.; et al.
Bose-Einstein correlations between identified charged pions are measured for p+Pb collisions at √sNN=5.02TeV using data recorded by the ATLAS detector at the CERN Large Hadron Collider corresponding to a total integrated luminosity of 28nb−1. Pions are identified using ionization energy loss measured in the pixel detector. Two-particle correlation functions and the extracted source radii are presented as a function of collision centrality as well as the average transverse momentum (kT) and rapidity (y★ππ) of the pair. Pairs are selected with a rapidity −2
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
(The European Physical Journal C, 2017) Aaboud, M.; Albert, Justin; Elliot, Alison A.; Fincke-Keeler, J.; Hamano, Kenji; Hill, Ewan Chin; Keeler, Richard; Kowalewski, Robert; Kuwertz, E. S.; Kwan, Tony; LeBlanc, Matthew Edgar; Lefebvre, Michel; McPherson, Robert A.; Pearce, James D.; Seuster, Rolf; Sobie, Randall J.; Trovatelli, M.; Venturi, M.; et al.; ATLAS Collaboration
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 \(\sigma _{\text {tot}} (tq) = 56.7^{+4.3}_{-3.8}\;\mathrm{pb}\) for top-quark production and \(\sigma _{\text {tot}} (\bar{t} q) = 32.9^{+3.0}_{-2.7}\;\mathrm{pb}\) 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 \(R_t=1.72 \pm 0.09\). 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.
Fluctuations of anisotropic flow in Pb+Pb collisions at √sNN= 5.02 TeV with the ATLAS detector
(Journal of High Energy Physics, 2020) Aaboud, M.; Aad, G.; Abbott, B.; Abbott, D.C.; Abdinov, O.; Abed Abud, A.; Abhayasinghe, D.K.; Abidi, S.H.; AbouZeid, O.S.; Abraham, N.L.; Albert, Justin; Anelli, Christopher R.; Carlson, Evan Michael; Chiu, Y. H.; Ghasemi Bostanabad, M.; Hamano, Kenji; Kay, E. F.; Keeler, Richard; Kowalewski, Robert; Lefebvre, Michel; et al.
Multi-particle azimuthal cumulants are measured as a function of centrality and transverse momentum using 470 μb−1 of Pb+Pb collisions at sNN−−−√ = 5.02 TeV with the ATLAS detector at the LHC. These cumulants provide information on the event-by-event fluctuations of harmonic flow coefficients vn and correlated fluctuations between two harmonics vn and vm. For the first time, a non-zero four-particle cumulant is observed for dipolar flow, v1. The four-particle cumulants for elliptic flow, v2, and triangular flow, v3, exhibit a strong centrality dependence and change sign in ultra-central collisions. This sign change is consistent with significant non-Gaussian fluctuations in v2 and v3. The four-particle cumulant for quadrangular flow, v4, is found to change sign in mid-central collisions. Correlations between two harmonics are studied with three- and four-particle mixed-harmonic cumulants, which indicate an anti-correlation between v2 and v3, and a positive correlation between v2 and v4. These correlations decrease in strength towards central collisions and either approach zero or change sign in ultra-central collisions. To investigate the possible flow fluctuations arising from intrinsic centrality or volume fluctuations, the results are compared between two different event classes used for centrality definitions. In peripheral and mid-central collisions where the cumulant signals are large, only small differences are observed. In ultra-central collisions, the differences are much larger and transverse momentum dependent. These results provide new information to disentangle flow fluctuations from the initial and final states, as well as new insights on the influence of centrality fluctuations.
High-ET isolated-photon plus jets production in pp collisions at √s=8TeV with the ATLAS detector
(Nuclear Physics B, 2017) Aaboud, M.; Albert, Justin; Elliot, Alison A.; Fincke-Keeler, J.; Hamano, Kenji; Hill, Ewan Chin; Keeler, Richard; Kowalewski, Robert; Kuwertz, E. S.; Kwan, Tony; LeBlanc, Matthew Edgar; Lefebvre, Michel; McPherson, Robert A.; Pearce, James D.; Seuster, Rolf; Sobie, Randall J.; Trovatelli, M.; Venturi, M.; ATLAS Collaboration; et al
The dynamics of isolated-photon plus one-, two- and three-jet production in pp collisions at a centre-of-mass energy of 8 TeV are studied with the ATLAS detector at the LHC using a data set with an integrated luminosity of . Measurements of isolated-photon plus jets cross sections are presented as functions of the photon and jet transverse momenta. The cross sections as functions of the azimuthal angle between the photon and the jets, the azimuthal angle between the jets, the photon–jet invariant mass and the scattering angle in the photon–jet centre-of-mass system are presented. The pattern of QCD radiation around the photon and the leading jet is investigated by measuring jet production in an annular region centred on each object; enhancements are observed around the leading jet with respect to the photon in the directions towards the beams. The experimental measurements are compared to several different theoretical calculations, and overall a good description of the data is found.
Identification and rejection of pile-up jets at high pseudorapidity with the ATLAS detector
(The European Physical Journal C, 2017) Aaboud, M.; Albert, Justin; Chiu, Y. H.; Elliot, Alison A.; Fincke-Keeler, J.; Hamano, Kenji; Hill, Ewan Chin; Keeler, Richard; Kowalewski, Robert; Kuwertz, E. S.; Kwan, Tony; LeBlanc, Matthew Edgar; Lefebvre, Michel; McPherson, Robert A.; Seuster, Rolf; Sobie, Randall J.; Trovatelli, M.; Venturi, M.; et al.; ATLAS Collaboration
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 \(|\eta |>2.5\). 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 \(\,\text {TeV}\) collected with the ATLAS detector. The fraction of pile-up jets rejected in the range \(2.5<|\eta |<4.5\) 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.
In situ calibration of large-radius jet energy and mass in 13 TeV proton–proton collisions with the ATLAS detector
(The European Physical Journal C, 2019) Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.; Abeloos, B.; Abhayasinghe, D.K.; Abidi, S.H.; AbouZeid, O.S.; Abraham, N.L.; Abramowicz, H.; Albert, Justin; Anelli, Christopher R.; Chiu, Y. H.; Ghasemi Bostanabad, M.; Hamano, Kenji; Hill, Ewan Chin; Keeler, Richard; Kowalewski, Robert; Lefebvre, Michel; et al.
The response of the ATLAS detector to large-radius jets is measured in situ using 36.2 fb−1 of s√=13 TeV proton–proton collisions provided by the LHC and recorded by the ATLAS experiment during 2015 and 2016. The jet energy scale is measured in events where the jet recoils against a reference object, which can be either a calibrated photon, a reconstructed Z boson, or a system of well-measured small-radius jets. The jet energy resolution and a calibration of forward jets are derived using dijet balance measurements. The jet mass response is measured with two methods: using mass peaks formed by W bosons and top quarks with large transverse momenta and by comparing the jet mass measured using the energy deposited in the calorimeter with that using the momenta of charged-particle tracks. The transverse momentum and mass responses in simulations are found to be about 2–3% higher than in data. This difference is adjusted for with a correction factor. The results of the different methods are combined to yield a calibration over a large range of transverse momenta (pT). The precision of the relative jet energy scale is 1–2% for 200 GeV < pT < 2 TeV, while that of the mass scale is 2–10%. The ratio of the energy resolutions in data and simulation is measured to a precision of 10–15% over the same pT range.
Jet energy scale measurements and their systematic uncertainties in proton-proton collisions at √s=13 TeV with the ATLAS detector
(Physical Review D, 2017) Aaboud, M.; Albert, Justin; Chiu, Y. H.; Elliot, Alison A.; Fincke-Keeler, J.; Hamano, Kenji; Hill, Ewan Chin; Keeler, Richard; Kowalewski, Robert; Kuwertz, E. S.; Kwan, Tony; LeBlanc, Matthew Edgar; Lefebvre, Michel; McPherson, Robert A.; Seuster, Rolf; Sobie, Randall J.; Trovatelli, M.; Venturi, M.; et al.; ATLAS Collaboration
Jet energy scale measurements and their systematic uncertainties are reported for jets measured with the ATLAS detector using proton-proton collision data with a center-of-mass energy of √s=13 TeV, corresponding to an integrated luminosity of 3.2 fb−1 collected during 2015 at the LHC. Jets are reconstructed from energy deposits forming topological clusters of calorimeter cells, using the anti-kt algorithm with radius parameter R=0.4. Jets are calibrated with a series of simulation-based corrections and in situ techniques. In situ techniques exploit the transverse momentum balance between a jet and a reference object such as a photon, Z boson, or multijet system for jets with 200.8) is derived from dijet pT balance measurements. For jets of pT=80 GeV, the additional uncertainty for the forward jet calibration reaches its largest value of about 2% in the range |η|>3.5 and in a narrow slice of 2.2<|η|<2.4.
Jet reconstruction and performance using particle flow with the ATLAS Detector
(The European Physical Journal C, 2017) Aaboud, M.; Albert, Justin; Chiu, Y. H.; Elliot, Alison A.; Fincke-Keeler, J.; Hamano, Kenji; Hill, Ewan Chin; Keeler, Richard; Kowalewski, Robert; Kuwertz, E. S.; Kwan, Tony; LeBlanc, Matthew Edgar; Lefebvre, Michel; McPherson, Robert A.; Pearce, James D.; Seuster, Rolf; Sobie, Randall J.; Trovatelli, M.; Venturi, M.; ATLAS Collaboration
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.

Browsing by Author "Aaboud, M."

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