Izen, Joseph M.

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Dr. Izen is an high energy particle physics experimentalist exploring high-energy proton collisions produced at CERN's Large Hadron collider and electron-positron collisions at the Stanford Linear Accelerator Center (SLAC) . He is Principal Investigator of a Department of Energy grant supporting the UT Dallas' High Energy Physics Group work on the ATLAS and BaBar experiments.

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Recent Submissions

Now showing 1 - 20 of 428
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    Measurement of Angular and Momentum Distributions of Charged Particles within and Around Jets in Pb+Pb and pp Collisions at √{sₙₙ} = 5.02 TeV with ATLAS at the LHC
    (Elsevier Science B.V., 2019-01-22) Puri, Akshat; Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.; Abeloos, B.; Abhayasinghe, D. K.; Abidi, S. H.; Izen, Joseph M.; Meirose, Bernhard; Reeves, Kendall; ATLAS Collaboration; 250674117 (Izen, JM); Izen, Joseph M.; Meirose, Bernhard; Reeves, Kendall
    Studies of the fragmentation of jets into charged particles in heavy-ion collisions can help in understanding the mechanism of jet quenching by the hot and dense QCD matter created in such collisions, the quark-gluon plasma. These proceedings present a measurement of the angular distribution of charged particles around the jet axis in √{sₙₙ} = 5.02 TeV Pb+Pb and pp collisions, done using the ATLAS detector at the LHC. The measurement is performed inside jets reconstructed with the anti-kₜ algorithm with radius parameter R = 0.4, and is extended to regions outside the jet cone. Results are presented as a function of Pb+Pb collision centrality, and both jet and charged-particle transverse momenta.
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    Measurement of Heavy Flavor Production and Azimuthal Anisotropy in Small and Large Systems with ATLAS
    (Elsevier Science B.V., 2019-02) Hu, Qipeng; Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.; Abeloos, B.; Abhayasinghe, D. K.; Abidi, S. H.; Izen, Joseph M.; Meirose, Bernhard; Reeves, Kendall; ATLAS Collaboration; 250674117 (Izen, JM); Izen, Joseph M.; Meirose, Bernhard; Reeves, Kendall
    Heavy-flavor hadron production and collective motion in A+A collisions provide insight into the energy loss mechanism and transport properties of heavy quarks in the QGP. The same measurements in p+A collisions serve as an important baseline for understanding the observations in A+A collisions. For example, detailed studies of heavy-flavor hadron azimuthal anisotropy in p+A collisions may help to address whether the observed long-range "ridge" correlation arises from hard or semi-hard processes, or if it is the result of mechanisms unrelated to the initial hardness scale. These proceedings summarize heavy-flavor hadron production, via their semi-leptonic decay to muons in 2.76 TeV Pb+Pb and pp collisions, non-prompt J/ψ in 5.02 TeV Pb+Pb and pp collisions, and prompt D⁰ mesons in 8.16 TeV p+Pb collisions using ATLAS detector at the LHC. Azimuthal anisotropy of heavy-flavor hadrons is studied via their decay muons in 2.76 TeV Pb+Pb and 8.16 TeV p+Pb collisions, and via non-prompt J/ψ in 5.02 TeV Pb+Pb collisions. Strong suppression of heavy-flavor hadron production and azimuthal anisotropy are observed in Pb+Pb collisions, while significant azimuthal anisotropy of heavy-flavor muons is observed in p+Pb collisions, without evidence of the modification of their production rates.
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    Search for Light Resonances Decaying to Boosted Quark Pairs and Produced in Association with a Photon or a Jet in Proton-Proton Collisions at √s=13 TeV with the ATLAS Detector
    (Elsevier Science B.V., 2018-11-02) Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.; Abeloos, B.; Abidi, S. H.; Abouzeid, O. S.; Izen, Joseph M.; Meirose, Bernhard; Reeves, Kendall; ATLAS Collaboration; 250674117 (Izen, JM); Izen, Joseph M.; Meirose, Bernhard; Reeves, Kendall
    This Letter presents a search for new light resonances decaying to pairs of quarks and produced in association with a high-p_{T} photon or jet. The dataset consists of proton-proton collisions with an integrated luminosity of 36.1 fb⁻¹ at a centre-of-mass energy of √s = 13 TeV recorded by the ATLAS detector at the Large Hadron Collider. Resonance candidates are identified as massive large-radius jets with substructure consistent with a particle decaying into a quark pair. The mass spectrum of the candidates is examined for local excesses above background. No evidence of a new resonance is observed in the data, which are used to exclude the production of a lepto-phobic axial-vector Z′ boson.
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    Search for Vector-Boson Resonances Decaying to a Top Quark and Bottom Quark in the Lepton Plus Jets Final State in pp Collisions at √s=13 TeV with the ATLAS Detector
    (Elsevier Science B.V., 2018-11-22) Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.; Abeloos, B.; Abhayasinghe, D. K.; Abidi, S. H.; Izen, Joseph M.; Meirose, Bernhard; Reeves, Kendall; ATLAS Collaboration; 250674117 (Izen, JM); Izen, Joseph M.; Meirose, Bernhard; Reeves, Kendall
    A search for new charged massive gauge bosons, W′, is performed with the ATLAS detector at the LHC. Data were collected in proton-proton collisions at a center-of-mass energy of √s = 13 TeV and correspond to an integrated luminosity of 36.1 fb⁻¹. This analysis searches for W′ bosons in the W′ > tb̅ decay channel in final states with an electron or muon plus jets. The search covers resonance masses between 0.5 and 5.0 TeV and considers right-handed W′ bosons. No significant deviation from the Standard Model (SM) expectation is observed and upper limits are set on the W′ > tb̅ cross section times branching ratio and the W′ boson effective couplings as a function of the W′ boson mass. For right-handed W′ bosons with coupling to the SM particles equal to the SM weak coupling constant, masses below 3.15 TeV are excluded at the 95% confidence level. This search is also combined with a previously published ATLAS result for W′ > tb̅ in the fully hadronic final state. Using the combined searches, right-handed W′ bosons with masses below 3.25 TeV are excluded at the 95% confidence level.
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    Search for Squarks and Gluinos in Final States with Hadronically Decaying Tau-Leptons, Jets, and Missing Transverse Momentum using pp Collisions at √s = 13 TeV with the ATLAS Detector
    (Amer Physical Soc, 2019-01-18) Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.; Abeloos, B.; Abhayasinghe, D. K.; Abidi, S. H.; Izen, Joseph M.; Meirose, Bernhard; Reeves, Kendall; ATLAS Collaboration; 250674117 (Izen, JM); Izen, Joseph M.; Meirose, Bernhard; Reeves, Kendall
    A search for supersymmetry in events with large missing transverse momentum, jets, and at least one hadronically decaying tau-lepton is presented. Two exclusive final states with either exactly one or at least two tau-leptons are considered. The analysis is based on proton-proton collisions at √s = 13 TeV corresponding to an integrated luminosity of 36.1 fb⁻¹ delivered by the Large Hadron Collider and recorded by the ATLAS detector in 2015 and 2016. No significant excess is observed over the Standard Model expectation. At 95% confidence level, model-independent upper limits on the cross section are set and exclusion limits are provided for two signal scenarios: a simplified model of gluino pair production with tau-rich cascade decays, and a model with gauge-mediated supersymmetry breaking (GMSB). In the simplified model, gluino masses up to 2000 GeV are excluded for low values of the mass of the lightest supersymmetric particle (LSP), while LSP masses up to 1000 GeV are excluded for gluino masses around 1400 GeV. In the GMSB model, values of the supersymmetry-breaking scale are excluded below 110 TeV for all values of tan β in the range 2 ≤ tan β ≤ 60, and below 120 TeV for tan β > 30.
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    Search for Pairs of Highly Collimated Photon-Jets in pp Collisions at √s=13 TeV with the ATLAS Detector
    (Amer Physical Soc, 2019-01-18) Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.; Abeloos, B.; Abhayasinghe, D. K.; Abidi, S. H.; Izen, Joseph M.; Meirose, Bernhard; Reeves, Kendall; ATLAS Collaboration; 250674117 (Izen, JM); Izen, Joseph M.; Meirose, Bernhard; Reeves, Kendall
    Results of a search for the pair production of photon-jets—collimated groupings of photons—in the ATLAS detector at the Large Hadron Collider are reported. Highly collimated photon-jets can arise from the decay of new, highly boosted particles that can decay to multiple photons collimated enough to be identified in the electromagnetic calorimeter as a single, photonlike energy cluster. Data from proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 36.7 fb⁻¹, were collected in 2015 and 2016. Candidate photon-jet pair production events are selected from those containing two reconstructed photons using a set of identification criteria much less stringent than that typically used for the selection of photons, with additional criteria applied to provide improved sensitivity to photon-jets. Narrow excesses in the reconstructed diphoton mass spectra are searched for. The observed mass spectra are consistent with the Standard Model background expectation. The results are interpreted in the context of a model containing a new, high-mass scalar particle with narrow width, X, that decays into pairs of photon-jets via new, light particles, α. Upper limits are placed on the cross section times the product of branching ratios σ × ℬ(X → αα) × ℬ(α → γγ)² for 200  GeV < mX < 2  TeV and for ranges of m_α from a lower mass of 100 MeV up to between 2 and 10 GeV, depending upon m_X. Upper limits are also placed on σ × ℬ(X → αα) × ℬ(α → 3π⁰)² for the same range of m_X and for ranges of m_α from a lower mass of 500 MeV up to between 2 and 10 GeV.
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    Search for Doubly Charged Scalar Bosons Decaying into Same-Sign W Boson Pairs with the ATLAS Detector
    (Springer, 2019-01-23) Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.; Abeloos, B.; Abhayasinghe, D. K.; Abidi, S. H.; Izen, Joseph M.; Meirose, Bernhard; Reeves, Kendall; ATLAS Collaboration; 250674117 (Izen, JM); Izen, Joseph M.; Meirose, Bernhard; Reeves, Kendall
    A search for doubly charged scalar bosons decaying into W boson pairs is presented. It uses a data sample from proton-proton collisions corresponding to an integrated luminosity of 36.1 fb⁻¹ collected by the ATLAS detector at the LHC at a centre-of-mass energy of 13 TeV in 2015 and 2016. This search is guided by a model that includes an extension of the Higgs sector through a scalar triplet, leading to a rich phenomenology that includes doubly charged scalar bosons H^{±±}. Those bosons are produced in pairs in proton-proton collisions and decay predominantly into electroweak gauge bosons H^{±±} → W^{±}W^{±}. Experimental signatures with several leptons, missing transverse energy and jets are explored. No significant deviations from the Standard Model predictions are found. The parameter space of the benchmark model is excluded at 95% confidence level for H^{±±} bosons with masses between 200 and 220 GeV.
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    Search for Pair Production of Higgs Bosons in the bb̅bb̅ Final State using Proton-Proton Collisions at √s=13 TeV with the ATLAS Detector
    (Springer, 2019-01-03) Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.; Abeloos, B.; Abidi, S. H.; AbouZeid, O. S.; Izen, Joseph M.; Meirose, Bernhard; Reeves, Kendall; ATLAS Collabration; 250674117 (Izen, JM); Izen, Joseph M.; Meirose, Bernhard; Reeves, Kendall
    A search for Higgs boson pair production in the bb̅bb̅ final state is carried out with up to 36.1 fb⁻¹ of LHC proton-proton collision data collected at √s=13 TeV with the ATLAS detector in 2015 and 2016. Three benchmark signals are studied: a spin-2 graviton decaying into a Higgs boson pair, a scalar resonance decaying into a Higgs boson pair, and Standard Model non-resonant Higgs boson pair production. Two analyses are carried out, each implementing a particular technique for the event reconstruction that targets Higgs bosons reconstructed as pairs of jets or single boosted jets. The resonance mass range covered is 260-3000 GeV. The analyses are statistically combined and upper limits on the production cross section of Higgs boson pairs times branching ratio to bb̅bb̅ are set in each model. No significant excess is observed; the largest deviation of data over prediction is found at a mass of 280 GeV, corresponding to 2.3 standard deviations globally. The observed 95% confidence level upper limit on the non-resonant production is 13 times the Standard Model prediction.
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    Search for Long-Lived Particles in Final States with Displaced Dimuon Vertices in PP Collisions at √s=13 TeV with the ATLAS Detector
    (Amer Physical Soc, 2019-01-03) Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.; Abeloos, B.; Abhayasinghe, D. K.; Abidi, S. H.; Izen, Joseph M.; Meirose, Bernhard; Reeves, Kendall; ATLAS Collaboration; 250674117 (Izen, JM); Izen, Joseph M.; Meirose, Bernhard; Reeves, Kendall
    A search is performed for a long-lived particle decaying into a final state that includes a pair of muons of opposite-sign electric charge, using proton-proton collision data collected at √s = 13 TeV by the ATLAS detector at the Large Hadron Collider corresponding to an integrated luminosity of 32.9 fb⁻¹. No significant excess over the Standard Model expectation is observed. Limits at 95% confidence level on the lifetime of the long-lived particle are presented in models of new phenomena including gauge-mediated supersymmetry or decay of the Higgs boson, H, to a pair of dark photons, Z_{D}. Lifetimes in the range cτ = 1-2400 cm are excluded, depending on the parameters of the model. In the supersymmetric model, the lightest neutralino is the next-to-lightest supersymmetric particle, with a relatively long lifetime due to its weak coupling to the gravitino, the lightest supersymmetric particle. The lifetime limits are determined for very light gravitino mass and various assumptions for the neutralino mass in the range 300-1000 GeV. In the dark photon model, the lifetime limits are interpreted as exclusion contours in the plane of the coupling between the Z_{D} and the Standard Model Z boson versus the Z_{D} mass (in the range 20-60 GeV), for various assumptions for the H -> Z_{D}Z_{D} branching fraction.
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    Search for Heavy Majorana or Dirac Neutrinos and Right-Handed W Gauge Bosons in Final States with Two Charged Leptons and Two Jets at √s=13 TeV with the ATLAS Detector
    (Springer, 2019-01) Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.; Abeloos, B.; Abhayasinghe, D. K.; Abidi, S. H.; Izen, Joseph M.; Meirose, Bernhard; Reeves, Kendall; ATLAS Collaboration; 250674117 (Izen, JM); Izen, Joseph M.; Meirose, Bernhard; Reeves, Kendall
    A search for heavy right-handed Majorana or Dirac neutrinos N_{R} and heavy right-handed gauge bosons W_{R} is performed in events with a pair of energetic electrons or muons, with the same or opposite electric charge, and two energetic jets. The events are selected from pp collision data with an integrated luminosity of 36.1 fb⁻¹ collected by the ATLAS detector at TeV. No significant deviations from the Standard Model are observed. The results are interpreted within the theoretical framework of a left-right symmetric model and lower limits are set on masses in the heavy right-handed W boson and neutrino mass plane. The excluded region extends to TeV for both Majorana and Dirac N_{R} neutrinos.
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    Search for Heavy Charged Long-Lived Particles in Proton-Proton Collisions at √s=13 TeV Using an Ionisation Measurement with the ATLAS Detector
    (Elsevier Science BV, 2019-01-10) Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.; Abeloos, B.; Abhayasinghe, D. K.; Abidi, S. H.; Izen, Joseph M.; Meirose, Bernhard; Reeves, Kendall; ATLAS Collaboration; 250674117 (Izen, JM); Izen, Joseph M.; Meirose, Bernhard; Reeves, Kendall
    This Letter presents a search for heavy charged long-lived particles produced in proton-proton collisions at √s= 13 TeV at the LHC using a data sample corresponding to an integrated luminosity of 36.1 fb⁻¹ collected by the ATLAS experiment in 2015 and 2016. These particles are expected to travel with a velocity significantly below the speed of light, and therefore have a specific ionisation higher than any high-momentum Standard Model particle of unit charge. The pixel subsystem of the ATLAS detector is used in this search to measure the ionisation energy loss of all reconstructed charged particles which traverse the pixel detector. Results are interpreted assuming the pair production of R-hadrons as composite colourless states of a long-lived gluino and Standard Model partons. No significant deviation from Standard Model background expectations is observed, and lifetime-dependent upper limits on R-hadron production cross-sections and gluino masses are set, assuming the gluino always decays to two quarks and a 100 GeV stable neutralino. R-hadrons with lifetimes above 1.0 ns are excluded at the 95% confidence level, with lower limits on the gluino mass ranging between 1290 GeV and 2060 GeV. In the case of stable R-hadrons, the lower limit on the gluino mass at the 95% confidence level is 1890 GeV.
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    Search for Single Production of Vector-Like Quarks Decaying into Wb in pp Collisions at √s = 13 TeV with the ATLAS Detector
    (Springer Verlag, 2019-05-27) Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.; Abeloos, B.; Abhayasinghe, D. K.; Abidi, S. H.; Izen, Joseph M.; Meirose, Bernhard; Reeves, Kendall; ATLAS collaboration; 250674117 (Izen, JM); Izen, Joseph M.; Meirose, Bernhard; Reeves, Kendall
    A search for singly produced vector-like quarks Q, where Q can be either a T quark with charge +2/3 or a Y quark with charge −4/3, is performed in proton–proton collision data at a centre-of-mass energy of 13 TeV corresponding to an integrated luminosity of 36.1 fb⁻¹, recorded with the ATLAS detector at the LHC in 2015 and 2016. The analysis targets Q → Wb decays where the W boson decays leptonically. No significant deviation from the expected Standard Model background is observed. Upper limits are set on the QWb coupling strength and the mixing between the Standard Model sector and a singlet T quark or a Y quark from a (B, Y) doublet or a (T, B, Y) triplet, taking into account the interference effects with the Standard Model background. The upper limits set on the mixing angle are as small as |sin θ_{L}| = 0.18 for a singlet T quark of mass 800 GeV, |sin θ_{R}| = 0.17 for a Y quark of mass 800 GeV in a (B, Y) doublet model and |sin θ_{L}| = 0.16 for a Y quark of mass 800 GeV in a (T, B, Y) triplet model. Within a (B, Y) doublet model, the limits set on the mixing parameter |sin θ_{R}| are comparable with the exclusion limits from electroweak precision observables in the mass range between about 900 GeV and 1250 GeV. © 2019, The Author(s).
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    Search for Higgs Boson Pair Production in the WW*WW* Decay Channel Using ATLAS Data Recorded at √s = 13 TeV
    (Springer Verlag, 2019-05-21) Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.; Abeloos, B.; Abhayasinghe, D. K.; Abidi, S. H.; Izen, Joseph M.; Meirose, Bernhard; Reeves, Kendall; ATLAS collaboration; 250674117 (Izen, JM); Izen, Joseph M.; Meirose, Bernhard; Reeves, Kendall
    A search for a pair of neutral, scalar bosons with each decaying into two W bosons is presented using 36.1 fb⁻¹ of proton-proton collision data at a centre-of-mass energy of 13 TeV recorded with the ATLAS detector at the Large Hadron Collider. This search uses three production models: non-resonant and resonant Higgs boson pair production and resonant production of a pair of heavy scalar particles. Three final states, classified by the number of leptons, are analysed: two same-sign leptons, three leptons, and four leptons. No significant excess over the expected Standard Model backgrounds is observed. An observed (expected) 95% confidence-level upper limit of 160 (120) times the Standard Model prediction of non-resonant Higgs boson pair production cross-section is set from a combined analysis of the three final states. Upper limits are set on the production cross-section times branching ratio of a heavy scalar X decaying into a Higgs boson pair in the mass range of 260 GeV ≤ mχ ≤ 500 GeV and the observed (expected) limits range from 9.3 (10) pb to 2.8 (2.6) pb. Upper limits are set on the production cross-section times branching ratio of a heavy scalar Χ decaying into a pair of heavy scalars S for mass ranges of 280 GeV ≤ mχ ≤ 340 GeV and 135 GeV ≤ m_{S} ≤ 165 GeV and the observed (expected) limits range from 2.5 (2.5) pb to 0.16 (0.17) pb. © 2019, The Author(s).
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    Search for Long-Lived Neutral Particles in pp Collisions at √s=13 TeV That Decay into Displaced Hadronic Jets in the ATLAS Calorimeter
    (Springer New York Llc, 2019-06-07) Aaboud, M.; Aad, G.; Abbott, B.; Abbott, D. C.; Abdinov, O.; Abhayasinghe, D. K.; Abidi, S. H.; Izen, Joseph M.; Meirose, Bernhard; Reeves, Kendall; ATLAS Collaboration; 250674117 (Izen, JM); Izen, Joseph M.; Meirose, Bernhard; Reeves, Kendall
    This paper describes a search for pairs of neutral, long-lived particles decaying in the ATLAS calorimeter. Long-lived particles occur in many extensions to the Standard Model and may elude searches for new promptly decaying particles. The analysis considers neutral, long-lived scalars with masses between 5 and 400 GeV, produced from decays of heavy bosons with masses between 125 and 1000 GeV, where the long-lived scalars decay into Standard Model fermions. The analysis uses either 10.8 fb⁻¹ or 33.0 fb⁻¹ of data (depending on the trigger) recorded in 2016 at the LHC with the ATLAS detector in proton–proton collisions at a centre-of-mass energy of 13 TeV. No significant excess is observed, and limits are reported on the production cross section times branching ratio as a function of the proper decay length of the long-lived particles. © 2019, CERN for the benefit of the ATLAS collaboration.
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    Search for Top-Quark Decays t → Hq with 36 fb⁻¹ of pp Collision Data at √s = 13 TeV with the ATLAS Detector
    (Springer Verlag, 2019-05-21) Aaboud, M.; Aad, G.; Abbott, B.; Abbott, D. C.; Abdinov, O.; Abeloos, B.; Abhayasinghe, D. K.; Izen, Joseph M.; Meirose, Bernhard; Reeves, Kendall; ATLAS collaboration; 250674117 (Izen, JM); Izen, Joseph M.; Meirose, Bernhard; Reeves, Kendall
    A search for flavour-changing neutral current decays of a top quark into an up-type quark (q = u, c) and the Standard Model Higgs boson, t → Hq, is presented. The search is based on a dataset of pp collisions at s = 13 TeV recorded in 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider and corresponding to an integrated luminosity of 36.1 fb⁻¹. Two complementary analyses are performed to search for top-quark pair events in which one top quark decays into Wb and the other top quark decays into Hq, and target the H→ bb̅ and H → τ⁺τ⁻ decay modes, respectively. The high multiplicity of b-quark jets, or the presence of hadronically decaying τ-leptons, is exploited in the two analyses respectively. Multivariate techniques are used to separate the signal from the background, which is dominated by top-quark pair production. No significant excess of events above the background expectation is found, and 95% CL upper limits on the t → Hq branching ratios are derived. The combination of these searches with ATLAS searches in diphoton and multilepton final states yields observed (expected) 95% CL upper limits on the t → Hc and t → Hu branching ratios of 1.1 × 10⁻³ (8.3 × 10⁻⁴) and 1.2 × 10⁻³ (8.3 × 10⁻⁴), respectively. The corresponding combined observed (expected) upper limits on the |λ_{tcH}| and |λ_{tuH}| couplings are 0.064 (0.055) and 0.066 (0.055), respectively. ©2019, The Author(s).
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    Search for Low-Mass Resonances Decaying into Two Jets and Produced in Association with a Photon Using pp Collisions at √s = 13 TeV with the ATLAS Detector
    (Elsevier B.V., 2019-05-30) Aaboud, M.; Aad, G.; Abbott, B.; Abbott, D. C.; Abdinov, O.; Abed Abud, A.; Abhayasinghe, D. K.; Izen, Joseph M.; Meirose, Bernhard; Reeves, Kendall; ATLAS Collaboration; 250674117 (Izen, JM); Izen, Joseph M.; Meirose, Bernhard; Reeves, Kendall
    A search is performed for localised excesses in dijet mass distributions of low-dijet-mass events produced in association with a high transverse energy photon. The search uses up to 79.8 fb−1 of LHC proton–proton collisions collected by the ATLAS experiment at a centre-of-mass energy of 13 TeV during 2015–2017. Two variants are presented: one which makes no jet flavour requirements and one which requires both jets to be tagged as b-jets. The observed mass distributions are consistent with multi-jet processes in the Standard Model. The data are used to set upper limits on the production cross-section for a benchmark Z′ model and, separately, on generic Gaussian-shape contributions to the mass distributions, extending the current ATLAS constraints on dijet resonances to the mass range between 225 and 1100 GeV. © 2019 The Author
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    Measurement of VH, H → bb̅ Production as a Function of the Vector-Boson Transverse Momentum in 13 TeV pp Collisions with the ATLAS Detector
    (Springer Verlag, 2019-05-23) Aaboud, M.; Aad, G.; Abbott, B.; Abbott, D. C.; Abdinov, O.; Abed Abud, A.; Abhayasinghe, D. K.; ATLAS collaboration; Izen, Joseph M.; Meirose, Bernhard; Reeves, Kendall; 250674117 (Izen, JM); Izen, Joseph M.; Meirose, Bernhard; Reeves, Kendall
    Cross-sections of associated production of a Higgs boson decaying into bottomquark pairs and an electroweak gauge boson, W or Z, decaying into leptons are measured as a function of the gauge boson transverse momentum. The measurements are performed in kinematic fiducial volumes defined in the ‘simplified template cross-section’ framework. The results are obtained using 79.8 fb⁻¹ of proton-proton collisions recorded by the ATLAS detector at the Large Hadron Collider at a centre-of-mass energy of 13 TeV. All measurements are found to be in agreement with the Standard Model predictions, and limits are set on the parameters of an effective Lagrangian sensitive to modifications of the Higgs boson couplings to the electroweak gauge bosons. ©2019, The Author(s).
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    Combinations of Single-Top-Quark Production Cross-Section Measurements and |fLvV_{tb}| Determinations at √s = 7 and 8 TeV with the ATLAS and CMS Experiments
    (Springer Verlag, 2019-05-16) Aaboud, M.; Aad, G.; Abbott, B.; Abbott, D. C.; Abdinov, O.; Abed Abud, A.; Abhayasinghe, D. K.; Izen, Joseph M.; Meirose, Bernhard; Reeves, Kendall; ATLAS Collaboration; CMS Collaboration; 250674117 (Izen, JM); Izen, Joseph M.; Meirose, Bernhard; Reeves, Kendall
    This paper presents the combinations of single-top-quark production cross-section 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: t-channel, 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 s-channel cross-section, the combination yields 4.9 ± 1.4 pb at √s = 8 TeV. The square of the magnitude of the CKM matrix element V_{tb} 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 |V_{td}|, |V_{ts}| ≪ |V_{tb}|. All the |fLVV_{tb}|² determinations, extracted from individual ratios at √s = 7 and 8 TeV, are combined, resulting in |fLVV_{tb}| = 1.02 ± 0.04 (meas.) ± 0.02 (theo.). All combined measurements are consistent with their corresponding Standard Model predictions. © 2019, The Author(s).
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    Search for Electroweak Production of Supersymmetric Particles in Final States with Two or Three Leptons at √s = 13 TeV with the ATLAS Detector
    (Springer New York Llc, 2018-12-05) Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.; Abeloos, B.; Abidi, S. H.; Abouzeid, O. S.; Izen, Joseph M.; Meirose, Bernhard; Reeves, Kendall; ATLAS Collaboration; 250674117 (Izen, JM); Izen, Joseph M.; Meirose, Bernhard; Reeves, Kendall
    A search for the electroweak production of charginos, neutralinos and sleptons decaying into final states involving two or three electrons or muons is presented. The analysis is based on 36.1 fb⁻¹ of √s = 13 TeV proton– proton collisions recorded by the ATLAS detector at the Large Hadron Collider. Several scenarios based on simplified models are considered. These include the associated production of the next-to-lightest neutralino and the lightest chargino, followed by their decays into final states with leptons and the lightest neutralino via either sleptons or Standard Model gauge bosons; direct production of chargino pairs, which in turn decay into leptons and the lightest neutralino via intermediate sleptons; and slepton pair production, where each slepton decays directly into the lightest neutralino and a lepton. No significant deviations from the Standard Model expectation are observed and stringent limits at 95% confidence level are placed on the masses of relevant supersymmetric particles in each of these scenarios. For a massless lightest neutralino, masses up to 580 GeV are excluded for the associated production of the next-to-lightest neutralino and the lightest chargino, assuming gauge-boson mediated decays, whereas for slepton-pair production masses up to 500 GeV are excluded assuming three generations of mass-degenerate sleptons. © CERN for the benefit of the ATLAS collaboration 2018.
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    Search for Invisible Higgs Boson Decays in Vector Boson Fusion at √s = 13 TeV with the ATLAS Detector
    (Elsevier B.V., 2019-06-10) Aaboud, M.; Aad, G.; Abbott, B.; Abdinov, O.; Abeloos, B.; Abhayasinghe, D. K.; Abidi, S. H.; Izen, Joseph M.; Meirose, Bernhard; Reeves, Kendall; 250674117 (Izen, JM); Izen, Joseph M.; Meirose, Bernhard; Reeves, Kendall
    We report a search for Higgs bosons that are produced via vector boson fusion and subsequently decay into invisible particles. The experimental signature is an energetic jet pair with invariant mass of O(1)TeV and O(100)GeV missing transverse momentum. The analysis uses 36.1 fb⁻¹ of pp collision data at √s=13TeV recorded by the ATLAS detector at the LHC. In the signal region the 2252 observed events are consistent with the background estimation. Assuming a 125GeV scalar particle with Standard Model cross sections, the upper limit on the branching fraction of the Higgs boson decay into invisible particles is 0.37 at 95% confidence level where 0.28 was expected. This limit is interpreted in Higgs portal models to set bounds on the WIMP–nucleon scattering cross section. We also consider invisible decays of additional scalar bosons with masses up to 3TeV for which the upper limits on the cross section times branching fraction are in the range of 0.3–1.7pb. © 2019 The Author(s)

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