Browsing by Author "Abhayasinghe, D. K."
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Item 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, KendallThis 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).Item Electron and Photon Energy Calibration with the ATLAS Detector Using 2015-2016 LHC Proton-Proton Collision Data(Institute of Physics Publishing, 2019-03-18) Aaboud, M.; Aad, G.; Abbott, B.; Abbott, D. C.; Abdinov, O.; Abeloos, B.; Abhayasinghe, D. K.; Izen, Joseph M.; Meirose, Bernhard; Reeves, Kendall; 250674117 (Izen, JM); Izen, Joseph M.; Meirose, Bernhard; Reeves, KendallThis paper presents the electron and photon energy calibration obtained with the ATLAS detector using about 36 fb⁻¹ of LHC proton-proton collision data recorded at √s=13 TeV in 2015 and 2016. The different calibration steps applied to the data and the optimization of the reconstruction of electron and photon energies are discussed. The absolute energy scale is set using a large sample of Z boson decays into electron-positron pairs. The systematic uncertainty in the energy scale calibration varies between 0.03% to 0.2% in most of the detector acceptance for electrons with transverse momentum close to 45 GeV . For electrons with transverse momentum of 10 GeV the typical uncertainty is 0.3% to 0.8% and it varies between 0.25% and 1% for photons with transverse momentum around 60 GeV . Validations of the energy calibration with J/ψ → e⁺e⁻ decays and radiative Z boson decays are also presented. © 2019 CERN for the benefit of the ATLAS collaboration.Item 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, KendallStudies 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.Item 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, KendallHeavy-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.Item Measurement of Jet Fragmentation in Pb+Pb and pp Collisions at √{snn} =5.02 TeV with the ATLAS Detector(American Physical Society) Aaboud, M.; Aad, G.; Abbott, B.; 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, KendallThis paper presents a measurement of jet fragmentation functions in 0.49 nb⁻¹ of Pb+Pb collisions and 25 pb⁻¹ of pp collisions at √{sNN}=5.02 TeV collected in 2015 with the ATLAS detector at the LHC. These measurements provide insight into the jet quenching process in the quark-gluon plasma created in the aftermath of ultrarelativistic collisions between two nuclei. The modifications to the jet fragmentation functions are quantified by dividing the measurements in Pb+Pb collisions by baseline measurements in pp collisions. This ratio is studied as a function of the transverse momentum of the jet, the jet rapidity, and the centrality of the collision. In both collision systems, the jet fragmentation functions are measured for jets with transverse momentum between 126 and 398 GeV and with an absolute value of jet rapidity less than 2.1. An enhancement of particles carrying a small fraction of the jet momentum is observed, which increases with centrality and with increasing jet transverse momentum. Yields of particles carrying a very large fraction of the jet momentum are also observed to be enhanced. Between these two enhancements of the fragmentation functions a suppression of particles carrying an intermediate fraction of the jet momentum is observed in Pb+Pb collisions. A small dependence of the modifications on jet rapidity is observed.Item Measurement of the Four-Lepton Invariant Mass Spectrum in 13 TeV Proton-Proton Collisions with the ATLAS Detector(Springer Verlag) 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, KendallA measurement of the four-lepton invariant mass spectrum is made with the ATLAS detector, using an integrated luminosity of 36.1 fb⁻¹ of proton-proton collisions at √s = 13 TeV delivered by the Large Hadron Collider. The differential cross-section is measured for events containing two same-flavour opposite-sign lepton pairs. It exhibits a rich structure, with different mass regions dominated in the Standard Model by single Z boson production, Higgs boson production, and Z boson pair production, and non-negligible interference effects at high invariant masses. The measurement is compared with state-of-the-art Standard Model calculations, which are found to be consistent with the data. These calculations are used to interpret the data in terms of gg → ZZ → 4ℓ and Z → 4ℓ subprocesses, and to place constraints on a possible contribution from physics beyond the Standard Model. ©2019 The Author(s).Item Measurement of the Ratio of Cross Sections for Inclusive Isolated-Photon Production in pp Collisions at √s = 13 and 8 TeV with the ATLAS Detector(Springer Verlag) 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, KendallThe ratio of the cross sections for inclusive isolated-photon production in pp collisions at centre-of-mass energies of 13 and 8 TeV is measured using the ATLAS detector at the LHC. The integrated luminosities of the 13 TeV and 8 TeV datasets are 3.2 fb⁻¹ and 20.2 fb⁻¹, respectively. The ratio is measured as a function of the photon transverse energy in different regions of the photon pseudorapidity. The predictions from next-to-leading-order perturbative QCD calculations are compared with the measured ratio. The experimental systematic uncertainties as well as the uncertainties affecting the predictions are evaluated taking into account the correlations between the two centre-of-mass energies, resulting in a reduction of up to a factor of 2.5 (5) in the experimental (theoretical) systematic uncertainties. The predictions based on several parameterisations of the proton parton distribution functions agree with the data within the reduced experimental and theoretical uncertainties. In addition, this ratio to that of the fiducial cross sections for Z boson production at 13 and 8 TeV using the decay channels Z → e⁺e⁻ and Z → μ⁺μ⁻ is made and compared with the theoretical predictions. In this double ratio, a further reduction of the experimental uncertainty is obtained because the uncertainties arising from the luminosity measurement cancel out. The predictions describe the measurements of the double ratio within the theoretical and experimental uncertainties. ©2019 CERN, for the ATLAS Collaboration.Item Measurement of the Top Quark Mass in the tt̅ → Lepton + Jets Channel from √s=8 TeV ATLAS Data and Combination with Previous Results(Springer New York Llc) 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, KendallThe top quark mass is measured using a template method in the tt̅ → 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 tt̅ → 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 m_{top}=172.08 ± 0.39(stat) ± 0.82(syst) GeV. A combination with previous ATLAS m_{top} measurements gives m_{top}=172.69 ± 0.25(stat) ± 0.41(syst) GeV. ©2019 CERN for the benefit of the ATLAS collaboration.Item 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, KendallCross-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).Item Measurements of Inclusive and Differential Fiducial Cross-Sections of tt̅ Production with Additional Heavy-Flavour Jets in Proton-Proton Collisions at √s=13 TeV with the ATLAS Detector(Springer Verlag) 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, KendallThis paper presents measurements of tt¯ production in association with additional b-jets in pp collisions at the LHC at a centre-of-mass energy of 13 TeV. The data were recorded with the ATLAS detector and correspond to an integrated luminosity of 36.1 fb −1 . Fiducial cross-section measurements are performed in the dilepton and lepton-plus-jets tt¯ decay channels. Results are presented at particle level in the form of inclusive cross-sections of tt¯ final states with three and four b-jets as well as differential cross-sections as a function of global event properties and properties of b-jet pairs. The measured inclusive fiducial cross-sections generally exceed the tt¯ bb¯ predictions from various next-to-leading-order matrix element calculations matched to a parton shower but are compatible within the total uncertainties. The experimental uncertainties are smaller than the uncertainties in the predictions. Comparisons of state-of-the-art theoretical predictions with the differential measurements are shown and good agreement with data is found for most of them. ©2019 The Author(s).Item Observation of Electroweak W^{±} Z Boson Pair Production in Association with Two Jets in pp Collisions at√s=13 TeV with the ATLAS Detector(Elsevier B.V., 2019-05-13) 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, KendallAn observation of electroweak W^{±} Z production in association with two jets in proton–proton collisions is presented. The data collected by the ATLAS detector at the Large Hadron Collider in 2015 and 2016 at a centre-of-mass energy of √s=13 TeV are used, corresponding to an integrated luminosity of 36.1 fb⁻¹. Events containing three identified leptons, either electrons or muons, and two jets are selected. The electroweak production of W^{±} Z bosons in association with two jets is measured with an observed significance of 5.3 standard deviations. A fiducial cross-section for electroweak production including interference effects and for a single leptonic decay mode is measured to be σ_{WZjj-EW} = 0.57{_{-0.13} ^{+0.14}} (stat.) {_{-0.06) ^{+0.07}} (syst.) fb. Total and differential fiducial cross-sections of the sum of W^{±} Zjj electroweak and strong productions for several kinematic observables are also measured. © 2019 The Author(s)Item Properties of g → bb̅ at Small Opening Angles in pp Collisions with the ATLAS Detector at √s =13 TeV(American Physical Society) Aaboud, M.; Aad, G.; Abbott, B.; Abbott, D. C.; Abdinov, O.; Abeloos, B.; Abhayasinghe, D. K.; Izen, Joseph M.; Reeves, Kendall; ATLAS Collaboration; 250674117 (Izen, JM); Izen, Joseph M.; Reeves, KendallThe fragmentation of high-energy gluons at small opening angles is largely unconstrained by present measurements. Gluon splitting to b-quark pairs is a unique probe into the properties of gluon fragmentation because identified b-tagged jets provide a proxy for the quark daughters of the initial gluon. In this study, key differential distributions related to the g→bb̅ process are measured using 33 fb⁻¹ of √s=13 TeV pp collision data recorded by the ATLAS experiment at the LHC in 2016. Jets constructed from charged-particle tracks, clustered with the anti-k_t jet algorithm with radius parameter R=0.2, are used to probe angular scales below the R=0.4 jet radius. The observables are unfolded to particle level in order to facilitate direct comparisons with predictions from present and future simulations. Multiple significant differences are observed between the data and parton shower Monte Carlo predictions, providing input to improve these predictions of the main source of background events in analyses involving boosted Higgs bosons decaying into b-quarks. © 2019 CERN.Item 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, KendallA 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.Item Search for Flavor-Changing Neutral Currents in Top Quark Decays t → Hc and t → Hu in Multilepton Final States in Proton-Proton Collisions at √s =13 TeV with the ATLAS Detector(American Physical Society) 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, KendallFlavor-changing neutral currents are not present in the Standard Model at tree level and are suppressed in loop processes by the unitarity of the Cabibbo-Kobayashi-Maskawa matrix; the corresponding rates for top quark decay processes are experimentally unobservable. Extensions of the Standard Model can generate new flavor-changing neutral current processes, leading to signals which, if observed, would be unambiguous evidence of new interactions. A data set corresponding to an integrated luminosity of 36.1 fb⁻¹ of pp collisions at a center-of-mass energy of √s=13 TeV recorded with the ATLAS detector at the Large Hadron Collider is used to search for top quarks decaying to up or charm quarks with the emission of a Higgs boson, with subsequent Higgs boson decay to final states with at least one electron or muon. No signal is observed and limits on the branching fractions ℬ(t→Hc) < 0.16% and ℬ(t→Hu) < 0.19% at 95% confidence level are obtained (with expected limits of 0.15% in both cases). © 2018 CERN.Item Search for Flavor-Changing Neutral Currents in Top Quark Decays T → Hc and T → Hu in Multilepton Final States in Proton-Proton Collisions at √s =13 TeV with the ATLAS Detector(American Physical Society) 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, KendallFlavor-changing neutral currents are not present in the Standard Model at tree level and are suppressed in loop processes by the unitarity of the Cabibbo-Kobayashi-Maskawa matrix; the corresponding rates for top quark decay processes are experimentally unobservable. Extensions of the Standard Model can generate new flavor-changing neutral current processes, leading to signals which, if observed, would be unambiguous evidence of new interactions. A data set corresponding to an integrated luminosity of 36.1 fb⁻¹ of pp collisions at a center-of-mass energy of √s=13 TeV recorded with the ATLAS detector at the Large Hadron Collider is used to search for top quarks decaying to up or charm quarks with the emission of a Higgs boson, with subsequent Higgs boson decay to final states with at least one electron or muon. No signal is observed and limits on the branching fractions ℬ(t→Hc) < 0.16% and ℬ(t→Hu) < 0.19% at 95% confidence level are obtained (with expected limits of 0.15% in both cases). © 2018 CERN.Item Search for Four-Top-Quark Production in the Single-Lepton and Opposite-Sign Dilepton Final States in pp Collisions at √s =13 TeV with the ATLAS Detector(American Physical Society) 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, KendallA search for four-top-quark production, tt̅tt̅, is presented. It is based on proton-proton collision data with a center-of-mass energy √s=13 TeV collected by the ATLAS detector at the Large Hadron Collider during the years 2015 and 2016, corresponding to an integrated luminosity of 36.1 fb⁻¹. Data are analyzed in both the single-lepton and opposite-sign dilepton channels, characterized by the presence of one or two isolated electrons or muons with high-transverse momentum and multiple jets. A data-driven method is used to estimate the dominant background from top-quark pair production in association with jets. No significant excess above the Standard Model expectation is observed. The result is combined with the previous same-sign dilepton and multilepton searches carried out by the ATLAS Collaboration and an observed (expected) upper limit of 5.3 (2.1) times the four-top-quark Standard Model cross section is obtained at 95% confidence level. Additionally, an upper limit on the anomalous four-top-quark production cross section is set in the context of an effective field theory model. ©2019 CERN.Item 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, KendallThis 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.Item Search for Heavy Long-Lived Multicharged Particles in Proton-Proton Collisions at √s =13 TeV using the ATLAS Detector(American Physical Society) 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, KendallA search for heavy long-lived multicharged particles is performed using the ATLAS detector at the LHC. Data with an integrated luminosity of 36.1 fb⁻¹ collected in 2015 and 2016 from proton-proton collisions at √s=13 TeV are examined. Particles producing anomalously high ionization, consistent with long-lived massive particles with electric charges from |q|=2e to |q|=7e, are searched for. No events are observed, and 95% confidence level cross-section upper limits are interpreted as lower mass limits for a Drell-Yan production model. Multicharged particles with masses between 50 and 980-1220 GeV (depending on their electric charge) are excluded. ©2019 CERN, for the ATLAS CollaborationItem 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, KendallA 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.Item Search for Higgs Boson Pair Production in the bb̅ WW* Decay Mode at √s = 13 TeV with the ATLAS Detector(Springer Verlag, 2019) 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, KendallA search for Higgs boson pair production in the bb̅ WW* decay mode is performed in the bb̅ℓνqq final state 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. No evidence of events beyond the background expectation is found. Upper limits on the non-resonant pp → HH production cross section of 10 pb and on the resonant production cross section as a function of the HH invariant mass are obtained. Resonant production limits are set for scalar and spin-2 graviton hypotheses in the mass range 500 to 3000 GeV.©2019, The Author(s).