| 41. |
- Abulaiti, Yiming, et al.
(författare)
-
Search for a high-mass Higgs boson decaying to a W boson pair in pp collisions at root s=8TeV with the ATLAS detector
- 2016
-
Ingår i: Journal of High Energy Physics (JHEP). - 1126-6708 .- 1029-8479. ; :1
-
Tidskriftsartikel (refereegranskat)abstract
- A search for a high-mass Higgs boson H is performed in the H -> WW -> l nu l nu and H -> WW -> l nu qq decay channels using pp collision data corresponding to an integrated luminosity of 20.3 fb(-1) collected at root s = 8TeV by the ATLAS detector at the Large Hadron Collider. No evidence of a high-mass Higgs boson is found. Limits on sigma(H) x BR(H -> WW) as a function of the Higgs boson mass m(H) are determined in three different scenarios: one in which the heavy Higgs boson has a narrow width compared to the experimental resolution, one for a width increasing with the boson mass and modeled by the complex-pole scheme following the same behavior as in the Standard Model, and one for intermediate widths. The upper range of the search is m(H) = 1500 GeV for the narrow-width scenario and m(H) = 1000 GeV for the other two scenarios. The lower edge of the search range is 200{300 GeV and depends on the analysis channel and search scenario. For each signal interpretation, individual and combined limits from the two WW decay channels are presented. At m(H) = 1500 GeV, the highest-mass point tested, sigma(H) x BR(H -> WW) for a narrow-width Higgs boson is constrained to be less than 22 fb and 6.6 fb at 95% CL for the gluon fusion and vector-boson fusion production modes, respectively.
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| 42. |
- Abulaiti, Yiming, et al.
(författare)
-
Search for anomalous couplings in the Wtb vertex from the measurement of double differential angular decay rates of single top quarks produced in the t-channel with the ATLAS detector
- 2016
-
Ingår i: Journal of High Energy Physics (JHEP). - : Springer. - 1126-6708 .- 1029-8479. ; :4
-
Tidskriftsartikel (refereegranskat)abstract
- The electroweak production and subsequent decay of single top quarks is determined by the properties of the Wtb vertex. This vertex can be described by the complex parameters of an effective Lagrangian. An analysis of angular distributions of the decay products of single top quarks produced in the t-channel constrains these parameters simultaneously. The analysis described in this paper uses 4.6 fb(-1) of proton-proton collision data at root s = 7 TeV collected with the ATLAS detector at the LHC. Two parameters are measured simultaneously in this analysis. The fraction f(1) of decays containing transversely polarised W bosons is measured to be 0.37 +/- 0.07 (stat. circle plus syst.). The phase delta_ between amplitudes for transversely and longitudinally polarised W bosons recoiling against lefthanded b-quarks is measured to be -0.014 pi +/- 0.036 pi (stat. circle plus syst.). The correlation in the measurement of these parameters is 0.15. These values result in two-dimensional limits at the 95% confidence level on the ratio of the complex coupling parameters g(R) and V-L, yielding R-e[g(R)/V-L] is an element of [-0.36; 0.10] and Im[g(R)/V-L] is an element of [-0.17; 0.23] with a correlation of 0.11. The results are in good agreement with the predictions of the Standard Model.
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| 43. |
- Abulaiti, Yiming, et al.
(författare)
-
Search for charged Higgs bosons in the H-+/- -> tb decay channel in pp collisions at root s=8 TeV using the ATLAS detector
- 2016
-
Ingår i: Journal of High Energy Physics (JHEP). - 1126-6708 .- 1029-8479. ; :3
-
Tidskriftsartikel (refereegranskat)abstract
- Charged Higgs bosons heavier than the top quark and decaying via H-+/- -> tb are searched for in proton-proton collisions measured with the ATLAS experiment at root s = 8 TeV corresponding to an integrated luminosity of 20.3 fb(-1). The production of a charged Higgs boson in association with a top quark, gb -> tH(+/-), is explored in the mass range 200 to 600 GeV using multi-jet final states with one electron or muon. In order to separate the signal from the Standard Model background, analysis techniques combining several kinematic variables are employed. An excess of events above the background only hypothesis is observed across a wide mass range, amounting to up to 2.4 standard deviations. Upper limits are set on the gb -> tH(+/-) production cross section times the branching fraction BR(H-+/- -> tb). Additionally, the complementary s-channel production, qq' -> H-+/-, is investigated through a reinterpretation of W' -> tb searches in ATLAS. Final states with one electron or muon are relevant for H-+/- masses from 0.4 to 2.0 TeV, whereas the all-hadronic final state covers the range 1.5 to 3.0 TeV. In these search channels, no significant excesses from the predictions of the Standard Model are observed, and upper limits are placed on the qq' -> H-+/- production cross section times the branching fraction BR(H-+/- -> tb).
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| 44. |
- Abulaiti, Yiming, et al.
(författare)
-
Search for dark matter produced in association with a Higgs boson decaying to two bottom quarks in pp collisions at root s=8 TeV with the ATLAS detector
- 2016
-
Ingår i: Physical Review D. - : American Physical Society. - 2470-0010 .- 1550-7998 .- 1550-2368. ; 93:7
-
Tidskriftsartikel (refereegranskat)abstract
- This article reports on a search for dark matter pair production in association with a Higgs boson decaying to a pair of bottom quarks, using data from 20.3 fb(-1) of pp collisions at a center-of-mass energy of 8 TeV collected by the ATLAS detector at the LHC. The decay of the Higgs boson is reconstructed as a high-momentum b (b) over bar system with either a pair of small-radius jets, or a single large-radius jet with substructure. The observed data are found to be consistent with the expected Standard Model backgrounds. Model-independent upper limits are placed on the visible cross sections for events with a Higgs boson decaying into b (b) over bar and large missing transverse momentum with thresholds ranging from 150 to 400 GeV. Results are interpreted using a simplified model with a Z' gauge boson decaying into different Higgs bosons predicted in a two-Higgs-doublet model, of which the heavy pseudoscalar Higgs decays into a pair of dark matter particles. Exclusion limits are also presented for the mass scales of various effective field theory operators that describe the interaction between dark matter particles and the Higgs boson.
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| 45. |
- Abulaiti, Yiming, et al.
(författare)
-
Search for direct top squark pair production in final states with two tau leptons in pp collisions at root s=8 TeV with the ATLAS detector
- 2016
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 76:2
-
Tidskriftsartikel (refereegranskat)abstract
- A search for direct pair production of the supersymmetric partner of the top quark, decaying via a scalar tau to a nearly massless gravitino, has been performed using 20 fb(-1) of proton-proton collision data at root s = 8 TeV. The data were collected by the ATLAS experiment at the LHC in 2012. Top squark candidates are searched for in events with either two hadronically decaying tau leptons, one hadronically decaying tau and one light lepton, or two light leptons. No significant excess over the Standard Model expectation is found. Exclusion limits at 95 % confidence level are set as a function of the top squark and scalar tau masses. Depending on the scalar tau mass, ranging from the 87 GeV LEP limit to the top squark mass, lower limits between 490 and 650 GeV are placed on the top squark mass within the model considered.
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| 46. |
- Abulaiti, Yiming, et al.
(författare)
-
Search for gluinos in events with an isolated lepton, jets and missing transverse momentum at root 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
- The results of a search for gluinos in final states with an isolated electron or muon, multiple jets and large missing transverse momentum using proton-proton collision data at a centre-of-mass energy of root s = 13 TeV are presented. The dataset used was recorded in 2015 by the ATLAS experiment at the Large Hadron Collider and corresponds to an integrated luminosity of 3.2 fb(-1). Six signal selections are defined that best exploit the signal characteristics. The data agree with the Standard Model background expectation in all six signal selections, and the largest deviation is a 2.1 standard deviation excess. The results are interpreted in a simplified model where pair-produced gluinos decay via the lightest chargino to the lightest neutralino. In this model, gluinos are excluded up to masses of approximately 1.6 TeV depending on the mass spectrum of the simplified model, thus surpassing the limits of previous searches.
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| 47. |
- Abulaiti, Yiming, et al.
(författare)
-
Search for invisible decays of a Higgs boson using vector-boson fusion in pp collisions at root s=8 TeV with the ATLAS detector
- 2016
-
Ingår i: Journal of High Energy Physics (JHEP). - : Springer. - 1126-6708 .- 1029-8479. ; :1
-
Tidskriftsartikel (refereegranskat)abstract
- A search for a Higgs boson produced via vector-boson fusion and decaying into invisible particles is presented, using 20.3 fb(-1) of proton-proton collision data at a centre-of-mass energy of 8TeV recorded by the ATLAS detector at the LHC. For a Higgs boson with a mass of 125 GeV, assuming the Standard Model production cross section, an upper bound of 0.28 is set on the branching fraction of H -> invisible at 95% confidence level, where the expected upper limit is 0.31. The results are interpreted in models of Higgs-portal dark matter where the branching fraction limit is converted into upper bounds on the dark-matter-nucleon scattering cross section as a function of the dark-matter particle mass, and compared to results from the direct dark-matter detection experiments.
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| 48. |
- Abulaiti, Yiming, et al.
(författare)
-
Search for magnetic monopoles and stable particles with high electric charges in 8 TeV pp collisions with the ATLAS detector
- 2016
-
Ingår i: Physical Review D. - : American Physical Society. - 2470-0010 .- 2470-0029 .- 1550-2368. ; 93:5
-
Tidskriftsartikel (refereegranskat)abstract
- A search for highly ionizing particles produced in proton-proton collisions at 8 TeV center-of-mass energy is performed by the ATLAS Collaboration at the CERN Large Hadron Collider. The data set used corresponds to an integrated luminosity of 7.0 fb(-1). A customized trigger significantly increases the sensitivity, permitting a search for such particles with charges and energies beyond what was previously accessible. No events were found in the signal region, leading to production cross section upper limits in the mass range 200-2500 GeV for magnetic monopoles with magnetic charge in the range 0.5g(D) < vertical bar g vertical bar < 2.0g(D), where g(D) is the Dirac charge, and for stable particles with electric charge in the range 10 < vertical bar z vertical bar < 60. Model-dependent limits are presented in given pair-production scenarios, and model-independent limits are presented in fiducial regions of particle energy and pseudorapidity.
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| 49. |
- Abulaiti, Yiming, et al.
(författare)
-
Search for new phenomena in dijet mass and angular distributions from pp collisions at root s=13 TeV with the ATLAS detector
- 2016
-
Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 754, s. 302-322
-
Tidskriftsartikel (refereegranskat)abstract
- This Letter describes a model-agnostic search for pairs of jets (dijets) produced by resonant and non-resonant phenomena beyond the Standard Model in 3.6 fb(-1) of proton-proton collisions with a centre-of-mass energy of root s = 13 TeV recorded by the ATLAS detector at the Large Hadron Collider. The distribution of the invariant mass of the two leading jets is examined for local excesses above a data-derived estimate of the smoothly falling prediction of the Standard Model. The data are also compared to a Monte Carlo simulation of Standard Model angular distributions derived from the rapidity of the two jets. No evidence of anomalous phenomena is observed in the data, which are used to exclude, at 95% CL, quantum black holes with threshold masses below 8.3 TeV, 8.1 TeV, or 5.1 TeV in three different benchmark scenarios; resonance masses below 5.2 TeV for excited quarks, 2.6 TeV in a W' model, a range of masses starting from mZ' = 1.5 TeVand couplings from g(q) = 0.2 in a Z' model; and contact interactions with a compositeness scale below 12.0 TeV and 17.5 TeV respectively for destructive and constructive interference between the new interaction and QCD processes. These results significantly extend the ATLAS limits obtained from 8 TeV data. Gaussian-shaped contributions to the mass distribution are also excluded if the effective cross-section exceeds values ranging from approximately 50-300 fb for masses below 2 TeV to 2-20 fb for masses above 4 TeV. (C) 2016 CERN for the benefit of the ATLAS Collaboration. This is an open access article under the CC BY license.
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| 50. |
- Abulaiti, Yiming, et al.
(författare)
-
Search for new phenomena in events with at least three photons collected in pp collisions at root s=8 TeV with the ATLAS detector
- 2016
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 76:4
-
Tidskriftsartikel (refereegranskat)abstract
- Results of a search for new phenomena in events with at least three photons are reported. Data from proton-proton collisions at a centre-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 20.3 fb(-1), were collected with the ATLAS detector at the LHC. The observed data are well described by the Standard Model. Limits at the 95 % confidence level on new phenomena are presented based on the rate of events in an inclusive signal region and a restricted signal region targeting the rare decay Z -> 3 gamma, as well as di-photon and tri-photon resonance searches. For a Standard Model Higgs boson decaying to four photons via a pair of intermediate pseudoscalar particles ( a), limits are found to be sigma xBR( h -> aa) xBR(a -> gamma gamma) 2 < 10(-3) sigma(SM) for 10 GeV < m(a) < 62 GeV. Limits are also presented for Higgs boson-like scalars (H) for m(H) > 125 GeV, and for a Z' decaying to three photons via Z' -> a + gamma -> 3 gamma. Additionally, the observed limit on the branching ratio of the Z boson decay to three photons is found to be BR( Z -> 3 gamma) < 2.2 x 10(-6), a result five times stronger than the previous result from LEP.
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