| 641. |
- Milstead, David A., et al.
(författare)
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Search for lepton-flavor-violating decays of the Z boson into a τ lepton and a light lepton with the ATLAS detector
- 2018
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Ingår i: Physical Review D. - : AMER PHYSICAL SOC. - 2470-0010 .- 2470-0029. ; 98:9
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Tidskriftsartikel (refereegranskat)abstract
- Direct searches for lepton flavor violation in decays of the Z boson with the ATLAS detector at the LHC are presented. Decays of the Z boson into an electron or muon and a hadronically decaying τ lepton are considered. The searches are based on a data sample of proton-proton collisions collected by the ATLAS detector in 2015 and 2016, corresponding to an integrated luminosity of 36.1 fb-1 at a center-of-mass energy of s=13 TeV. No statistically significant excess of events above the expected background is observed, and upper limits on the branching ratios of lepton-flavor-violating decays are set at the 95% confidence level: B(Z→eτ)
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| 642. |
- Milstead, David A., et al.
(författare)
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Search for lepton-flavor violation in different-flavor, high-mass final states in pp collisions at s =13 TeV with the ATLAS detector
- 2018
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Ingår i: Physical Review D. - : AMER PHYSICAL SOC. - 2470-0010 .- 2470-0029. ; 98:9
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Tidskriftsartikel (refereegranskat)abstract
- A search is performed for a heavy particle decaying into different-flavor, dilepton pairs (eμ, eτ or μτ), using 36.1 fb-1 of proton-proton collision data at s=13 TeV collected in 2015-2016 by the ATLAS detector at the Large Hadron Collider. No excesses over the Standard Model predictions are observed. Bayesian lower limits at the 95% credibility level are placed on the mass of a Z′ boson, the mass of a supersymmetric τ-sneutrino, and on the threshold mass for quantum black-hole production. For the Z′ and sneutrino models, upper cross-section limits are converted to upper limits on couplings, which are compared with similar limits from low-energy experiments and which are more stringent for the eτ and μτ modes. © 2018 CERN, for the ATLAS Collaboration.
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| 643. |
- Milstead, David A., et al.
(författare)
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Search for long-lived neutral particles in pp collisions at √s=13TeV that decay into displaced hadronic jets in the ATLAS calorimeter
- 2019
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 79:6
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Tidskriftsartikel (refereegranskat)abstract
- 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 10.8fb-1 or 33.0fb-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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| 644. |
- Milstead, David A., et al.
(författare)
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Search for long-lived particles produced in pp collisions at s =13 TeV that decay into displaced hadronic jets in the ATLAS muon spectrometer
- 2019
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Ingår i: Physical Review D. - : American Physical Society. - 2470-0010 .- 2470-0029. ; 99:5
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Tidskriftsartikel (refereegranskat)abstract
- A search for the decay of neutral, weakly interacting, long-lived particles using data collected by the ATLAS detector at the LHC is presented. The analysis in this paper uses 36.1 fb-1 of proton-proton collision data at s=13 TeV recorded in 2015-2016. The search employs techniques for reconstructing vertices of long-lived particles decaying into jets in the muon spectrometer exploiting a two-vertex strategy and a novel technique that requires only one vertex in association with additional activity in the detector that improves the sensitivity for longer lifetimes. The observed numbers of events are consistent with the expected background and limits for several benchmark signals are determined. © 2019 CERN.
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| 645. |
- Milstead, David A., et al.
(författare)
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Search for Low-Mass Dijet Resonances Using Trigger-Level Jets with the ATLAS Detector in pp Collisions at s =13 TeV
- 2018
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Ingår i: Physical Review Letters. - : AMER PHYSICAL SOC. - 1079-7114 .- 0031-9007. ; 121:8
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Tidskriftsartikel (refereegranskat)abstract
- Searches for dijet resonances with sub-TeV masses using the ATLAS detector at the Large Hadron Collider can be statistically limited by the bandwidth available to inclusive single-jet triggers, whose data-collection rates at low transverse momentum are much lower than the rate from standard model multijet production. This Letter describes a new search for dijet resonances where this limitation is overcome by recording only the event information calculated by the jet trigger algorithms, thereby allowing much higher event rates with reduced storage needs. The search targets low-mass dijet resonances in the range 450-1800 GeV. The analyzed data set has an integrated luminosity of up to 29.3 fb-1 and was recorded at a center-of-mass energy of 13 TeV. No excesses are found; limits are set on Gaussian-shaped contributions to the dijet mass distribution from new particles and on a model of dark-matter particles with axial-vector couplings to quarks. © 2018 CERN, for the ATLAS Collaboration. Published by the American Physical Society under the terms of the »https://creativecommons.org/licenses/by/4.0/» Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP 3 .
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| 646. |
- Milstead, David A., et al.
(författare)
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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
- 2019
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Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 795, s. 56-75
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Tidskriftsartikel (refereegranskat)abstract
- 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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| 647. |
- Milstead, David A., et al.
(författare)
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Search for new phenomena using the invariant mass distribution of same-flavour opposite-sign dilepton pairs in events with missing transverse momentum in √s=13 Te pp collisions with the ATLAS detector
- 2018
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 78:8
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Tidskriftsartikel (refereegranskat)abstract
- A search for new phenomena in final states containing an e+e- or μ+μ- pair, jets, and large missing transverse momentum is presented. This analysis makes use of proton–proton collision data with an integrated luminosity of 36.1fb-1, collected during 2015 and 2016 at a centre-of-mass energy s=13TeV with the ATLAS detector at the Large Hadron Collider. The search targets the pair production of supersymmetric coloured particles (squarks or gluinos) and their decays into final states containing an e+e- or μ+μ- pair and the lightest neutralino (χ~10) via one of two next-to-lightest neutralino (χ~20) decay mechanisms: χ~20→Zχ~10, where the Z boson decays leptonically leading to a peak in the dilepton invariant mass distribution around the Z boson mass; and χ~20→ℓ+ℓ-χ~10 with no intermediate ℓ+ℓ- resonance, yielding a kinematic endpoint in the dilepton invariant mass spectrum. The data are found to be consistent with the Standard Model expectation. Results are interpreted using simplified models, and exclude gluinos and squarks with masses as large as 1.85 and 1.3 Te at 95% confidence level, respectively. © 2018, CERN for the benefit of the ATLAS collaboration.
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| 648. |
- Milstead, David A., et al.
(författare)
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Search for pair and single production of vectorlike quarks in final states with at least one Z boson decaying into a pair of electrons or muons in pp collision data collected with the ATLAS detector at root s=13 TeV
- 2018
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Ingår i: Physical Review D. - : AMER PHYSICAL SOC. - 2470-0010 .- 2470-0029. ; 98:11
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Tidskriftsartikel (refereegranskat)abstract
- A search for vectorlike quarks is presented, which targets their decay into a Z boson and a third-generation Standard Model quark. In the case of a vectorlike quark T (B) with charge +2/3e (-1/3e), the decay searched for is T -> Zt (B -> Zb). Data for this analysis were taken during 2015 and 2016 with the ATLAS detector at the Large Hadron Collider and correspond to an integrated luminosity of 36.1 fb(-1) of pp collisions at root s = 13 TeV. The final state used is characterized by the presence of b-tagged jets, as well as a Z boson with high transverse momentum, which is reconstructed from a pair of opposite-sign same-flavor leptons. Pair and single production of vectorlike quarks are both taken into account and are each searched for using optimized dileptonic exclusive and trileptonic inclusive event selections. In these selections, the high scalar sum of jet transverse momenta, the presence of high-transverse-momentum large-radius jets, as well as-in the case of the single-production selections-the presence of forward jets are used. No significant excess over the background-only hypothesis is found and exclusion limits at 95% confidence level allow masses of vectorlike quarks of m(T) > 1030 GeV (m(T) > 1210 GeV) and m(B) > 1010 GeV (m(B) > 1140 GeV) in the singlet (doublet) model. In the case of 100% branching ratio for T -> Zt (B -> Zb), the limits are m(T) > 1340 GeV (m(B) > 1220 GeV). Limits at 95% confidence level are also set on the coupling to Standard Model quarks for given vectorlike quark masses.
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| 649. |
- Milstead, David A., et al.
(författare)
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Search for pair production of heavy vector-like quarks decaying into high-p T W bosons and top quarks in the lepton-plus-jets final state in pp collisions at √s=13 TeV with the ATLAS detector
- 2018
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Ingår i: Journal of High Energy Physics. - : SPRINGER. - 1029-8479 .- 1126-6708. ; 2018:8
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Tidskriftsartikel (refereegranskat)abstract
- A search is presented for the pair production of heavy vector-like B quarks, primarily targeting B quark decays into a W boson and a top quark. The search is based on 36.1 fb−1 of pp collisions at s=13 TeV recorded in 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider. Data are analysed in the lepton-plus-jets final state, characterised by a high-transverse-momentum isolated electron or muon, large missing transverse momentum, and multiple jets, of which at least one is b-tagged. No significant deviation from the Standard Model expectation is observed. The 95% confidence level lower limit on the B mass is 1350 GeV assuming a 100% branching ratio to Wt. In the SU(2) singlet scenario, the lower mass limit is 1170 GeV. The 100% branching ratio limits are found to be also applicable to heavy vector-like X production, with charge +5/3, that decay into Wt. This search is also sensitive to a heavy vector-like B quark decaying into other final states (Zb and Hb) and thus mass limits on B production are set as a function of the decay branching ratios.[Figure not available: see fulltext.]. © 2018, The Author(s).
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| 650. |
- Milstead, David A., et al.
(författare)
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Search for pair production of heavy vectorlike quarks decaying into hadronic final states in pp collisions at s =13 TeV with the ATLAS detector
- 2018
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Ingår i: Physical Review D. - : AMER PHYSICAL SOC. - 2470-0010 .- 2470-0029. ; 98:9
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Tidskriftsartikel (refereegranskat)abstract
- A search is presented for the pair production of heavy vectorlike quarks, TT or BB, that decay into final states with jets and no reconstructed leptons. Jets in the final state are classified using a deep neural network as arising from hadronically decaying W/Z bosons, Higgs bosons, top quarks, or background. The analysis uses data from the ATLAS experiment corresponding to 36.1 fb-1 of proton-proton collisions with a center-of-mass energy of s=13 TeV delivered by the Large Hadron Collider in 2015 and 2016. No significant deviation from the Standard Model expectation is observed. Results are interpreted assuming the vectorlike quarks decay into a Standard Model boson and a third-generation-quark, T→Wb,Ht,Zt or B→Wt,Hb,Zb, for a variety of branching ratios. At 95% confidence level, the observed (expected) lower limit on the vectorlike B-quark mass for a weak-isospin doublet (B, Y) is 950 (890) GeV, and the lower limits on the masses for the pure decays B→Hb and T→Ht, where these results are strongest, are 1010 (970) GeV and 1010 (1010) GeV, respectively. © 2018 CERN, for the ATLAS Collaboration. Published by the American Physical Society.
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