23 research outputs found

    Search for single vector-like B quark production and decay via B → bH(b¯b) in pp collisions at √s = 13 TeV with the ATLAS detector

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    A search is presented for single production of a vector-like B quark decaying into a Standard Model b-quark and a Standard Model Higgs boson, which decays into a b¯b pair. The search is carried out in 139 fb−1 of √s = 13 TeV proton-proton collision data collected by the ATLAS detector at the LHC between 2015 and 2018. No significant deviation from the Standard Model background prediction is observed, and mass-dependent exclusion limits at the 95% confidence level are set on the resonance production cross-section in several theoretical scenarios determined by the couplings cW, cZ and cH between the B quark and the Standard Model W, Z and Higgs bosons, respectively. For a vector-like B occurring as an isospin singlet, the search excludes values of cW greater than 0.45 for a B resonance mass (mB) between 1.0 and 1.2 TeV. For 1.2 TeV < mB < 2.0 TeV, cW values larger than 0.50–0.65 are excluded. If the B occurs as part of a (B, Y) doublet, the smallest excluded cZ coupling values range between 0.3 and 0.5 across the investigated resonance mass range 1.0 TeV < mB < 2.0 TeV

    Search for light long-lived neutral particles that decay to collimated pairs of leptons or light hadrons in pp collisions at s√ = 13 TeV with the ATLAS detector

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    A search for light long-lived neutral particles with masses in the O(MeV–GeV) range is presented. The analysis targets the production of long-lived dark photons in the decay of a Higgs boson produced via gluon–gluon fusion or in association with a W boson. Events that contain displaced collimated Standard Model fermions reconstructed in the calorimeter or muon spectrometer are selected in 139 fb−1 of s√ = 13 TeV pp collision data collected by the ATLAS detector at the LHC. Background estimates for contributions from Standard Model processes and instrumental effects are extracted from data. The observed event yields are consistent with the expected background. Exclusion limits are reported on the production cross-section times branching fraction as a function of the mean proper decay length cτ of the dark photon, or as a function of the dark-photon mass and kinetic mixing parameter that quantifies the coupling between the Standard Model and potential hidden (dark) sectors. A Higgs boson branching fraction above 1% is excluded at 95% CL for a Higgs boson decaying into two dark photons for dark-photon mean proper decay lengths between 10 mm and 250 mm and dark photons with masses between 0.4 GeV and 2 GeV

    Search for resonances decaying into photon pairs in 139 fb−1 of pp collisions at √s = 13 TeV with the ATLAS detector

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    Searches for new resonances in the diphoton final state, with spin 0 as predicted by theories with an extended Higgs sector and with spin 2 using a warped extra-dimension benchmark model, are presented using 139 fb−1 of √s = 13 TeV pp collision data collected by the ATLAS experiment at the LHC. No significant deviation from the Standard Model is observed and upper limits are placed on the production cross-section times branching ratio to two photons as a function of the resonance mass

    Measurements of differential cross-sections in top-quark pair events with a high transverse momentum top quark and limits on beyond the Standard Model contributions to top-quark pair production with the ATLAS detector at s√ = 13 TeV

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    Cross-section measurements of top-quark pair production where the hadronically decaying top quark has transverse momentum greater than 355 GeV and the other top quark decays into â„“Îœb are presented using 139 fb−1 of data collected by the ATLAS experiment during proton-proton collisions at the LHC. The fiducial cross-section at s√ = 13 TeV is measured to be σ = 1.267 ± 0.005 ± 0.053 pb, where the uncertainties reflect the limited number of data events and the systematic uncertainties, giving a total uncertainty of 4.2%. The cross-section is measured differentially as a function of variables characterising the ttÂŻ system and additional radiation in the events. The results are compared with various Monte Carlo generators, including comparisons where the generators are reweighted to match a parton-level calculation at next-to-next-to-leading order. The reweighting improves the agreement between data and theory. The measured distribution of the top-quark transverse momentum is used to search for new physics in the context of the effective field theory framework. No significant deviation from the Standard Model is observed and limits are set on the Wilson coefficients of the dimension-six operators OtG and O(8)tq, where the limits on the latter are the most stringent to date

    Observation of WWWWWW Production in pppp Collisions at s\sqrt s =13  TeV with the ATLAS Detector

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    International audienceThis Letter reports the observation of WWWWWW production and a measurement of its cross section using 139 fb−1^{-1} of proton-proton collision data recorded at a center-of-mass energy of 13 TeV by the ATLAS detector at the Large Hadron Collider. Events with two same-sign leptons (electrons or muons) and at least two jets, as well as events with three charged leptons, are selected. A multivariate technique is then used to discriminate between signal and background events. Events from WWWWWW production are observed with a significance of 8.0 standard deviations, where the expectation is 5.4 standard deviations. The inclusive WWWWWW production cross section is measured to be 820±100 (stat)±80 (syst)820 \pm 100\,\text{(stat)} \pm 80\,\text{(syst)} fb, approximately 2.6 standard deviations from the predicted cross section of 511±18511 \pm 18 fb calculated at next-to-leading-order QCD and leading-order electroweak accuracy

    Observation of WWWWWW Production in pppp Collisions at s\sqrt s =13  TeV with the ATLAS Detector

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    International audienceThis Letter reports the observation of WWWWWW production and a measurement of its cross section using 139 fb−1^{-1} of proton-proton collision data recorded at a center-of-mass energy of 13 TeV by the ATLAS detector at the Large Hadron Collider. Events with two same-sign leptons (electrons or muons) and at least two jets, as well as events with three charged leptons, are selected. A multivariate technique is then used to discriminate between signal and background events. Events from WWWWWW production are observed with a significance of 8.0 standard deviations, where the expectation is 5.4 standard deviations. The inclusive WWWWWW production cross section is measured to be 820±100 (stat)±80 (syst)820 \pm 100\,\text{(stat)} \pm 80\,\text{(syst)} fb, approximately 2.6 standard deviations from the predicted cross section of 511±18511 \pm 18 fb calculated at next-to-leading-order QCD and leading-order electroweak accuracy

    Observation of WWWWWW Production in pppp Collisions at s\sqrt s =13  TeV with the ATLAS Detector

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    International audienceThis Letter reports the observation of WWWWWW production and a measurement of its cross section using 139 fb−1^{-1} of proton-proton collision data recorded at a center-of-mass energy of 13 TeV by the ATLAS detector at the Large Hadron Collider. Events with two same-sign leptons (electrons or muons) and at least two jets, as well as events with three charged leptons, are selected. A multivariate technique is then used to discriminate between signal and background events. Events from WWWWWW production are observed with a significance of 8.0 standard deviations, where the expectation is 5.4 standard deviations. The inclusive WWWWWW production cross section is measured to be 820±100 (stat)±80 (syst)820 \pm 100\,\text{(stat)} \pm 80\,\text{(syst)} fb, approximately 2.6 standard deviations from the predicted cross section of 511±18511 \pm 18 fb calculated at next-to-leading-order QCD and leading-order electroweak accuracy

    Search for new phenomena in three- or four-lepton events in pp collisions at root s=13 TeV with the ATLAS detector

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    We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. We acknowledge the support of ANPCyT, Argentina; YerPhI, Ar-menia; ARC, Australia; BMWFW and FWF, Austria; ANAS, Azerbai-jan; SSTC, Belarus; CNPq and FAPESP, Brazil; NSERC, NRC and CFI, Canada; CERN; ANID, Chile; CAS, MOST and NSFC, China; Min-ciencias, Colombia; MSMT CR, MPO CR and VSC CR, Czech Repub-lic; DNRF and DNSRC, Denmark; IN2P3-CNRS and CEA-DRF/IRFU, France; SRNSFG, Georgia; BMBF, HGF and MPG, Germany; GSRI, Greece; RGC and Hong Kong SAR, China; ISF and Benoziyo Cen-ter, Israel; INFN, Italy; MEXT and JSPS, Japan; CNRST, Morocco; NWO, Netherlands; RCN, Norway; MEiN, Poland; FCT, Portugal; MNE/IFA, Romania; JINR; MES of Russia and NRC KI, Russian Fed-eration; MESTD, Serbia; MSSR, Slovakia; ARRS and MIZĆ , Slovenia; DSI/NRF, South Africa; MICINN, Spain; SRC and Wallenberg Founda-tion, Sweden; SERI, SNSF and Cantons of Bern and Geneva, Switzer-land; MOST, Taiwan; TAEK, Turkey; STFC, United Kingdom; DOE and NSF, United States of America. In addition, individual groups and members have received support from BCKDF, CANARIE, Com-pute Canada and CRC, Canada; COST, ERC, ERDF, Horizon 2020 and Marie SkƂodowska-Curie Actions, European Union; Investisse-ments d’Avenir Labex, Investissements d’Avenir Idex and ANR, France; DFG and AvH Foundation, Germany; Herakleitos, Thales and Aristeia programmes co-financed by EU-ESF and the Greek NSRF, Greece; BSF-NSF and GIF, Israel; Norwegian Financial Mecha-nism 2014-2021, Norway; NCN and NAWA, Poland; La Caixa Bank-ing Foundation, CERCA Programme Generalitat de Catalunya and PROMETEO and GenT Programmes Generalitat Valenciana, Spain; Göran Gustafssons Stiftelse, Sweden; The Royal Society and Lever-hulme Trust, United Kingdom. The crucial computing support from all WLCG partners is ac-knowledged gratefully, in particular from CERN, the ATLAS Tier-1 facilities at TRIUMF (Canada), NDGF (Denmark, Norway, Sweden), CC-IN2P3 (France), KIT/GridKA (Germany), INFN-CNAF (Italy), NL-T1 (Netherlands), PIC (Spain), ASGC (Taiwan), RAL (UK) and BNL (USA), the Tier-2 facilities worldwide and large non-WLCG resource providers. Major contributors of computing resources are listed in Ref.[91].A search with minimal model dependence for physics beyond the Standard Model in events featuring three or four charged leptons (3l and 4l, l = e, mu) is presented. The analysis aims to be sensitive to a wide range of potential new-physics theories simultaneously. This analysis uses data from pp collisions delivered by the Large Hadron Collider at a centre-of-mass energy of root s = 13 TeV and recorded with the ATLAS detector, corresponding to the full Run 2 dataset of 139 fb(-1). The 3l and 4l phase space is divided into 22 event categories according to the number of leptons in the event, the missing transverse momentum, the invariant mass of the leptons, and the presence of leptons originating from a Z-boson candidate. These event categories are analysed independently for the presence of deviations from the Standard Model. No statistically significant deviations from the Standard Model predictions are observed. Upper limits for all signal regions are reported in terms of the visible cross-section.ANPCyT, ArgentinaYerPhI, ArmeniaARC, AustraliaBMWFW and FWF, AustriaANAS, AzerbaijanSSTC, BelarusCNPq and FAPESP, BrazilNSERC, NRC and CFI, CanadaCERNANID, ChileCAS, MOST and NSFC, ChinaMinciencias, ColombiaMSMT CR, MPO CR and VSC CR, Czech RepublicDNRF and DNSRC, DenmarkIN2P3-CNRS and CEA-DRF/IRFU, FranceSRNSFG, GeorgiaBMBF, HGF and MPG, GermanyGSRI, GreeceRGC and Hong Kong SAR, ChinaISF and Benoziyo Center, IsraelINFN, ItalyMEXT and JSPS, JapanCNRST, MoroccoNWO, NetherlandsRCN, NorwayMEiN, PolandFCT, PortugalMNE/IFA, RomaniaJINRMES of Russia and NRC KI, Russian FederationMESTD, SerbiaMSSR, SlovakiaARRS and MIZĆ , SloveniaDSI/NRF, South AfricaMICINN, SpainSRC and Wallenberg Foundation, SwedenSERI, SNSF and Cantons of Bern and Geneva, SwitzerlandMOST, TaiwanTAEK, TurkeySTFC, United KingdomDOE and NSF, United States of AmericaBCKDF, CANARIE, Compute Canada and CRC, CanadaCOST, ERC, ERDF, Horizon 2020 and Marie SkƂodowska-Curie Actions, European UnionInvestissements d’Avenir Labex, Investissements d’Avenir Idex and ANR, FranceDFG and AvH Foundation, GermanyHerakleitos, Thales and Aristeia programmes co-financed by EU-ESF and the Greek NSRF, GreeceBSF-NSF and GIF, IsraelNorwegian Financial Mechanism 2014-2021, NorwayNCN and NAWA, PolandLa Caixa Banking Foundation, CERCA Programme Generalitat de Catalunya and PROMETEO and GenT Programmes Generalitat Valenciana, SpainGöran Gustafssons Stiftelse, SwedenThe Royal Society and Leverhulme Trust, United Kingdo

    Observation of WWWWWW Production in pppp Collisions at s\sqrt s =13  TeV with the ATLAS Detector

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    International audienceThis Letter reports the observation of WWWWWW production and a measurement of its cross section using 139 fb−1^{-1} of proton-proton collision data recorded at a center-of-mass energy of 13 TeV by the ATLAS detector at the Large Hadron Collider. Events with two same-sign leptons (electrons or muons) and at least two jets, as well as events with three charged leptons, are selected. A multivariate technique is then used to discriminate between signal and background events. Events from WWWWWW production are observed with a significance of 8.0 standard deviations, where the expectation is 5.4 standard deviations. The inclusive WWWWWW production cross section is measured to be 820±100 (stat)±80 (syst)820 \pm 100\,\text{(stat)} \pm 80\,\text{(syst)} fb, approximately 2.6 standard deviations from the predicted cross section of 511±18511 \pm 18 fb calculated at next-to-leading-order QCD and leading-order electroweak accuracy

    Search for new phenomena in final states with photons, jets and missing transverse momentum in pp collisions at s \sqrt{s} = 13 TeV with the ATLAS detector

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    International audienceA search for new phenomena has been performed in final states with at least one isolated high-momentum photon, jets and missing transverse momentum in proton–proton collisions at a centre-of-mass energy of s \sqrt{s} = 13 TeV. The data, collected by the ATLAS experiment at the CERN LHC, correspond to an integrated luminosity of 139 fb−1^{−1}. The experimental results are interpreted in a supersymmetric model in which pair-produced gluinos decay into neutralinos, which in turn decay into a gravitino, at least one photon, and jets. No significant deviations from the predictions of the Standard Model are observed. Upper limits are set on the visible cross section due to physics beyond the Standard Model, and lower limits are set on the masses of the gluinos and neutralinos, all at 95% confidence level. Visible cross sections greater than 0.022 fb are excluded and pair-produced gluinos with masses up to 2200 GeV are excluded for most of the NLSP masses investigated.[graphic not available: see fulltext
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