35 research outputs found

    Search for flavour-changing neutral currents in processes with one top quark and a photon using 81 fb⁻¹ of pp collisions at \sqrts = 13 TeV with the ATLAS experiment

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    A search for flavour-changing neutral current (FCNC) events via the coupling of a top quark, a photon, and an up or charm quark is presented using 81 fb−1 of proton–proton collision data taken at a centre-of-mass energy of 13 TeV with the ATLAS detector at the LHC. Events with a photon, an electron or muon, a b-tagged jet, and missing transverse momentum are selected. A neural network based on kinematic variables differentiates between events from signal and background processes. The data are consistent with the background-only hypothesis, and limits are set on the strength of the tqγ coupling in an effective field theory. These are also interpreted as 95% CL upper limits on the cross section for FCNC tγ production via a left-handed (right-handed) tuγ coupling of 36 fb (78 fb) and on the branching ratio for t→γu of 2.8×10−5 (6.1×10−5). In addition, they are interpreted as 95% CL upper limits on the cross section for FCNC tγ production via a left-handed (right-handed) tcγ coupling of 40 fb (33 fb) and on the branching ratio for t→γc of 22×10−5 (18×10−5). © 2019 The Author(s

    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

    Measurement of the top-quark mass using a leptonic invariant mass in pp collisions at s√ = 13 TeV with the ATLAS detector

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    A measurement of the top-quark mass (mt) in the tt¯ → lepton + jets channel is presented, with an experimental technique which exploits semileptonic decays of b-hadrons produced in the top-quark decay chain. The distribution of the invariant mass mℓμ of the lepton, ℓ (with ℓ = e, μ), from the W-boson decay and the muon, μ, originating from the b-hadron decay is reconstructed, and a binned-template profile likelihood fit is performed to extract mt. The measurement is based on data corresponding to an integrated luminosity of 36.1 fb−1 of s√ = 13 TeV pp collisions provided by the Large Hadron Collider and recorded by the ATLAS detector. The measured value of the top-quark mass is mt = 174.41 ± 0.39 (stat.) ± 0.66 (syst.) ± 0.25 (recoil) GeV, where the third uncertainty arises from changing the PYTHIA8 parton shower gluon-recoil scheme, used in top-quark decays, to a recently developed setup

    Partição de recursos florais de espécies de Sida Linnaeus e Malvastrum coromandelianum (Linnaeus) Garcke (Malvaceae) entre Cephalurgus anomalus Moure & Oliveira (Hymenoptera, Andrenidae, Panurginae) e Melissoptila cnecomala (Moure) (Hymenoptera, Apidae, Eucerini) Floral resource partitioning on Sida Linnaeus and Malvastrum coromandelianum (Linnaeus) Garcke (Malvaceae) between Cephalurgus anomalus Moure & Oliveira (Hymenoptera, Andrenidae, Panurginae) and Melissoptila cnecomala (Moure) (Hymenoptera, Apidae, Eucerini)

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    <abstract language="eng">The flowering pattern and the visiting bee species on Sida spp. and Malvastrum coromandelianum (L.) Garcke were studied in a restricted area at the campus of the Universidade Federal de Viçosa, Minas Gerais, Brazil. There were differences among plant species but not among individuals in relation to the flowering time along the day and the time at which the flowers were visited by bees. Melissoptila cnecomala (Moure, 1944) and Cephalurgus anomalus Moure & Oliveira, 1962 were the most frequent visitors. Both species foraged on flowers for nectar and pollen. C. anomalus visited mainly plants with anthesis in the morning and M. cnecomala plants with anthesis in the afternoon. This fact sugests that those species of bees may be showing contrasting foraging strategies and can share the floral resources of Sida and Malvastrum. The males of C. anomalus mate on flowers of Sida and exhibit a behavior known as rendevouz pollination
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