3,789 research outputs found

    Measurement of the cross-section and charge asymmetry of WW bosons produced in proton-proton collisions at s=8\sqrt{s}=8 TeV with the ATLAS detector

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    This paper presents measurements of the W+μ+νW^+ \rightarrow \mu^+\nu and WμνW^- \rightarrow \mu^-\nu cross-sections and the associated charge asymmetry as a function of the absolute pseudorapidity of the decay muon. The data were collected in proton--proton collisions at a centre-of-mass energy of 8 TeV with the ATLAS experiment at the LHC and correspond to a total integrated luminosity of 20.2~\mbox{fb^{-1}}. The precision of the cross-section measurements varies between 0.8% to 1.5% as a function of the pseudorapidity, excluding the 1.9% uncertainty on the integrated luminosity. The charge asymmetry is measured with an uncertainty between 0.002 and 0.003. The results are compared with predictions based on next-to-next-to-leading-order calculations with various parton distribution functions and have the sensitivity to discriminate between them.Comment: 38 pages in total, author list starting page 22, 5 figures, 4 tables, submitted to EPJC. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2017-13

    Search for chargino-neutralino production with mass splittings near the electroweak scale in three-lepton final states in √s=13 TeV pp collisions with the ATLAS detector

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    A search for supersymmetry through the pair production of electroweakinos with mass splittings near the electroweak scale and decaying via on-shell W and Z bosons is presented for a three-lepton final state. The analyzed proton-proton collision data taken at a center-of-mass energy of √s=13  TeV were collected between 2015 and 2018 by the ATLAS experiment at the Large Hadron Collider, corresponding to an integrated luminosity of 139  fb−1. A search, emulating the recursive jigsaw reconstruction technique with easily reproducible laboratory-frame variables, is performed. The two excesses observed in the 2015–2016 data recursive jigsaw analysis in the low-mass three-lepton phase space are reproduced. Results with the full data set are in agreement with the Standard Model expectations. They are interpreted to set exclusion limits at the 95% confidence level on simplified models of chargino-neutralino pair production for masses up to 345 GeV

    Search for new phenomena in final states with an energetic jet and large missing transverse momentum in pp collisions at √ s = 8 TeV with the ATLAS detector

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    Results of a search for new phenomena in final states with an energetic jet and large missing transverse momentum are reported. The search uses 20.3 fb−1 of √ s = 8 TeV data collected in 2012 with the ATLAS detector at the LHC. Events are required to have at least one jet with pT > 120 GeV and no leptons. Nine signal regions are considered with increasing missing transverse momentum requirements between Emiss T > 150 GeV and Emiss T > 700 GeV. Good agreement is observed between the number of events in data and Standard Model expectations. The results are translated into exclusion limits on models with either large extra spatial dimensions, pair production of weakly interacting dark matter candidates, or production of very light gravitinos in a gauge-mediated supersymmetric model. In addition, limits on the production of an invisibly decaying Higgs-like boson leading to similar topologies in the final state are presente

    Dynamic biospeckle analysis, a new tool for the fast screening of plant nematicide selectivity

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    Background: Plant feeding, free-living nematodes cause extensive damage to plant roots by direct feeding and, in the case of some trichodorid and longidorid species, through the transmission of viruses. Developing more environmentally friendly, target-specific nematicides is currently impeded by slow and laborious methods of toxicity testing. Here, we developed a bioactivity assay based on the dynamics of light 'speckle' generated by living cells and we demonstrate its application by assessing chemicals' toxicity to different nematode trophic groups.Results: Free-living nematode populations extracted from soil were exposed to methanol and phenyl isothiocyanate (PEITC). Biospeckle analysis revealed differing behavioural responses as a function of nematode feeding groups. Trichodorus nematodes were less sensitive than were bacterial feeding nematodes or non-trichodorid plant feeding nematodes. Following 24 h of exposure to PEITC, bioactivity significantly decreased for plant and bacterial feeders but not for Trichodorus nematodes. Decreases in movement for plant and bacterial feeders in the presence of PEITC also led to measurable changes to the morphology of biospeckle patterns.Conclusions: Biospeckle analysis can be used to accelerate the screening of nematode bioactivity, thereby providing a fast way of testing the specificity of potential nematicidal compounds. With nematodes' distinctive movement and activity levels being visible in the biospeckle pattern, the technique has potential to screen the behavioural responses of diverse trophic nematode communities. The method discriminates both behavioural responses, morphological traits and activity levels and hence could be used to assess the specificity of nematicidal compounds.</p

    Dealing with disaffection: The influence of work-based learning on 14–16-year-old students’ attitudes to school

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    Abstract Background: Recent developments in policy concerned with raising achievement in schools have given rise to work-based learning as a mechanism for dealing with disaffection. Alongside this redress is the potential for promoting alternative pathways into further education and/or employment. This paper looks at the impact of a work-based learning programme on engagement/re-engagement for disaffected 14–16-year-olds. Drawing on data collected in a small borough in the north of England, it examines attitudes to learning in school and a vocational learning environment. Methods: Teachers’ and tutors’ attitudinal scoring of disaffected students was collected in school and a work-based learning provider, and interviews were conducted with a smaller sample of the students. Results: The retention of a strong school connection is identified as crucial in improving attitude to learning in disaffected students, while attitude and engagement is shown to be heavily interrelated. Students who solely attend a work-based learning provider are seen to further dissociate from school. Conclusions: This study explores the relationship between engagement and attitude to learning in disaffected 14-16-year-olds. Vocational learning is seen to be highly engaging and promotes an overall improvement in general attitude to learning. In relation to school, however, there is strong evidence of reinforced negative attitudes and further disaffection when students are fully removed from this environment. Thus, the most potent recipe for dealing with disaffection in this research is shown to be a mixture of environments where a connection with school is retained

    Correlated long-range mixed-harmonic fluctuations measured in pp, p+Pb and low-multiplicity Pb+Pb collisions with the ATLAS detector

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    For abstract see published article

    Search for Higgs boson decays into a pair of light bosons in the bbμμ final state in pp collision at √s=13 TeV with the ATLAS detector

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    A search for decays of the Higgs boson into a pair of new spin-zero particles, H→aa, where the a-bosons decay into a b-quark pair and a muon pair, is presented. The search uses 36.1fb−1of proton–proton collision data at √s=13 TeV recorded by the ATLAS experiment at the LHC in 2015 and 2016. No significant deviation from the Standard Model prediction is observed. Upper limits at 95% confidence level are placed on the branching ratio (σH/σSM) ×B(H→aa →bbμμ), ranging from 1.2 ×10−4to 8.4 ×10−4in the a-boson mass range of 20–60GeV. Model-independent limits are set on the visible production cross-section times the branching ratio to the bbμμ final state for new physics, σvis(X) ×B(X→bbμμ), ranging from 0.1fb to 0.73fb for mμμ between 18 and 62GeV

    Search for supersymmetry in final states with charm jets and missing transverse momentum in 13 TeV pp collisions with the ATLAS detector

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    A search for supersymmetric partners of top quarks decaying as t ~ 1 →cχ ~ 0 1 and supersymmetric partners of charm quarks decaying as c ~ 1 →cχ ~ 0 1, where χ ~ 0 1 is the lightest neutralino, is presented. The search uses 36.1 fb −1 pp collision data at a centre-of-mass energy of 13 TeV collected by the ATLAS experiment at the Large Hadron Collider and is performed in final states with jets identified as containing charm hadrons. Assuming a 100% branching ratio to cχ ~ 0 1, top and charm squarks with masses up to 850 GeV are excluded at 95% confidence level for a massless lightest neutralino. For m t ~ 1 ,c ~ 1 −m χ ~ 0 1 < 100 GeV, top and charm squark masses up to 500 GeV are excluded

    Measurement of the Higgs boson mass in the H→ZZ ∗ →4ℓ and H→γγ channels with √s =13 TeV pp collisions using the ATLAS detector

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    The mass of the Higgs boson is measured in the H→ZZ ∗ →4ℓ and in the H→γγ decay channels with 36.1 fb −1 of proton-proton collision data from the Large Hadron Collider at a centre-of-mass energy of 13 TeV recorded by the ATLAS detector in 2015 and 2016. The measured value in the H→ZZ ∗ →4ℓ channel is m ZZ ∗ H =124.79±0.37 GeV, while the measured value in the H→γγ channel is m γγ H =124.93±0.40 GeV. Combining these results with the ATLAS measurement based on 7 TeV and 8 TeV proton-proton collision data yields a Higgs boson mass of m H =124.97±0.24 GeV

    Search for B −L R-parity-violating top squarks in √s=13 TeV pp collisions with the ATLAS experiment

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    A search is presented for the direct pair production of the stop, the supersymmetric partner of the top quark, that decays through an R-parity-violating coupling to a final state with two leptons and two jets, at least one of which is identified as a b-jet. The data set corresponds to an integrated luminosity of 36.1 fb−1 of proton-proton collisions at a center-of-mass energy of √s=13 TeV, collected in 2015 and 2016 by the ATLAS detector at the LHC. No significant excess is observed over the Standard Model background, and exclusion limits are set on stop pair production at a 95% confidence level. Lower limits on the stop mass are set between 600 GeV and 1.5 TeV for branching ratios above 10% for decays to an electron or muon and a b-quark
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