101 research outputs found

    Search for pair production of the scalar top quark in the electron-muon final state

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    We report the result of a search for the pair production of the lightest supersymmetric partner of the top quark (t~1\tilde{t}_1) in ppˉp\bar{p} collisions at a center-of-mass energy of 1.96 TeV at the Fermilab Tevatron collider corresponding to an integrated luminosity of 5.4 fb1^{-1}. The scalar top quarks are assumed to decay into a bb quark, a charged lepton, and a scalar neutrino (ν~\tilde{\nu}), and the search is performed in the electron plus muon final state. No significant excess of events above the standard model prediction is detected, and improved exclusion limits at the 95% C.L. are set in the the (Mt~1M_{\tilde{t}_1},Mν~M_{\tilde{\nu}}) mass plane

    A measurement of the ratio of inclusive cross sections σ(ppˉZ+bjet)/σ(ppˉZ+jet)\sigma(p\bar{p}\rightarrow Z+b{\rm\, jet})/ \sigma(p\bar{p}\rightarrow Z+{\rm jet}) at s=1.96\sqrt{s}=1.96 TeV

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    The ratio of the cross section for ppˉp\bar{p} interactions producing a ZZ boson and at least one bb quark jet to the inclusive Z+jetZ+{\rm jet} cross section is measured using 4.2 fb14.2\ {\rm fb}^{-1} of ppˉp\bar{p} collisions collected with the \dzero\ detector at the Fermilab Tevatron collider at s=1.96\sqrt{s}=1.96 TeV. The Z+Z\rightarrow\ell^+\ell^- candidate events with at least one bb jet are discriminated from Z+Z+ charm and light jet(s) events by a novel technique that exploits the properties of the tracks associated to the jet. The measured ratio is 0.0193±0.00270.0193\pm0.0027 for events having a jet with transverse momentum \pt > 20 \GeV and pseudorapidity η2.5|\eta| \leq 2.5, which is the most precise to date and is consistent with theoretical predictions.Comment: Submitted to Phys. Rev. Let

    Search for a heavy neutral gauge boson in the dielectron channel with 5.4 fb-1 of ppbar collisions at sqrt(s) = 1.96 TeV

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    We report the results of a search for a heavy neutral gauge boson Z' decaying into the dielectron final state using data corresponding to an integrated luminosity of 5.4 fb-1 collected by the D0 experiment at the Fermilab Tevatron Collider. No significant excess above the standard model prediction is observed in the dielectron invariant-mass spectrum. We set 95% C.L. upper limits on \sigma (ppbar -> Z') X BR(Z' -> ee) depending on the dielectron invariant mass. These cross section limits are used to determine lower mass limits for Z' bosons in a variety of models with standard model couplings and variable strength.Comment: 8 pages, 4 figure

    High mass exclusive diffractive dijet production in ppˉ\mathbf{p\bar{p}} collisions at s\mathbf{\sqrt{s}} = 1.96 TeV

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    We present evidence for diffractive exclusive dijet production with an invariant dijet mass greater than 100 GeV in data collected with the D0 experiment at the Fermilab Tevatron Collider. A discriminant based on calorimeter information is used to measure a significant number of events with little energy (typically less than 10 GeV) outside the dijet system, consistent with the diffractive exclusive dijet production topology. The probability for these events to be explained by other dijet production processes is 2×1052 \times 10^{-5}, corresponding to a 4.1 standard deviation significance.Comment: submitted to Phys. Lett.

    New insights into the genetic etiology of Alzheimer's disease and related dementias

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    Characterization of the genetic landscape of Alzheimer's disease (AD) and related dementias (ADD) provides a unique opportunity for a better understanding of the associated pathophysiological processes. We performed a two-stage genome-wide association study totaling 111,326 clinically diagnosed/'proxy' AD cases and 677,663 controls. We found 75 risk loci, of which 42 were new at the time of analysis. Pathway enrichment analyses confirmed the involvement of amyloid/tau pathways and highlighted microglia implication. Gene prioritization in the new loci identified 31 genes that were suggestive of new genetically associated processes, including the tumor necrosis factor alpha pathway through the linear ubiquitin chain assembly complex. We also built a new genetic risk score associated with the risk of future AD/dementia or progression from mild cognitive impairment to AD/dementia. The improvement in prediction led to a 1.6- to 1.9-fold increase in AD risk from the lowest to the highest decile, in addition to effects of age and the APOE ε4 allele

    State of the world’s plants and fungi 2020

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    Kew’s State of the World’s Plants and Fungi project provides assessments of our current knowledge of the diversity of plants and fungi on Earth, the global threats that they face, and the policies to safeguard them. Produced in conjunction with an international scientific symposium, Kew’s State of the World’s Plants and Fungi sets an important international standard from which we can annually track trends in the global status of plant and fungal diversity
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