357 research outputs found

    Roadside Car Surveys: Methodological Constraints and Solutions for Estimating Parrot Abundances across the World

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    Parrots stand out among birds because of their poor conservation status and the lack of available information on their population sizes and trends. Estimating parrot abundance is complicated by the high mobility, gregariousness, patchy distributions, and rarity of many species. Roadside car surveys can be useful to cover large areas and increase the probability of detecting spatially aggregated species or those occurring at very low densities. However, such surveys may be biased due to their inability to handle differences in detectability among species and habitats. We conducted 98 roadside surveys, covering > 57,000 km across 20 countries and the main world biomes, recording ca. 120,000 parrots from 137 species. We found that larger and more gregarious species are more easily visually detected and at greater distances, with variations among biomes. However, raw estimates of relative parrot abundances (individuals/km) were strongly correlated (r = 0.86–0.93) with parrot densities (individuals/km2) estimated through distance sampling (DS) models, showing that variability in abundances among species (>40 orders of magnitude) overcomes any potential detectability bias. While both methods provide similar results, DS cannot be used to study parrot communities or monitor the population trends of all parrot species as it requires a minimum of encounters that are not reached for most species (64% in our case), mainly the rarest and more threatened. However, DS may be the most suitable choice for some species-specific studies of common species. We summarize the strengths and weaknesses of both methods to guide researchers in choosing the best–fitting option for their particular research hypotheses, characteristics of the species studied, and logistical constraints.This research was funded by Fundación Biodiversidad (Spanish Ministerio de Medio Ambiente, project 52I.CA2109), Fundación Repsol, Spanish Ministerio de Ciencia e Innovación (Project CGL2015-71378-P), and mostly by Loro Parque Fundación (Project SEJI/2018/024).Peer reviewe

    Search for top squark pair production in pp collisions at root s=13 TeV using single lepton events

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    Observation of ttˉ\bar{t}H Production

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    The observation of Higgs boson production in association with a top quark-antiquark pair is reported, based on a combined analysis of proton-proton collision data at center-of-mass energies of s√=7, 8, and 13 TeV, corresponding to integrated luminosities of up to 5.1, 19.7, and 35.9fb−1, respectively. The data were collected with the CMS detector at the CERN LHC. The results of statistically independent searches for Higgs bosons produced in conjunction with a top quark-antiquark pair and decaying to pairs of W bosons, Z bosons, photons, τ leptons, or bottom quark jets are combined to maximize sensitivity. An excess of events is observed, with a significance of 5.2 standard deviations, over the expectation from the background-only hypothesis. The corresponding expected significance from the standard model for a Higgs boson mass of 125.09 GeV is 4.2 standard deviations. The combined best fit signal strength normalized to the standard model prediction is 1.26+0.31−0.26

    Evidence for associated production of a Higgs boson with a top quark pair in final states with electrons, muons, and hadronically decaying τ leptons at s=13 \sqrt{s}=13 TeV

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    Results of a search for the standard model Higgs boson produced in association with a top quark pair (tt¯H) in final states with electrons, muons, and hadronically decaying τ leptons are presented. The analyzed data set corresponds to an integrated luminosity of 35.9 fb−1 recorded in proton-proton collisions at s√=13 TeV by the CMS experiment in 2016. The sensitivity of the search is improved by using matrix element and machine learning methods to separate the signal from backgrounds. The measured signal rate amounts to 1.23 − 0.43 + 0.45 times the production rate expected in the standard model, with an observed (expected) significance of 3.2σ (2.8σ), which represents evidence for tt¯H production in those final states. An upper limit on the signal rate of 2.1 times the standard model production rate is set at 95% confidence level

    Measurement of differential cross sections for inclusive isolated-photon and photon+jet production in proton-proton collisions at s=13TeV\sqrt{s} = 13\,\text {TeV}

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    Measurements of inclusive isolated-photon and photon+jet production in proton–proton collisions at s √ =13TeV s=13TeV are presented. The analysis uses data collected by the CMS experiment in 2015, corresponding to an integrated luminosity of 2.26fb −1 fb−1 . The cross section for inclusive isolated photon production is measured as a function of the photon transverse energy in a fiducial region. The cross section for photon+jet production is measured as a function of the photon transverse energy in the same fiducial region with identical photon requirements and with the highest transverse momentum jet. All measurements are in agreement with predictions from next-to-leading-order perturbative QCD

    Study of the underlying event in top quark pair production in pp collisions at 13 TeV

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    Measurements of normalized differential cross sections as functions of the multiplicity and kinematic variables of charged-particle tracks from the underlying event in top quark and antiquark pair production are presented. The measurements are performed in proton-proton collisions at a center-of-mass energy of 13<, and are based on data collected by the CMS experiment at the LHC in 2016 corresponding to an integrated luminosity of 35.9fb(-1). Events containing one electron, one muon, and two jets from the hadronization and fragmentation of b quarks are used. These measurements characterize, for the first time, properties of the underlying event in top quark pair production and show no deviation from the universality hypothesis at energy scales typically above twice the top quark mass.Peer reviewe

    Measurement of exclusive rho(770)(0) photoproduction in ultraperipheral pPb collisions at root s(NN)=5.02 TeV

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    Exclusive.(770) 0 photoproduction is measured for the first time in ultraperipheral pPb collisions at v s NN = 5.02 TeV with the CMS detector. The cross section s(.p..(770) 0 p) is 11.0 +/- 1.4 (stat) +/- 1.0 (syst) mu b at W. p = 92.6GeV for photon-proton centre-of-mass energies W. p between 29 and 213 GeV. The differential cross section ds/d| t| is measured in the interval 0.025 <| t| <1GeV 2 as a function of W. p, where t is the squared four-momentum transfer at the proton vertex. The results are compared with previous measurements and theoretical predictions. The measured cross section s(.p..(770) 0 p) has a power-law dependence on the photon-proton centre-of-mass, consistent with electron-proton collision measurements performed at HERA. The W. p dependence of the exponential slope of the differential cross section ds/d| t| is also measured.Peer reviewe

    Inclusive Search for a Highly Boosted Higgs Boson Decaying to a Bottom Quark-Antiquark Pair

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    Search for t(t)over-barH production in the H -> b(b)over-bar decay channel with leptonic t(t)over-bar decays in proton-proton collisions at root s=13 TeV

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    A search has been performed for heavy resonances decaying to ZZ or ZW in 2l2q final states, with two charged leptons (l = e, mu) produced by the decay of a Z boson, and two quarks produced by the decay of a W or Z boson. The analysis is sensitive to resonances with masses in the range from 400 to 4500 GeV. Two categories are defined based on the merged or resolved reconstruction of the hadronically decaying vector boson, optimized for high- and low-mass resonances, respectively. The search is based on data collected during 2016 by the CMS experiment at the LHC in proton-proton collisions with a center-of-mass energy of root s = 13 TeV, corresponding to an integrated luminosity of 35.9 fb(-1). No excess is observed in the data above the standard model background expectation. Upper limits on the production cross section of heavy, narrow spin-1 and spin-2 resonances are derived as a function of the resonance mass, and exclusion limits on the production of W' bosons and bulk graviton particles are calculated in the framework of the heavy vector triplet model and warped extra dimensions, respectively.A search has been performed for heavy resonances decaying to ZZ or ZW in 2l2q final states, with two charged leptons (l = e, mu) produced by the decay of a Z boson, and two quarks produced by the decay of a W or Z boson. The analysis is sensitive to resonances with masses in the range from 400 to 4500 GeV. Two categories are defined based on the merged or resolved reconstruction of the hadronically decaying vector boson, optimized for high- and low-mass resonances, respectively. The search is based on data collected during 2016 by the CMS experiment at the LHC in proton-proton collisions with a center-of-mass energy of root s = 13 TeV, corresponding to an integrated luminosity of 35.9 fb(-1). No excess is observed in the data above the standard model background expectation. Upper limits on the production cross section of heavy, narrow spin-1 and spin-2 resonances are derived as a function of the resonance mass, and exclusion limits on the production of W' bosons and bulk graviton particles are calculated in the framework of the heavy vector triplet model and warped extra dimensions, respectively.A search is presented for the associated production of a standard model Higgs boson with a top quark-antiquark pair (ttH), in which the Higgs boson decays into a b quark-antiquark pair, in proton-proton collisions at a centre-of-mass energy =13 TeV. The data correspond to an integrated luminosity of 35.9 fb(-1) recorded with the CMS detector at the CERN LHC. Candidate ttH events are selected that contain either one or two electrons or muons from the t decays and are categorised according to the number of jets. Multivariate techniques are employed to further classify the events and eventually discriminate between signal and background. The results are characterised by an observed tH signal strength relative to the standard model cross section, = sigma/sigma(SM), under the assumption of a Higgs boson mass of 125 GeV. A combined fit of multivariate discriminant distributions in all categories results in an observed (expected) upper limit on of 1.5 (0.9) at 95% confidence level, and a best fit value of 0.72 +/- 0.24(stat) +/- 0.38(syst), corresponding to an observed (expected) signal significance of 1.6 (2.2) standard deviations above the background-only hypothesis.Peer reviewe
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