2,865 research outputs found

    Estimación de Cosecha de Maíz Forrajero (Zea mays L.) Mediante Índices Espectrales Derivados de LANDSAT-8 y SENTINEL-2

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    La estimación de cosecha basada en índices espectrales conforma un elemento de decisión importante para quienes participan en la actividad agrícola; sin embargo, muchas interrogantes sobre su utilidad aún persisten. Los objetivos de esta investigación fueron: 1) relacionar propiedades radiativas del maíz forrajero (MF) y producción de biomasa mediante imágenes LANDSAT-8 y SENTINEL-2; y 2) seleccionar el índice de vegetación (IV) con mejor desempeño que permita modelar el rendimiento del MF para condiciones similares. El estudio se realizó en el ciclo PV-2019 con mediciones morfológicas en distintas etapas de crecimiento del MF y mediante muestreos aleatorios destructivos a los 72 dds para determinar magnitud de biomasa en laboratorio; los datos de biomasa se relacionaron con valores de reflectancia e IV de LANDAT-8 y SENTINEL-2 para estimar rendimiento mediante regresión lineal múltiple; ocho IV (NDVI, TVI TTVI, RDVI, RVI, RATIO, SAVI, MSAVI2) se evaluaron mediante evaluaciones cruzadas con base en estadísticos clave. Los resultados del análisis de regresión múltiple indicaron que el mejor modelo (R2 = 0.66) se obtuvo con datos de imágenes SENTINEL-2 a partir de las bandas 3 (α3 = 0.54-0.57 µm) y 8 (α8= 0.78-0.90 µm) con estimadores βi muy significativos (P < 0.05); RDVI presentó el mejor desempeño debido a una buena relación espacial entre los valores digitales ráster y la producción de biomasa verde producida con una asociación del 75.41%; en tanto que los indicadores estadísticos fueron R2= 0.75 y CME=17; con ambos recursos (Modelos de Regresión Múltiple e IV) se pronosticó el rendimiento a los 72 dds en un rango de 10.7 – 57.01 Mg ha-1. La conclusión es que SENTINEL-2 superó a LANDSAT-8 como herramienta libre para la evaluación de cultivos y estimación de biomasa debido a una mejor resolución espacial y temporal

    Constraints on the χ_(c1) versus χ_(c2) polarizations in proton-proton collisions at √s = 8 TeV

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    The polarizations of promptly produced χ_(c1) and χ_(c2) mesons are studied using data collected by the CMS experiment at the LHC, in proton-proton collisions at √s=8  TeV. The χ_c states are reconstructed via their radiative decays χ_c → J/ψγ, with the photons being measured through conversions to e⁺e⁻, which allows the two states to be well resolved. The polarizations are measured in the helicity frame, through the analysis of the χ_(c2) to χ_(c1) yield ratio as a function of the polar or azimuthal angle of the positive muon emitted in the J/ψ → μ⁺μ⁻ decay, in three bins of J/ψ transverse momentum. While no differences are seen between the two states in terms of azimuthal decay angle distributions, they are observed to have significantly different polar anisotropies. The measurement favors a scenario where at least one of the two states is strongly polarized along the helicity quantization axis, in agreement with nonrelativistic quantum chromodynamics predictions. This is the first measurement of significantly polarized quarkonia produced at high transverse momentum

    Measurement of the Y(1S) pair production cross section and search for resonances decaying to Y(1S)μ⁺μ⁻ in proton-proton collisions at √s = 13 TeV

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    The fiducial cross section for Y(1S) pair production in proton-proton collisions at a center-of-mass energy of 13 TeV in the region where both Y(1S) mesons have an absolute rapidity below 2.0 is measured to be 79±11(stat)±6(syst)±3(B) pb assuming the mesons are produced unpolarized. The last uncertainty corresponds to the uncertainty in the Y(1S) meson dimuon branching fraction. The measurement is performed in the final state with four muons using proton-proton collision data collected in 2016 by the CMS experiment at the LHC, corresponding to an integrated luminosity of 35.9fb⁻¹. This process serves as a standard model reference in a search for narrow resonances decaying to Y(1S)μ⁺μ⁻ in the same final state. Such a resonance could indicate the existence of a tetraquark that is a bound state of two b quarks and two b antiquarks. The tetraquark search is performed for masses in the vicinity of four times the bottom quark mass, between 17.5 and 19.5 GeV, while a generic search for other resonances is performed for masses between 16.5 and 27 GeV. No significant excess of events compatible with a narrow resonance is observed in the data. Limits on the production cross section times branching fraction to four muons via an intermediate Y(1S) resonance are set as a function of the resonance mass

    Search for low-mass dilepton resonances in Higgs boson decays to four-lepton final states in proton–proton collisions at √s=13TeV

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    A search for low-mass dilepton resonances in Higgs boson decays is conducted in the four-lepton final state. The decay is assumed to proceed via a pair of beyond the standard model particles, or one such particle and a Z boson. The search uses proton–proton collision data collected with the CMS detector at the CERN LHC, corresponding to an integrated luminosity of 137 fb−1, at a center-of-mass energy √s = 13 TeV. No significant deviation from the standard model expectation is observed. Upper limits at 95% confidence level are set on model-independent Higgs boson decay branching fractions. Additionally, limits on dark photon and axion-like particle production, based on two specific models, are reported

    A measurement of the Higgs boson mass in the diphoton decay channel

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    A measurement of the mass of the Higgs boson in the diphoton decay channel is presented. This analysis is based on 35.9 fb(-1) of proton-proton collision data collected during the 2016 LHC running period, with the CMS detector at a centre-of-mass energy of 13 TeV. A refined detector calibration and new analysis techniques have been used to improve the precision of this measurement. The Higgs boson mass is measured to be m(H) = 125.78 +/- 0.26GeV. This is combined with a measurement of m(H) already performed in the H -> ZZ -> 4l decay channel using the same data set, giving m(H) = 125.46 +/- 0.16GeV. This result, when further combined with an earlier measurement of m(H) using data collected in 2011 and 2012 with the CMS detector, gives a value for the Higgs boson mass of m(H) = 125.38 +/- 0.14GeV. This is currently the most precise measurement of the mass of the Higgs boson. (C) 2020 The Author(s). Published by Elsevier B.V.Peer reviewe

    Measurement of the Y(1S) pair production cross section and search for resonances decaying to Y(1S)mu(+)mu(-) in proton-proton collisions at root s=13 TeV

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    The fiducial cross section for Y(1S) pair production in proton-proton collisions at a center-of-mass energy of 13TeVin the region where both Y(1S) mesons have an absolute rapidity below 2.0 is measured to be 79 +/- 11 (stat) +/- 6 (syst) +/- 3 (B) pbassuming the mesons are produced unpolarized. The last uncertainty corresponds to the uncertainty in the Y(1S) meson dimuon branching fraction. The measurement is performed in the final state with four muons using proton-proton collision data collected in 2016 by the CMS experiment at the LHC, corresponding to an integrated luminosity of 35.9 fb(-1). This process serves as a standard model reference in a search for narrow resonances decaying to Y(1S)mu(+)mu(-) in the same final state. Such a resonance could indicate the existence of a tetraquark that is a bound state of two bquarks and two (b) over bar antiquarks. The tetraquark search is performed for masses in the vicinity of four times the bottom quark mass, between 17.5 and 19.5 GeV, while a generic search for other resonances is performed for masses between 16.5 and 27 GeV. No significant excess of events compatible with a narrow resonance is observed in the data. Limits on the production cross section times branching fraction to four muons via an intermediate Y(1S) resonance are set as a function of the resonance mass. (C) 2020 The Author(s). Published by Elsevier B.V.Peer reviewe

    The production of isolated photons in PbPb and pp collisions at sNN \sqrt{s_{\mathrm{NN}}} = 5.02 TeV

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    The transverse energy (ETγ_{T}^{γ}) spectra of photons isolated from other particles are measured using proton-proton (pp) and lead-lead (PbPb) collisions at the LHC at sNN \sqrt{s_{\mathrm{NN}}} = 5.02 TeV TeV with integrated luminosities of 27.4 pb1^{-1} and 404 μb1^{-1} for pp and PbPb data, respectively. The results are presented for photons with 25 <ETγ_{T}^{γ}< 200 GeV in the pseudorapidity range |η| < 1.44, and for different centrality intervals for PbPb collisions. Photon production in PbPb collisions is consistent with that in pp collisions scaled by the number of binary nucleon-nucleon collisions, demonstrating that photons do not interact with the quark-gluon plasma. Therefore, isolated photons can provide information about the initial energy of the associated parton in photon+jet measurements. The results are compared with predictions from the next-to-leading-order jetphox generator for different parton distribution functions (PDFs) and nuclear PDFs (nPDFs). The comparisons can help to constrain the nPDFs global fits

    Combined searches for the production of supersymmetric top quark partners in proton–proton collisions at √s=13Te

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    A combination of searches for top squark pair production using proton–proton collision data at a center-of-mass energy of 13TeV at the CERN LHC, corresponding to an integrated luminosity of 137fb1^{-1} collected by the CMS experiment, is presented. Signatures with at least 2 jets and large missing transverse momentum are categorized into events with 0, 1, or 2 leptons. New results for regions of parameter space where the kinematical properties of top squark pair production and top quark pair production are very similar are presented. Depending on the model, the combined result excludes a top squark mass up to 1325GeV for a massless neutralino, and a neutralino mass up to 700GeV for a top squark mass of 1150GeV. Top squarks with masses from 145 to 295GeV, for neutralino masses from 0 to 100GeV, with a mass difference between the top squark and the neutralino in a window of 30GeV around the mass of the top quark, are excluded for the first time with CMS data. The results of theses searches are also interpreted in an alternative signal model of dark matter production via a spin-0 mediator in association with a top quark pair. Upper limits are set on the cross section for mediator particle masses of up to 420GeV
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