31 research outputs found

    Measurements of the production cross-section for a Z boson in association with b- or c-jets in proton–proton collisions at √s = 13 TeV with the ATLAS detector

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    This paper presents a measurement of the production cross-section of a Z boson in association with bor c-jets, in proton–proton collisions at √s = 13 TeV with the ATLAS experiment at the Large Hadron Collider using data corresponding to an integrated luminosity of 140 fb−1. Inclusive and differential cross-sections are measured for events containing a Z boson decaying into electrons or muons and produced in association with at least one b-jet, at least one c-jet, or at least two b-jets with transverse momentum pT > 20 GeV and rapidity |y| < 2.5. Predictions from several Monte Carlo generators based on next-to-leading-order matrix elements interfaced with a parton-shower simulation, with different choices of flavour schemes for initial-state partons, are compared with the measured cross-sections. The results are also compared with novel predictions, based on infrared and collinear safe jet flavour dressing algorithms. Selected Z+ ≥ 1 c-jet observables, optimized for sensitivity to intrinsic-charm, are compared with benchmark models with different intrinsic-charm fractions

    Electron and photon energy calibration with the ATLAS detector using LHC Run 2 data

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    This paper presents the electron and photon energy calibration obtained with the ATLAS detector using 140 fb-1 of LHC proton-proton collision data recorded at √(s) = 13 TeV between 2015 and 2018. Methods for the measurement of electron and photon energies are outlined, along with the current knowledge of the passive material in front of the ATLAS electromagnetic calorimeter. The energy calibration steps are discussed in detail, with emphasis on the improvements introduced in this paper. The absolute energy scale is set using a large sample of Z-boson decays into electron-positron pairs, and its residual dependence on the electron energy is used for the first time to further constrain systematic uncertainties. The achieved calibration uncertainties are typically 0.05% for electrons from resonant Z-boson decays, 0.4% at ET ∼ 10 GeV, and 0.3% at ET ∼ 1 TeV; for photons at ET ∼ 60 GeV, they are 0.2% on average. This is more than twice as precise as the previous calibration. The new energy calibration is validated using J/ψ → ee and radiative Z-boson decays

    Performance and calibration of quark/gluon-jet taggers using 140 fb−1 of pp collisions at √s = 13 TeV with the ATLAS detector

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    The identification of jets originating from quarks and gluons, often referred to as quark/gluon tagging, plays an important role in various analyses performed at the Large Hadron Collider, as Standard Model measurements and searches for new particles decaying to quarks often rely on suppressing a large gluon-induced background. This paper describes the measurement of the efficiencies of quark/gluon taggers developed within the ATLAS Collaboration, using √s = 13 TeV proton–proton collision data with an integrated luminosity of 140 fb-1 collected by the ATLAS experiment. Two taggers with high performances in rejecting jets from gluon over jets from quarks are studied: one tagger is based on requirements on the number of inner-detector tracks associated with the jet, and the other combines several jet substructure observables using a boosted decision tree. A method is established to determine the quark/gluon fraction in data, by using quark/gluon-enriched subsamples defined by the jet pseudorapidity. Differences in tagging efficiency between data and simulation are provided for jets with transverse momentum between 500 GeV and 2 TeV and for multiple tagger working points

    The ATLAS trigger system for LHC Run 3 and trigger performance in 2022

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    The ATLAS trigger system is a crucial component of the ATLAS experiment at the LHC. It is responsible for selecting events in line with the ATLAS physics programme. This paper presents an overview of the changes to the trigger and data acquisition system during the second long shutdown of the LHC, and shows the performance of the trigger system and its components in the proton-proton collisions during the 2022 commissioning period as well as its expected performance in proton-proton and heavy-ion collisions for the remainder of the third LHC data-taking period (2022–2025)

    Beam-induced backgrounds measured in the ATLAS detector during local gas injection into the LHC beam vacuum

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    Inelastic beam-gas collisions at the Large Hadron Collider (LHC), within a few hundred metres of the ATLAS experiment, are known to give the dominant contribution to beam backgrounds. These are monitored by ATLAS with a dedicated Beam Conditions Monitor (BCM) and with the rate of fake jets in the calorimeters. These two methods are complementary since the BCM probes backgrounds just around the beam pipe while fake jets are observed at radii of up to several metres. In order to quantify the correlation between the residual gas density in the LHC beam vacuum and the experimental backgrounds recorded by ATLAS, several dedicated tests were performed during LHC Run 2. Local pressure bumps, with a gas density several orders of magnitude higher than during normal operation, were introduced at different locations. The changes of beam-related backgrounds, seen in ATLAS, are correlated with the local pressure variation. In addition the rates of beam-gas events are estimated from the pressure measurements and pressure bump profiles obtained from calculations. Using these rates, the efficiency of the ATLAS beam background monitors to detect beam-gas events is derived as a function of distance from the interaction point. These efficiencies and characteristic distributions of fake jets from the beam backgrounds are found to be in good agreement with results of beam-gas simulations performed with theFluka Monte Carlo programme

    Simultaneous energy and mass calibration of large-radius jets with the ATLAS detector using a deep neural network

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    The energy and mass measurements of jets are crucial tasks for the Large Hadron Collider experiments. This paper presents a new calibration method to simultaneously calibrate these quantities for large-radius jets measured with the ATLAS detector using a deep neural network (DNN). To address the specificities of the calibration problem, special loss functions and training procedures are employed, and a complex network architecture, which includes feature annotation and residual connection layers, is used. The DNN-based calibration is compared to the standard numerical approach in an extensive series of tests. The DNN approach is found to perform significantly better in almost all of the tests and over most of the relevant kinematic phase space. In particular, it consistently improves the energy and mass resolutions, with a 30% better energy resolution obtained for transverse momenta pT > 500 GeV

    Diferentes vias de administração da solução de fosfato monobásico e dibásico de sódio no preparo do cólon para colonoscopia rígida em cães Different routes in administration of sodium phosphate monobasic and dibasic solution in bowel preparation for rigid colonoscopy in dogs

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    Foram comparadas duas vias de administração, oral e retal, com a solução de fosfato monobásico e dibásico de sódio (NaP), juntamente com bisacodil via oral, no preparo do cólon para colonoscopia rígida em cães, para avaliar parâmetros clínicos, qualidade do preparo e variações dos eletrólitos fósforo, cálcio, potássio (K+) sódio (Na+) e magnésio (Mg+), além da creatinina, albumina e hemograma. Todos os eletrólitos apresentaram alterações, sendo significativa a queda nos níveis de K+ e Mg+. Não houve alterações eletrocardiográficas, e a redução da microbiota bacteriana foi confirmada nos dois grupos de administração da solução. Os resultados foram similares quanto à incidência de efeitos colaterais, porém a via retal apresentou facilidade na administração, menor retenção fecal no cólon, maior rapidez para realização da colonoscopia, com menor desperdício de tempo na lavagem e na aspiração do conteúdo fecal. O preparo intestinal com bisacodil oral e solução de NaP por via retal foi mais eficaz, podendo ser recomendado em cães que serão submetidos à colonoscopia.<br>The efficacy of oral and rectal administration of sodium phosphate monobasic and dibasic solution (NaP) combined with bisacodil per oral, as drugs to prepare the colon for rigid colonoscopy in dogs was compa1ed. Clinical parameters; colonic cleaning, plasma concentration of calcium, potassium (K+), sodium (Na+), magnesium (Mg+), creatinine, and albumin, and complete blood count were evaluated. In both groups, all electrolytes presented alterations, with significant reduction of the levels of K+ and Mg+, but there were no electrocardiographic alterations. No difference in the reduction of bacterial population was observed between the two groups. The results were similar regarding the incidence of side effects; however, the rectal route presented less fecal retention in colon and could get patients ready for the procedure faster. The preparation of bowel with bisacodil and NaP solution by rectal route was more effective and could be recommended for colonoscopy in dogs

    Sclerotherapy in extrahepatic portal venous obstruction.

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    One hundred and twenty two patients who presented with variceal bleeding as a result of extrahepatic portal vein obstruction (EHPO) were entered into the sclerotherapy programme with a mean follow up of 23.69 months (range four to 60 months). Eighteen (14.7%) patients were lost to follow up, three (2.4%) patients underwent surgery, and six (4.9%) patients died. Variceal obliteration was achieved in the remaining 95 patients requiring 5.4 (2.4) sessions of sclerotherapy (range 2-18). Seventeen episodes of upper gastrointestinal bleed occurred in 15 patients during sclerotherapy. Recurrence of oesophageal varices was seen in 15 patients. Ten patients developed bulbous gastric varices after obliteration. Major complications including perforation and strictures were seen more commonly in children. Sclerotherapy was associated with a significant reduction in the bleeding rate (bleeds/month/patient) as compared with the presclerotherapy period (p less than 0.001). Endoscopic sclerotherapy is an effective and safe modality in the prevention of variceal bleeds in patients with extrahepatic portal vein obstruction
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