288 research outputs found

    Search for new particles in events with energetic jets and large missing transverse momentum in proton-proton collisions at root s=13 TeV

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    A search is presented for new particles produced at the LHC in proton-proton collisions at root s = 13 TeV, using events with energetic jets and large missing transverse momentum. The analysis is based on a data sample corresponding to an integrated luminosity of 101 fb(-1), collected in 2017-2018 with the CMS detector. Machine learning techniques are used to define separate categories for events with narrow jets from initial-state radiation and events with large-radius jets consistent with a hadronic decay of a W or Z boson. A statistical combination is made with an earlier search based on a data sample of 36 fb(-1), collected in 2016. No significant excess of events is observed with respect to the standard model background expectation determined from control samples in data. The results are interpreted in terms of limits on the branching fraction of an invisible decay of the Higgs boson, as well as constraints on simplified models of dark matter, on first-generation scalar leptoquarks decaying to quarks and neutrinos, and on models with large extra dimensions. Several of the new limits, specifically for spin-1 dark matter mediators, pseudoscalar mediators, colored mediators, and leptoquarks, are the most restrictive to date.Peer reviewe

    Combined searches for the production of supersymmetric top quark partners in proton-proton collisions at root s=13 TeV

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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 13 TeV at the CERN LHC, corresponding to an integrated luminosity of 137 fb(-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 themodel, the combined result excludes a top squarkmass up to 1325 GeV for amassless neutralino, and a neutralinomass up to 700 GeV for a top squarkmass of 1150 GeV. Top squarks with masses from 145 to 295 GeV, for neutralino masses from 0 to 100 GeV, with a mass difference between the top squark and the neutralino in a window of 30 GeV 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 420 GeV

    Probing effective field theory operators in the associated production of top quarks with a Z boson in multilepton final states at root s=13 TeV

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    Observation of tW production in the single-lepton channel in pp collisions at root s=13 TeV

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    A measurement of the cross section of the associated production of a single top quark and a W boson in final states with a muon or electron and jets in proton-proton collisions at root s = 13 TeV is presented. The data correspond to an integrated luminosity of 36 fb(-1) collected with the CMS detector at the CERN LHC in 2016. A boosted decision tree is used to separate the tW signal from the dominant t (t) over bar background, whilst the subleading W+jets and multijet backgrounds are constrained using data-based estimates. This result is the first observation of the tW process in final states containing a muon or electron and jets, with a significance exceeding 5 standard deviations. The cross section is determined to be 89 +/- 4 (stat) +/- 12 (syst) pb, consistent with the standard model.Peer reviewe

    Measurements of the Electroweak Diboson Production Cross Sections in Proton-Proton Collisions at root s=5.02 TeV Using Leptonic Decays

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    The first measurements of diboson production cross sections in proton-proton interactions at a center-of-mass energy of 5.02 TeV are reported. They are based on data collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 302 pb(-1). Events with two, three, or four charged light leptons (electrons or muons) in the final state are analyzed. The WW, WZ, and ZZ total cross sections are measured as sigma(WW) = 37:0(-5.2)(+5.5) (stat)(-2.6)(+2.7) (syst) pb, sigma(WZ) = 6.4(-2.1)(+2.5) (stat)(-0.3)(+0.5)(syst) pb, and sigma(ZZ) = 5.3(-2.1)(+2.5)(stat)(-0.4)(+0.5) (syst) pb. All measurements are in good agreement with theoretical calculations at combined next-to-next-to-leading order quantum chromodynamics and next-to-leading order electroweak accuracy

    Measurement of the top quark mass using events with a single reconstructed top quark in pp collisions at root s=13 TeV

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    Abstract:A measurement of the top quark mass is performed using a data sample en-riched with single top quark events produced in thetchannel. The study is based on proton-proton collision data, corresponding to an integrated luminosity of 35.9 fb−1, recorded at√s= 13TeV by the CMS experiment at the LHC in 2016. Candidate events are selectedby requiring an isolated high-momentum lepton (muon or electron) and exactly two jets,of which one is identified as originating from a bottom quark. Multivariate discriminantsare designed to separate the signal from the background. Optimized thresholds are placedon the discriminant outputs to obtain an event sample with high signal purity. The topquark mass is found to be172.13+0.76−0.77GeV, where the uncertainty includes both the sta-tistical and systematic components, reaching sub-GeV precision for the first time in thisevent topology. The masses of the top quark and antiquark are also determined separatelyusing the lepton charge in the final state, from which the mass ratio and difference aredetermined to be0.9952+0.0079−0.0104and0.83+1.79−1.35GeV, respectively. The results are consistentwithCPTinvariance

    Search for a heavy Higgs boson decaying into two lighter Higgs bosons in the tau tau bb final state at 13 TeV

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    A search for a heavy Higgs boson H decaying into the observed Higgs boson h with a mass of 125 GeV and another Higgs boson h(S) is presented. The h and h(S) bosons are required to decay into a pair of tau leptons and a pair of b quarks, respectively. The search uses a sample of proton-proton collisions collected with the CMS detector at a center-of-mass energy of 13TeV, corresponding to an integrated luminosity of 137 fb(-1). Mass ranges of 240-3000 GeV for m(H) and 60-2800 GeV for m(hS) are explored in the search. No signal has been observed. Model independent 95% confidence level upper limits on the product of the production cross section and the branching fractions of the signal process are set with a sensitivity ranging from 125 fb (for m(H) = 240 GeV) to 2.7 fb (for m(H) = 1000 GeV). These limits are compared to maximally allowed products of the production cross section and the branching fractions of the signal process in the next-to-minimal supersymmetric extension of the standard model.Peer reviewe

    Impact of two atypical enteropeptides, Neuromedin U and extrapancreatic glucagon, on glucose homeostasis

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    L’épithélium intestinal assure trois grandes fonctions de barrière, de digestion/absorption des nutriments et de sécrétion d’entéro-hormones. Plus de 100 entéro-hormones ont été identifiées en un siècle, mais la plupart restent mal caractérisées. La fonction endocrine intestinale participe au maintien de l’homéostasie glucidique, notamment en induisant une sécrétion d’insuline par le pancréas. Cet axe intestin-pancréas est finement régulé par le système nerveux central. Une dérégulation de la sécrétion des hormones pancréatiques et intestinales participe à l’hyperglycémie chronique observée chez les sujets diabétiques. Une hyperglucagonémie est notamment impliquée dans l’équilibre glycémique instable des sujets diabétiques même quand ils ont subi une résection totale du pancréas. L’objectif de cette thèse a été de caractériser deux entéro-hormones, la Neuromédine U et le glucagon colique, puis de mettre en évidence leur implication dans le contrôle de l’homéostasie glucidique. Ce travail a nécessité le développement d’un modèle murin de pancréatectomie subtotale. Les résultats obtenus au cours de cette thèse mettent en évidence une production et une sécrétion de Neuromédine U (NMU) et de glucagon respectivement par l’intestin grêle proximal et par le colon. NMU participe au contrôle de la réponse glycémique post-prandiale en bloquant la vidange gastrique. En effet, NMU module les contractions de la paroi gastro-intestinale de manières directe et indirecte. Le glucagon est synthétisé par le colon en conditions physiologiques mais sa production et sa sécrétion sont augmentées après pancréatectomie.Ce travail démontre que les contractions de la paroi gastro-intestinale ont un impact sur la fonction de digestion/absorption des nutriments. En modulant ce paramètre, des analogues de NMU permettraient de diminuer l’hyperglycémie chez des sujets diabétiques. Par ailleurs, le développement de molécules capables d’inhiber la sécrétion colique de glucagon chez les sujets diabétiques permettrait d’améliorer leurs paramètres d’homéostasie glucidique. Ce travail contribue à replacer le tube digestif au centre du contrôle de l’homéostasie glucidique.Intestinal epithelium handles three main functions of barrier, nutrient digestion/absorption and enteropeptide secretion. In a century, technical improvements led to the identification of more than 100 enteropeptides, most of which are still poorly characterized. Intestinal endocrine secretions participate in maintaining glucose homeostasis, notably by inducing pancreatic insulin secretion. The gut-pancreas axis is tightly controlled by the central nervous system. Deregulation of pancreatic and intestinal peptides secretion participate in diabetic chronic hyperglycemia. An hyperglucagonemia is notably implicated in brittle glycemic control observed in diabetic subjects, even those who underwent a total pancreatectomy.The aim of this thesis was to characterize two enteropeptides, Neuromedin U and colonic glucagon, and to decipher their implication in glucose homeostasis. The development of a murine model of pancreatectomy has been necessary.Results obtained highlight a production and a secretion of Neuromedin U (NMU) and glucagon by the proximal small intestine and the colon respectively. NMU controls post-prandial glucose excursion by blocking gastric emptying via direct and indirect regulation of gastric wall contractions. Colonic glucagon is synthetized in physiological conditions but its production and secretion are increased following pancreatectomy.This study highlights how gut wall contractions are at play in the regulation of nutrient digestion/absorption. Targeting this parameter with NMU analogs may decrease diabetic hyperglycemia. Furthermore, development of colonic glucagon secretion might be of particular interest for the treatment of diabetic patients. This work demonstrate the prominent role of the gut in glucose homeostasis

    Bariatric surgery induces a new gastric mucosa phenotype with increased functional glucagon-like peptide-1 expressing cells

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    International audienceGlucagon-Like Peptide-1 (GLP-1) undergoes rapid inactivation by dipeptidyl peptidase-4 (DPP4) suggesting that target receptors may be activated by locally produced GLP-1. Here we describe GLP-1 positive cells in the rat and human stomach and found these cells co-expressing ghrelin or somatostatin and able to secrete active GLP-1 in the rats. In lean rats, a gastric load of glucose induces a rapid and parallel rise in GLP-1 levels in both the gastric and the portal veins. This rise in portal GLP-1 levels was abrogated in HFD obese rats but restored after vertical sleeve gastrectomy (VSG) surgery. Finally, obese rats and individuals operated on Roux-en-Y gastric bypass and SG display a new gastric mucosa phenotype with hyperplasia of the mucus neck cells concomitant with increased density of GLP-1 positive cells. This report brings to light the contribution of gastric GLP-1 expressing cells that undergo plasticity changes after bariatric surgeries, to circulating GLP-1 levels
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