299 research outputs found

    Study of the associated production of a Z boson and jets in pp collisions at sqrt(s) = 7 TeV at CMS

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    2011/2012In this thesis differential cross sections measurements of Z boson and jets associated production (Z + jets) will be presented; they are obtained by analyzing a large part of the 2011 dataset that corresponds to a total integrated luminosity of 4.89 1/fb. This type of processes are central in the physics program of LHC. The study of jets produced with Z provides a stringent and important test of perturbative QCD. In addition, a precise measurement of the Z + jets cross sections is crucial since these processes are a significant background in searches for new physics. This work is organized as follows. First an introduction to the SM theory, to the Z + jets physics and to the Monte Carlo generators is given, then a summary of the main features of the CMS detector is presented. The description of how the reconstruction and the identification of the particles is done in CMS, with a particular attention to the electron and jets, is reported, followed by the discussion about the performance of the electron reconstruction algorithms used in CMS. Finally the measurement of the differential cross sections for the Z + jets associated production and the obtained results are described.XXV Ciclo198

    Differential cross section measurements for the production of a W boson in association with jets in proton-proton collisions at sqrt(s) = 7 TeV

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    Measurements are reported of differential cross sections for the production of a W boson, which decays into a muon and a neutrino, in association with jets, as a function of several variables, including the transverse momenta (pTpT) and pseudorapidities of the four leading jets, the scalar sum of jet transverse momenta (HTHT), and the difference in azimuthal angle between the directions of each jet and the muon. The data sample of pp collisions at a centre-of-mass energy of 7 TeV was collected with the CMS detector at the LHC and corresponds to an integrated luminosity of 5.0 fb‚ąí1. The measured cross sections are compared to predictions from Monte Carlo generators, MadGraph + pythia and sherpa, and to next-to-leading-order calculations from BlackHat + sherpa. The differential cross sections are found to be in agreement with the predictions, apart from the pTpT distributions of the leading jets at high pTpT values, the distributions of the HTHT at high-HTHT and low jet multiplicity, and the distribution of the difference in azimuthal angle between the leading jet and the muon at low values

    Differential cross section measurements for the production of a W boson in association with jets in proton‚Äďproton collisions at ‚ąös = 7 TeV

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    Measurements are reported of differential cross sections for the production of a W boson, which decays into a muon and a neutrino, in association with jets, as a function of several variables, including the transverse momenta (pT) and pseudorapidities of the four leading jets, the scalar sum of jet transverse momenta (HT), and the difference in azimuthal angle between the directions of each jet and the muon. The data sample of pp collisions at a centre-of-mass energy of 7 TeV was collected with the CMS detector at the LHC and corresponds to an integrated luminosity of 5.0 fb[superscript ‚ąí1]. The measured cross sections are compared to predictions from Monte Carlo generators, MadGraph + pythia and sherpa, and to next-to-leading-order calculations from BlackHat + sherpa. The differential cross sections are found to be in agreement with the predictions, apart from the pT distributions of the leading jets at high pT values, the distributions of the HT at high-HT and low jet multiplicity, and the distribution of the difference in azimuthal angle between the leading jet and the muon at low values.United States. Dept. of EnergyNational Science Foundation (U.S.)Alfred P. Sloan Foundatio

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