1,721,202 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
QCD tests in collisions at TeV using the ATLAS detector at the LHC
No full textThe Large Hadron Collider facility at CERN, and in particular the ATLAS detector, have provided a testing ground for high energy physics at a level which couldn't be explored in previous experiments. It has not only increased the centre-of-mass energy to the up to now highest value of TeV but also has had an excellent luminosity performance during these years of data taking. This has been especially important for the discovery of the Higgs boson, as well as for allowing searches of new physics and studies of the properties of, up to now, poorly known final states as production. In this thesis, data taken during the year 2011 have been analyzed to probe the strong sector of the Standard Model. The parton shower and hadronisation models have been tested in this thesis by means of the measurement of jet shapes in final states. Relying on the top-quark decays and the subsequent boson hadronic decays , samples with very high purity of - and light-quark induced jets have been selected. This fact, together with the fine granularity of the ATLAS calorimeter system, has allowed us to compare -jet shapes with those of light jets (ATLAS Collaboration, Eur. Phys. J. C \textbf{73} 2676 (2013)) and to determine the -quark mass from the so-called angular screening effects, clearly visible in these data (J. Llorente and J. C., Nucl. Phys. B \textbf{889} 401 (2014)). Furthermore, -jets are found to be broader than light jets and therefore -jet shapes may be used for tagging purposes. The value of the strong coupling constant at the -pole scale has also been measured in this thesis. This constant plays a key role in our understanding of nature at the subatomic scale, as it determines the strength of gluon radiation, as well as being responsible for the stability of nuclear matter. We have selected a sample of multijet events by demanding the scalar sum of transverse momenta of the two leading jets to be greater than 500 GeV while the transverse momenta of the subleading jets is required to be above 50 GeV. All jets are required to lie in the central part of the calorimeter, i.e. . We have performed a measurement of transverse energy-energy correlations, which are the natural extension of the energy-energy correlation function which was popular in colliders at PETRA-PEP and LEP-SLC energies. We have performed a comparison between the data (ATLAS Collaboration, arXiv:1508.01579 [hep-ex]) with NLO pQCD calculations (A. A., F. B., J. Llorente and W. W., Phys. Rev. D \textbf{86} 114017 (2012)) which allows us to determine \alpha_s(m_Z) = 0.1173 \pm 0.0010 \mbox{ (exp.)} ^{+0.0065}_{-0.0026} \mbox{ (theo.)}
High- experimental results on QCD
No full textQCD measurements at high transverse momentum by ATLAS and CMS are presented
High- experimental results on QCD
No full textMeasurements by the ATLAS and CMS Collaborations, sensitive to different aspects of the QCD modelling, are presented. This includes the production of jets, inclusively and in association with bosons; as well as the production of photon pairs and the fragmentation of heavy quarks into hadrons. The measurements are compared to fixed-order perturbative predictions where available, as well as to Monte Carlo simulations including different algorithms for the matrix element calculation, the parton shower emissions and the hadronisation model. Determinations of the parton distribution functions inside the proton are also presented by both Collaborations
QCD tests in pp collisions at [raíz] s = 7 TeV using the ATLAS detector at the LHC
No full textTesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física Teórica. Fecha de lectura: 23-11-201
QCD measurements in ATLAS
No full textSeveral measurements in jet and photon physics are presented. The jet physics results include measurements of jet cross sections as well as various measurements on jet substructure and the precise determination of the strong coupling constant. Photon results include the measurements of several processes involving photons (inclusive, diphoton, photon + jet
Measurement of Transverse Energy-Energy Correlations and heavy-flavour jet fragmentation with the ATLAS detector
No full textIn this talk, we present measurements of jet energy-energy correlations and jet fragmentation properties using data collected by the ATLAS experiment at TeV. Measurements of transverse energy-energy correlations and their associated azimuthal asymmetries in multi-jet events are compared to next-to-leading-order perturbative QCD calculations and provide a precision test of QCD at large momentum transfers. The strong coupling constant is extracted from these data at different scale regimes. For jet fragmentation, we present a measurement of the fragmentation properties of b-quark initiated jets, studied using charged B mesons. This analysis provides key measurements with which to better understand the fragmentation functions of heavy quarks. Both results are corrected for detector effects and compared to several Monte Carlo predictions with different parton shower and hadronisation models
High- results and parton density functions from ATLAS.
No full textThe ATLAS detector at the LHC is an ideal experiment to rigorously test QCD in a large variety of final states. This talk will focus on recent results over a wide range of energies, which are particularly sensitive to parton density functions. We will review results with high- jets, photons and vector bosons. We will then discuss fits to determine parton distribution functions (PDFs) using these diverse sets of measurements from the ATLAS experiment. These ATLAS measurements are used in combination with deep-inelastic scattering data from HERA. Particular attention is paid to the correlation of systematic uncertainties within and between the various ATLAS data sets and to the impact of model, theoretical and parameterisation uncertainties. Finally, we will also present results on the determination of $\alpha_s
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