2,329 research outputs found

    Studies of DVCS and photoproduction of photons at high t with the H1 Detector

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    The diffractive scattering of photon off proton γ(∗)p→γY\gamma^{(*)} p \to \gamma Y (where YY denotes the proton dissociative system or the elastically scattered proton) is measured in two different kinematic regimes at high energy with the H1 detector at HERA. i) the process is studied for the first time at large transverse photon momentum ptγ>2p_t^{\gamma} > 2 GeV in photoproduction regime (Q2<0.01Q^2 < 0.01 GeV2^2)and photon-proton c.m.s. energy 175<W<247GeV175 < W < 247 {\rm GeV}. The cross section is measured differentially in tt and in \xpom. The measurement is compared to a LL BFKL prediction of QCD. ii) in electroproduction, the Deeply Virtual Compton Scattering (DVCS) γ∗p→γp\gamma^* p \to \gamma p cross section has been measured more precisely and in an extended kinematic domain: at photon virtualities 4<Q2<804<Q^2<80 GeV2^2 and 30<W<14030<W<140 GeV. The measurement is compared to NLO QCD calculations using the DGLAP approximation and to Colour Dipole model predictions.Comment: Contribution to the Proceedings of International Europhysics Conference on High Energy Physics EPS, July 17th-23rd 2003, Aachen, German

    Revisiting QCD Fits in Diffractive DIS

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    A new method of extracting diffractive parton distributions is presented which avoids the use of Regge theory ansatz and is in much closer relation with the factorisation theorem for diffractive hard processes

    Search for supersymmetry in events with opposite-sign dileptons and missing transverse energy using an artificial neural network

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    In this paper, a search for supersymmetry (SUSY) is presented in events with two opposite-sign isolated leptons in the final state, accompanied by hadronic jets and missing transverse energy. An artificial neural network is employed to discriminate possible SUSY signals from a standard model background. The analysis uses a data sample collected with the CMS detector during the 2011 LHC run, corresponding to an integrated luminosity of 4.98  fb-1 of proton-proton collisions at the center-of-mass energy of 7 TeV. Compared to other CMS analyses, this one uses relaxed criteria on missing transverse energy (E̸T>40  GeV) and total hadronic transverse energy (HT>120  GeV), thus probing different regions of parameter space. Agreement is found between standard model expectation and observations, yielding limits in the context of the constrained minimal supersymmetric standard model and on a set of simplified model

    Un nuevo paradigna relacional: las vinculaciones inter-sectoriales en América Latina

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    Mediante el presente trabajo pretendo reflexionar sobre el fenómeno de aparición, reproducción y transformación de Organizaciones Sociales tendientes al Desarrollo Humano en América Latina. Como instrumentos de abordaje tomaré ciertas nociones elaboradas desde lo que podría denominarse Teoría Crítica Periférica. Me refiero aquí a aquellas elaboraciones teóricas que, habiendo surgido en los márgenes del sistema científico hegemónico occidental, aportan un conjunto de consideraciones conceptuales particularmente pertinentes para explicar los complejos procesos de transformación de la región latinoamericana. Por tanto, tomaré elementos de la Escuela de Tartú para aproximarme a una concepción dinámica del desarrollo socio-cultural; y ciertas elaboraciones del pensamiento crítico latinoamericano para abordar la dimensión ideológica de este proceso en la región.Facultad de Periodismo y Comunicación Socia

    Search for narrow resonances using the dijet mass spectrum in pp collisions at sqrt(s) = 8 TeV

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    Results are presented of a search for the production of new particles decaying to pairs of partons (quarks, antiquarks, or gluons), in the dijet mass spectrum in proton-proton collisions at sqrt(s) = 8 TeV. The data sample corresponds to an integrated luminosity of 4.0 inverse femtobarns, collected with the CMS detector at the LHC in 2012. No significant evidence for narrow resonance production is observed. Upper limits are set at the 95% confidence level on the production cross section of hypothetical new particles decaying to quark-quark, quark-gluon, or gluon-gluon final states. These limits are then translated into lower limits on the masses of new resonances in specific scenarios of physics beyond the standard model. The limits reach up to 4.8 TeV, depending on the model, and extend previous exclusions from similar searches performed at lower collision energies. For the first time mass limits are set for the Randall-Sundrum graviton model in the dijet channel

    Determination of the top-quark pole mass and strong coupling constant from the ttbar production cross section in pp collisions at sqrt(s) = 7 TeV

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    The inclusive cross section for top-quark pair production measured by the CMS experiment in proton-proton collisions at a center-of-mass energy of 7 TeV is compared to the QCD prediction at next-to-next-to-leading order with various parton distribution functions to determine the top-quark pole mass, mtpolem_t^{pole}, or the strong coupling constant, αS\alpha_S. With the parton distribution function set NNPDF2.3, a pole mass of 176.7−2.8+3.0^{+3.0}_{-2.8} GeV is obtained when constraining αS\alpha_S at the scale of the Z boson mass, mZm_Z, to the current world average. Alternatively, by constraining mtpolem_t^{pole} to the latest average from direct mass measurements, a value of αS(mZ)\alpha_S(m_Z) = 0.1151−0.0027+0.0028^{+0.0028}_{-0.0027} is extracted. This is the first determination of αS\alpha_S using events from top-quark production

    Transverse momentum spectra of b jets in pPb collisions at sqrt(s[NN]) = 5.02 TeV

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    We present a measurement of b jet transverse momentum (pt) spectra in proton-lead (pPb) collisions using a dataset corresponding to about 35 inverse nanobarns collected with the CMS detector at the LHC. Jets from b quark fragmentation are found by exploiting the long lifetime of hadrons containing a b quark through tagging methods using distributions of the secondary vertex mass and displacement. Extracted cross sections for b jets are scaled by the effective number of nucleon-nucleon collisions and are compared to a reference obtained from PYTHIA simulations of pp collisions. The PYTHIA-based estimate of the nuclear modification factor is found to be 1.22 +/- 0.15 (stat + syst pPb) +/- 0.27 (syst PYTHIA) averaged over all jets with pt between 55 and 400 GeV/c and with abs(eta[lab]) < 2. We also compare this result to predictions from models using perturbative calculations in quantum chromodynamics

    Search for the associated production of the Higgs boson with a top-quark pair

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    A search for the standard model Higgs boson produced in association with a top-quark pair (t tbar H) is presented, using data samples corresponding to integrated luminosities of up to 5.1 inverse femtobarns and 19.7 inverse femtobarns collected in pp collisions at center-of-mass energies of 7 TeV and 8 TeV respectively. The search is based on the following signatures of the Higgs boson decay: H to hadrons, H to photons, and H to leptons. The results are characterized by an observed t tbar H signal strength relative to the standard model cross section, mu = sigma/sigma[SM], under the assumption that the Higgs boson decays as expected in the standard model. The best fit value is mu = 2.8 +/- 1.0 for a Higgs boson mass of 125.6 GeV
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