16 research outputs found

    Search for jet extinction in the inclusive jet-pT spectrum from proton-proton collisions at s=8 TeV

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    Published by the American Physical Society under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published articles title, journal citation, and DOI.The first search at the LHC for the extinction of QCD jet production is presented, using data collected with the CMS detector corresponding to an integrated luminosity of 10.7  fb−1 of proton-proton collisions at a center-of-mass energy of 8 TeV. The extinction model studied in this analysis is motivated by the search for signatures of strong gravity at the TeV scale (terascale gravity) and assumes the existence of string couplings in the strong-coupling limit. In this limit, the string model predicts the suppression of all high-transverse-momentum standard model processes, including jet production, beyond a certain energy scale. To test this prediction, the measured transverse-momentum spectrum is compared to the theoretical prediction of the standard model. No significant deficit of events is found at high transverse momentum. A 95% confidence level lower limit of 3.3 TeV is set on the extinction mass scale

    Measurement of the inclusive production cross sections for forward jets and for dijet events with one forward and one central jet in pp collisions at sqrt(s) = 7 TeV

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    The inclusive production cross sections for forward jets, as well for jets in dijet events with at least one jet emitted at central and the other at forward pseudorapidities, are measured in the range of transverse momenta pt = 35-150 GeV/c in proton-proton collisions at sqrt(s) = 7 TeV by the CMS experiment at the LHC. Forward jets are measured within pseudorapidities 3.2<|eta|<4.7, and central jets within the |eta|<2.8 range. The double differential cross sections with respect to pt and eta are compared to predictions from three approaches in perturbative quantum chromodynamics: (i) next-to-leading-order calculations obtained with and without matching to parton-shower Monte Carlo simulations, (ii) PYTHIA and HERWIG parton-shower event generators with different tunes of parameters, and (iii) CASCADE and HEJ models, including different non-collinear corrections to standard single-parton radiation. The single-jet inclusive forward jet spectrum is well described by all models, but not all predictions are consistent with the spectra observed for the forward-central dijet events.Comment: Submitted to the Journal of High Energy Physic

    Searches for electroweak neutralino and chargino production in channels with Higgs, Z, and W bosons in pp collisions at 8 TeV

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    Searches for supersymmetry (SUSY) are presented based on the electroweak pair production of neutralinos and charginos, leading to decay channels with Higgs, Z, and W bosons and undetected lightest SUSY particles (LSPs). The data sample corresponds to an integrated luminosity of about 19.5 fb(-1) of proton-proton collisions at a center-of-mass energy of 8 TeV collected in 2012 with the CMS detector at the LHC. The main emphasis is neutralino pair production in which each neutralino decays either to a Higgs boson (h) and an LSP or to a Z boson and an LSP, leading to hh, hZ, and ZZ states with missing transverse energy (E-T(miss)). A second aspect is chargino-neutralino pair production, leading to hW states with E-T(miss). The decays of a Higgs boson to a bottom-quark pair, to a photon pair, and to final states with leptons are considered in conjunction with hadronic and leptonic decay modes of the Z and W bosons. No evidence is found for supersymmetric particles, and 95% confidence level upper limits are evaluated for the respective pair production cross sections and for neutralino and chargino mass values

    Fitting to magnetoresistance under weak localization in three dimensions

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    We discuss a number of suggested explanations for observed discrepancies between theories of the quantum corrections to conduction, and recent magnetoresistance experiments on bulk metallic glasses. We emphasize the importance of competing effects, particularly the influence of magnetic impurities. Data showing these effects are presented and analyzed using a theory of Béal-Monod and Weiner to account for the direct magnetoresistance from the spin scattering and the magnetic field dependence of the spin-flip dephasing rate. Throughout, we provide useful numerical procedures for the efficient evaluation of the theoretical expressions used in analyzing such data, and point out that some theoretical expressions must be altered when considering strongly enhanced paramagnetic systems.Ce travail étudie en détail les différentes explications présentement proposées qui tentent d'expliquer les écarts observés entre les théories reliées aux corrections quantiques présentent dans les phénomènes de conduction des matériaux désordonnés et les récents résultats expérimentaux touchant la magnétorésistance des verres métalliques amorphes. Nous soulignons l'importance de divers effets compétitifs et en particulier de la forte influence des impuretés magnétiques. Pour démontrer celle-ci, nous présentons de nouveaux résultats relatifs à la présence de telles impuretés et les analysons en utilisant la théorie de Béal-Monod et Weiner qui permet de tenir compte de la magnétorésistance directement reliée à la diffusion des spins et à la dépendance en champ du taux de déphasage du renversement de ceux-ci. Tout au long de l'article nous présentons certaines techniques numériques qui permettent l'évaluation rapide et efficace des expressions théoriques nécessaire à l'analyse de tels résultats. Finalement, nous montrons que certaines expressions théoriques doivent être modifiées lorsque des systèmes fortement paramagnétiques sont étudiés
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