2,406 research outputs found

    Triggers for displaced decays of long-lived neutral particles in the ATLAS detector

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    A set of three dedicated triggers designed to detect long-lived neutral particles decaying throughout the ATLAS detector to a pair of hadronic jets is described. The efficiencies of the triggers for selecting displaced decays as a function of the decay position are presented for simulated events. The effect of pile-up interactions on the trigger efficiencies and the dependence of the trigger rate on instantaneous luminosity during the 2012 data-taking period at the LHC are discussedFil: Aad, G.. Albert Ludwigs UniversitĂ€t; AlemaniaFil: Abajyan, T.. Universitaet Bonn; AlemaniaFil: Abbott, B.. University of Oklahoma; Estados UnidosFil: Abdallah, J.. Universitat AutĂČnoma de Barcelona; EspañaFil: Abdel Khalek, S.. Universite Paris Sud; FranciaFil: Alconada Verzini, MarĂ­a Josefina. Consejo Nacional de Investigaciones CientĂ­ficas y TĂ©cnicas. Centro CientĂ­fico TecnolĂłgico Conicet - La Plata. Instituto de FĂ­sica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de FĂ­sica La Plata; ArgentinaFil: Alonso, Francisco. Consejo Nacional de Investigaciones CientĂ­ficas y TĂ©cnicas. Centro CientĂ­fico TecnolĂłgico Conicet - La Plata. Instituto de FĂ­sica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de FĂ­sica La Plata; ArgentinaFil: Anduaga, Xabier Sebastian. Consejo Nacional de Investigaciones CientĂ­ficas y TĂ©cnicas. Centro CientĂ­fico TecnolĂłgico Conicet - La Plata. Instituto de FĂ­sica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de FĂ­sica La Plata; ArgentinaFil: Dova, Maria Teresa. Consejo Nacional de Investigaciones CientĂ­ficas y TĂ©cnicas. Centro CientĂ­fico TecnolĂłgico Conicet - La Plata. Instituto de FĂ­sica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de FĂ­sica La Plata; ArgentinaFil: GonzĂĄlez Silva, MarĂ­a Laura. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de FĂ­sica; Argentina. Consejo Nacional de Investigaciones CientĂ­ficas y TĂ©cnicas; ArgentinaFil: Monticelli, Fernando Gabriel. Consejo Nacional de Investigaciones CientĂ­ficas y TĂ©cnicas. Centro CientĂ­fico TecnolĂłgico Conicet - La Plata. Instituto de FĂ­sica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de FĂ­sica La Plata; ArgentinaFil: Otero y Garzon, Gustavo Javier. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de FĂ­sica; Argentina. Consejo Nacional de Investigaciones CientĂ­ficas y TĂ©cnicas; ArgentinaFil: Piegaia, Ricardo Nestor. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de FĂ­sica; Argentina. Consejo Nacional de Investigaciones CientĂ­ficas y TĂ©cnicas; ArgentinaFil: Romeo, Gaston Leonardo. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de FĂ­sica; Argentina. Consejo Nacional de Investigaciones CientĂ­ficas y TĂ©cnicas; ArgentinaFil: Tripiana, Martin Fernando. Consejo Nacional de Investigaciones CientĂ­ficas y TĂ©cnicas. Centro CientĂ­fico TecnolĂłgico Conicet - La Plata. Instituto de FĂ­sica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de FĂ­sica La Plata; ArgentinaFil: Zhuang, X.. Ludwig Maximilians Universitat; AlemaniaFil: Zhuravlov, V.. Max-Planck Institut fĂŒr Physik; AlemaniaFil: Zieminska, D.. Indiana University; Estados UnidosFil: Zimin, N. I.. Joint Institute for Nuclear Research; RusiaFil: Zimmermann, R.. Universitaet Bonn; AlemaniaFil: Zimmermann, S.. Universitaet Bonn; AlemaniaFil: Zimmermann, S.. Albert Ludwigs UniversitĂ€t; AlemaniaFil: Ziolkowski, M.. UniversitĂ€t Siegen; AlemaniaFil: Zitoun, R.. UniversitĂ© de Savoie; FranciaFil: Ćœivković, L.. Columbia University; Estados UnidosFil: Zmouchko, V. V.. State Research Center Institute for High Energy Physics; RusiaFil: Zobernig, G.. University of Wisconsin; Estados UnidosFil: Zoccoli, A.. UniversitĂ  di Bologna; ItaliaFil: zur Nedden, M.. Humboldt University; AlemaniaFil: Zutshi, V.. Northern Illinois University; Estados Unido

    Small-Scale Structure of Spacetime: Bounds and Conjectures

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    This review consists of two parts. The first part establishes certain astrophysical bounds on the smoothness of classical spacetime. Some of the best bounds to date are based on the absence of vacuum Cherenkov radiation in ultrahigh-energy cosmic rays. The second part discusses possible implications of these bounds for the quantum structure of spacetime. One conjecture is that the fundamental length scale of quantum spacetime may be different from the Planck length.Comment: 20 pages; invited talk at the Third Mexican Meeting on Mathematical and Experimental Physics, September 10-14, 2007, El Colegio Nacional, Mexico City; v3: final versio

    Search for dark matter in events with a hadronically decaying W or Z boson and missing transverse momentum in pp collisions at √s=8  TeV with the ATLAS detector

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    A search is presented for dark matter pair production in association with a W or Z boson in pp collisions representing 20.3  fb−1 of integrated luminosity at s√=8  TeV using data recorded with the ATLAS detector at the Large Hadron Collider. Events with a hadronic jet with the jet mass consistent with a W or Z boson, and with large missing transverse momentum are analyzed. The data are consistent with the standard model expectations. Limits are set on the mass scale in effective field theories that describe the interaction of dark matter and standard model particles, and on the cross section of Higgs production and decay to invisible particles. In addition, cross section limits on the anomalous production of W or Z bosons with large missing transverse momentum are set in two fiducial regions

    Searches for heavy long-lived sleptons and R-hadrons with the ATLAS detector in pp collisions at √s=7 TeV

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    A search for long-lived particles is performed using a data sample of 4.7 fb(-1) from proton-proton collisions at a centre-of-mass energy √s = 7 TeV collected by the ATLAS detector at the LHC. No excess is observed above the estimated background and lower limits, at 95% confidence level, are set on the mass of the long-lived particles in different scenarios, based on their possible interactions in the inner detector, the calorimeters and the muon spectrometer. Long-lived staus in gauge-mediated SUSY-breaking models are excluded up to a mass of 300 GeV for tan ÎČ = 5-20. Directly produced long-lived sleptons are excluded up to a mass of 278 GeV. R-hadrons, composites of gluino (stop, sbottom) and light quarks, are excluded up to a mass of 985 GeV (683 GeV, 612 GeV) when using a generic interaction model. Additionally two sets of limits on R-hadrons are obtained that are less sensitive to the interaction model for R-hadrons. One set of limits is obtained using only the inner detector and calorimeter observables, and a second set of limits is obtained based on the inner detector alone

    Measurement of the flavour composition of dijet events in pp collisions at root s=7 TeV with the ATLAS detector

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    This paper describes a measurement of the flavour composition of dijet events produced in pp collisions at √s=7 TeV using the ATLAS detector. The measurement uses the full 2010 data sample, corresponding to an integrated luminosity of 39 pb−1. Six possible combinations of light, charm and bottom jets are identified in the dijet events, where the jet flavour is defined by the presence of bottom, charm or solely light flavour hadrons in the jet. Kinematic variables, based on the properties of displaced decay vertices and optimised for jet flavour identification, are used in a multidimensional template fit to measure the fractions of these dijet flavour states as functions of the leading jet transverse momentum in the range 40 GeV to 500 GeV and jet rapidity |y|<2.1. The fit results agree with the predictions of leading- and next-to-leading-order calculations, with the exception of the dijet fraction composed of bottom and light flavour jets, which is underestimated by all models at large transverse jet momenta. The ability to identify jets containing two b-hadrons, originating from e.g. gluon splitting, is demonstrated. The difference between bottom jet production rates in leading and subleading jets is consistent with the next-to-leading-order predictions

    Searches for heavy long-lived sleptons and R-hadrons with the ATLAS detector in pp collisions at √s=7 TeV

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    A search for long-lived particles is performed using a data sample of 4.7 fb−1 from proton–proton collisions at a centre-of-mass energy √s =7 TeV collected by the ATLAS detector at the LHC. No excess is observed above the estimated background and lower limits, at 95% conïŹdence level, are set on the mass of the long-lived particles in different scenarios, based on their possible interactions in the inner detector, the calorimeters and the muon spectrometer. Long-lived staus in gauge-mediated SUSY-breaking models are excluded up to a mass of 300 GeV for tanÎČ =5–20. Directly produced long-lived sleptons are excluded up to a mass of 278 GeV. R-hadrons, composites of gluino (stop, sbottom) and light quarks, are excluded up to a mass of 985 GeV (683 GeV, 612 GeV) when using a generic interaction model. Additionally two sets of limits on R-hadrons are obtained that are less sensitive to the interaction model for R-hadrons. One set of limits is obtained using only the inner detector and calorimeter observables, and a second set of limits is obtained based on the inner detector alone

    A search for prompt lepton-jets in pp collisions at √s=7 TeV with the ATLAS detector

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    We present a search for a light (mass <2 GeV) boson predicted by Hidden Valley supersymmetric models that decays into a final state consisting of collimated muons or electrons, denoted “lepton-jets”. The analysis uses 5 fb−1 of √s = 7 TeV proton–proton collision data recorded by the ATLAS detector at the Large Hadron Collider to search for the following signatures: single lepton-jets with at least four muons; pairs of lepton-jets, each with two or more muons; and pairs of lepton-jets with two or more electrons. This study finds no statistically significant deviation from the Standard Model prediction and places 95% confidence-level exclusion limits on the production cross section times branching ratio of light bosons for several parameter sets of a Hidden Valley model

    Measurement of the flavour composition of dijet events in pp collisions at √s=7 TeV with the ATLAS detector

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    This paper describes a measurement of the flavour composition of dijet events produced in pp collisions at s√=7 TeV using the ATLAS detector. The measurement uses the full 2010 data sample, corresponding to an integrated luminosity of 39 pb−1. Six possible combinations of light, charm and bottom jets are identified in the dijet events, where the jet flavour is defined by the presence of bottom, charm or solely light flavour hadrons in the jet. Kinematic variables, based on the properties of displaced decay vertices and optimised for jet flavour identification, are used in a multidimensional template fit to measure the fractions of these dijet flavour states as functions of the leading jet transverse momentum in the range 40 GeV to 500 GeV and jet rapidity |y|<2.1. The fit results agree with the predictions of leading- and next-to-leading-order calculations, with the exception of the dijet fraction composed of bottom and light flavour jets, which is underestimated by all models at large transverse jet momenta. The ability to identify jets containing two b-hadrons, originating from e.g. gluon splitting, is demonstrated. The difference between bottom jet production rates in leading and subleading jets is consistent with the next-to-leading-order predictions

    Measurement of long-range pseudorapidity correlations and azimuthal harmonics in sNN\sqrt{s_{\mathrm{NN}}} = 5.02 TeV proton-lead collisions with the ATLAS detector

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    Measurements of two-particle correlation functions and the first five azimuthal harmonics, v1v_1 to v5v_5, are presented, using 28 nb−1\mathrm{nb}^{-1} of pp+Pb collisions at a nucleon-nucleon center-of-mass energy of sNN=5.02\sqrt{s_{\mathrm{NN}}}=5.02 TeV measured with the ATLAS detector at the LHC. Significant long-range ``ridge-like'' correlations are observed for pairs with small relative azimuthal angle (âˆŁÎ”Ï•âˆŁ<π/3|\Delta\phi|<\pi/3) and back-to-back pairs (âˆŁÎ”Ï•âˆŁ>2π/3|\Delta\phi|>2\pi/3) over the transverse momentum range 0.4<pT<120.4<p_{\rm T}<12 GeV and in different intervals of event activity. The event activity is defined by either the number of reconstructed tracks or the total transverse energy on the Pb-fragmentation side. The azimuthal structure of such long-range correlations is Fourier decomposed to obtain the harmonics vnv_n as a function of pTp_{\rm T} and event activity. The extracted vnv_n values for n=2n=2 to 55 decrease with nn. The v2v_2 and v3v_3 values are found to be positive in the measured pTp_{\rm T} range. The v1v_1 is also measured as a function of pTp_{\rm T} and is observed to change sign around pT≈1.5−2.0p_{\rm T}\approx 1.5-2.0 GeV and then increase to about 0.1 for pT>4p_{\rm T}>4 GeV. The v2(pT)v_2(p_{\rm T}), v3(pT)v_3(p_{\rm T}) and v4(pT)v_4(p_{\rm T}) are compared to the vnv_n coefficients in Pb+Pb collisions at sNN=2.76\sqrt{s_{\mathrm{NN}}} =2.76 TeV with similar event multiplicities. Reasonable agreement is observed after accounting for the difference in the average pTp_{\rm T} of particles produced in the two collision systems.Comment: 21 pages plus author list + cover pages (34 pages total), 16 figures, submitted to Phys. Rev. C., All figures including auxiliary figures can be found at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2013-04
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