2 research outputs found

    Measurements of the charge asymmetry in top-quark pair production in the dilepton final state at s √ =8  TeV with the ATLAS detector

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    Measurements of the top-antitop quark pair production charge asymmetry in the dilepton channel, characterized by two high-pT leptons (electrons or muons), are presented using data corresponding to an integrated luminosity of 20.3  fb−1 from pp collisions at a center-of-mass energy s√=8  TeV collected with the ATLAS detector at the Large Hadron Collider at CERN. Inclusive and differential measurements as a function of the invariant mass, transverse momentum, and longitudinal boost of the ttÂŻ system are performed both in the full phase space and in a fiducial phase space closely matching the detector acceptance. Two observables are studied: AℓℓC based on the selected leptons and AttÂŻC based on the reconstructed ttÂŻ final state. The inclusive asymmetries are measured in the full phase space to be AℓℓC=0.008±0.006 and AttÂŻC=0.021±0.016, which are in agreement with the Standard Model predictions of AℓℓC=0.0064±0.0003 and AttÂŻC=0.0111±0.0004

    Dark matter constraints from observations of 25 Milky\ua0Way satellite galaxies with the Fermi Large Area Telescope

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    The dwarf spheroidal satellite galaxies of the Milky Way are some of the most dark-matter-dominated objects known. Due to their proximity, high dark matter content, and lack of astrophysical backgrounds, dwarf spheroidal galaxies are widely considered to be among the most promising targets for the indirect detection of dark matter via \u3b3 rays. Here we report on \u3b3-ray observations of 25 Milky Way dwarf spheroidal satellite galaxies based on 4 years of Fermi Large Area Telescope (LAT) data. None of the dwarf galaxies are significantly detected in \u3b3 rays, and we present \u3b3-ray flux upper limits between 500 MeV and 500 GeV. We determine the dark matter content of 18 dwarf spheroidal galaxies from stellar kinematic data and combine LAT observations of 15 dwarf galaxies to constrain the dark matter annihilation cross section. We set some of the tightest constraints to date on the annihilation of dark matter particles with masses between 2 GeV and 10 TeV into prototypical standard model channels. We find these results to be robust against systematic uncertainties in the LAT instrument performance, diffuse \u3b3-ray background modeling, and assumed dark matter density profile
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