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Browsing by Author "ATLAS collaboration (3019 authors)"

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  • Rapidity gap cross sections measured with the ATLAS detector in $pp$ collisions at $\sqrt{s}=7$ TeV
    Publication . ATLAS collaboration (3019 authors); Aguilar-Saavedra, Juan Antonio; Amaral, Pedro; Anjos, Nuno; Carvalho, João; Castro, Nuno Filipe; Conde Muiño, Patricia; Do Valle Wemans, André; Fiolhais, Miguel; Gomes, Agostinho; Gonçalo, Ricardo; Jorge, Pedro; Lopes, Lourenco; Machado Miguens, Joana; Maio, Amélia; Maneira, José; Oliveira, Miguel Alfonso; Onofre, António; Palma, Alberto; Pina, João Antonio; Pinto, Belmiro; Santos, Helena; Saraiva, João; Silva, José; Soares, Mara; Veloso, Filipe; Wolters, Helmut
    Pseudorapidity gap distributions in proton-proton collisions at sqrt(s) = 7 TeV are studied using a minimum bias data sample with an integrated luminosity of 7.1 inverse microbarns. Cross sections are measured differentially in terms of Delta eta F, the larger of the pseudorapidity regions extending to the limits of the ATLAS sensitivity, at eta = +/- 4.9, in which no final state particles are produced above a transverse momentum threshold p_T Cut. The measurements span the region 0 < Delta eta F < 8 for 200 < p_T Cut < 800 MeV. At small Delta eta F, the data test the reliability of hadronisation models in describing rapidity and transverse momentum fluctuations in final state particle production. The measurements at larger gap sizes are dominated by contributions from the single diffractive dissociation process (pp -> Xp), enhanced by double dissociation (pp -> XY) where the invariant mass of the lighter of the two dissociation systems satisfies M_Y <~ 7 GeV. The resulting cross section is d sigma / d Delta eta F ~ 1 mb for Delta eta F >~ 3. The large rapidity gap data are used to constrain the value of the pomeron intercept appropriate to triple Regge models of soft diffraction. The cross section integrated over all gap sizes is compared with other LHC inelastic cross section measurements.
    2012-03-13Journal article Open access Show more
  • Search for anomaly-mediated supersymmetry breaking with the ATLAS detector based on a disappearing-track signature in $pp$ collisions at $\sqrt{s}=7$ TeV
    Publication . ATLAS collaboration (3019 authors); Aguilar-Saavedra, Juan Antonio; Amaral, Pedro; Anjos, Nuno; Carvalho, João; Castro, Nuno Filipe; Conde Muiño, Patricia; Do Valle Wemans, André; Fiolhais, Miguel; Gomes, Agostinho; Gonçalo, Ricardo; Jorge, Pedro; Lopes, Lourenco; Machado Miguens, Joana; Maio, Amélia; Maneira, José; Oliveira, Miguel Alfonso; Onofre, António; Palma, Alberto; Pina, João Antonio; Pinto, Belmiro; Santos, Helena; Saraiva, João; Silva, José; Soares, Mara; Veloso, Filipe; Wolters, Helmut
    In models of anomaly-mediated supersymmetry breaking (AMSB), the lightest chargino is predicted to have a lifetime long enough to be detected in collider experiments. This letter explores AMSB scenarios in pp collisions at sqrt(s) = 7 TeV by attempting to identify decaying charginos which result in tracks that appear to have few associated hits in the outer region of the tracking system. The search was based on data corresponding to an integrated luminosity of 1.02 fb^-1 collected with the ATLAS detector in 2011. The pT spectrum of candidate tracks is found to be consistent with the expectation from Standard Model background processes and constraints on the lifetime and the production cross section were obtained. In the minimal AMSB framework with m_3/2 < 32 TeV, m_0 < 1.5 TeV, tan(beta) = 5 and mu > 0, a chargino having mass below 92 GeV and a lifetime between 0.5 ns and 2 ns is excluded at 95% confidence level.
    2012-04-27Journal article Open access Show more
  • Search for heavy vector-like quarks coupling to light quarks in proton-proton collisions at $\sqrt{s}=7$ TeV with the ATLAS detector
    Publication . ATLAS collaboration (3019 authors); Aguilar-Saavedra, Juan Antonio; Amaral, Pedro; Anjos, Nuno; Carvalho, João; Castro, Nuno Filipe; Conde Muiño, Patricia; Do Valle Wemans, André; Fiolhais, Miguel; Gomes, Agostinho; Gonçalo, Ricardo; Jorge, Pedro; Lopes, Lourenco; Machado Miguens, Joana; Maio, Amélia; Maneira, José; Oliveira, Miguel Alfonso; Onofre, António; Palma, Alberto; Pina, João Antonio; Pinto, Belmiro; Santos, Helena; Saraiva, João; Silva, José; Soares, Mara; Veloso, Filipe; Wolters, Helmut
    This letter presents a search for singly produced vector-like quarks, Q, coupling to light quarks, q. The search is sensitive to both charged current (CC) and neutral current (NC) processes, p p --> Q q --> W q q' and p p --> Q q --> Z q q' with a leptonic decay of the vector gauge boson. In 1.04/fb of data taken in 2011 by the ATLAS experiment at a center-of-mass energy sqrt(s) = 7 TeV, no evidence of such heavy vector-like quarks is observed above the expected Standard Model background. Limits on the heavy vector-like quark production cross section times branching ratio as a function of mass m_Q are obtained. For a coupling kappa_(qQ) = v/m_Q, where v is the Higgs vacuum expectation value, 95% C.L. lower limits on the mass of a vector-like quark are set at 900 GeV and 760 GeV from CC and NC processes, respectively.
    2013-07-16Journal article Open access Show more