ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fassi, F., Ferrer, A., et al. (2013). Search for long-lived stopped R-hadrons decaying out of time with pp collisions using the ATLAS detector. Phys. Rev. D, 88(11), 112003–30pp.
Abstract: An updated search is performed for gluino, top squark, or bottom squark R-hadrons that have come to rest within the ATLAS calorimeter, and decay at some later time to hadronic jets and a neutralino, using 5.0 and 22.9 fb(-1) of pp collisions at 7 and 8 TeV, respectively. Candidate decay events are triggered in selected empty bunch crossings of the LHC in order to remove pp collision backgrounds. Selections based on jet shape and muon system activity are applied to discriminate signal events from cosmic ray and beam-halo muon backgrounds. In the absence of an excess of events, improved limits are set on gluino, stop, and sbottom masses for different decays, lifetimes, and neutralino masses. With a neutralino of mass 100 GeV, the analysis excludes gluinos with mass below 832 GeV (with an expected lower limit of 731 GeV), for a gluino lifetime between 10 μs and 1000 s in the generic R-hadron model with equal branching ratios for decays to q (q) over bar(chi) over tilde (0) and g (chi) over tilde (0). Under the same assumptions for the neutralino mass and squark lifetime, top squarks and bottom squarks in the Regge R-hadron model are excluded with masses below 379 and 344 GeV, respectively.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fassi, F., Ferrer, A., et al. (2013). Measurements of Higgs boson production and couplings in diboson final states with the ATLAS detector at the LHC. Phys. Lett. B, 726(1-3), 88–119.
Abstract: Measurements are presented of production properties and couplings of the recently discovered Higgs boson using the decays into boson pairs, H -> gamma gamma, H -> ZZ* -> 4l and H -> WW* -> l nu l nu. The results are based on the complete pp collision data sample recorded by the ATLAS experiment at the CERN Large Hadron Collider at centre-of-mass energies of root s = 7 TeV and root s = 8 TeV, corresponding to an integrated luminosity of about 25 fb(-1). Evidence for Higgs boson production through vector-boson fusion is reported. Results of combined fits probing Higgs boson couplings to fermions and bosons, as well as anomalous contributions to loop-induced production and decay modes, are presented. All measurements are consistent with expectations for the Standard Model Higgs boson.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fassi, F., Ferrer, A., et al. (2014). Measurement of the mass difference between top and anti-top quarks in pp collisions at root s=7 TeV using the ATLAS detector. Phys. Lett. B, 728, 363–379.
Abstract: A measurement of the mass difference between top and anti-top quarks is presented. In a 4.7 fb(-1) data sample of proton-proton collisions at root s = 7 TeV recorded with the ATLAS detector at the LHC, events consistent with t (t) over bar production and decay into a single charged lepton final state are reconstructed. For each event, the mass difference between the top and anti-top quark candidate is calculated. A two b-tag requirement is used in order to reduce the background contribution. A maximum likelihood fit to these per-event mass differences yields Delta m = m(t) – m((t) over bar) = 0.67 +/- 0.61 (stat) +/- 0.41 (syst) GeV, consistent with CPT invariance.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fassi, F., Ferrer, A., et al. (2014). Search for new phenomena in photon plus jet events collected in proton-proton collisions at root s=8 TeV with the ATLAS detector. Phys. Lett. B, 728, 562–578.
Abstract: This Letter describes a model-independent search for the production of new resonances in photon + jet (gamma + jet) events using 20 fb(-1) of proton-proton LHC data recorded with the ATLAS detector at a centre-of-mass energy of root s = 8 TeV. The gamma + jet mass distribution is compared to a background model fit from data; no significant deviation from the background-only hypothesis is found. Limits are set at 95% credibility level on generic Gaussian-shaped signals and two benchmark phenomena beyond the Standard Model: non-thermal quantum black holes and excited quarks. Non-thermal quantum black holes are excluded below masses of 4.6 TeV and excited quarks are excluded below masses of 3.5 TeV.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fassi, F., Ferrer, A., et al. (2014). Search for Dark Matter in Events with a Hadronically Decaying W or Z Boson and Missing Transverse Momentum in pp Collisions at root s=8 TeV with the ATLAS Detector. Phys. Rev. Lett., 112(4), 041802–17pp.
Abstract: 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 root 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.
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