A search for $t\bar{t}$ resonances with the ATLAS detector in 2.05 fb−1 of proton-proton collisions at $\sqrt{s} = 7~\mathrm{TeV}$

Abstract

A search for top quark pair resonances in final states containing at least one electron or muon has been performed with the ATLAS experiment at the CERN Large Hadron Collider. The search uses a data sample corresponding to an integrated luminosity of 2.05 fb−1, which was recorded in 2011 at a proton-proton centre-of-mass energy of 7 TeV. No evidence for a resonance is found and limits are set on the production cross-section times branching ratio to \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$t\bar{t}$\end{document} for narrow and wide resonances. For narrow Z′ bosons, the observed 95 % Bayesian credibility level limits range from 9.3 pb to 0.95 pb for masses in the range of mZ′=500 GeV to mZ′=1300 GeV. The corresponding excluded mass region for a leptophobic topcolour Z′ boson (Kaluza-Klein gluon excitation in the Randall-Sundrum model) is mZ′<880 GeV (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$m_{g_{\mathrm{KK}}} < 1130~ \mathrm{GeV}$\end{document}).

Improving estimates of the number of ‘fake’ leptons and other mis-reconstructed objects in hadron collider events: BoB’s your UNCLE

“…The estimate for the expected number of events that are fake is thenn F 11) where the ζ object is responsible for defining what is meant by a fake event. For example, if rr ≡ R and {rf, f r, f f } ≡ F then one would choose ζ 12 12 = ζ 21 21 = ζ 22 22 = 1, and all other components 0.…”

Search forZ′resonances decaying tott¯indilepton+Chatrchyan1, Khachatryan2, Sirunyan3 et al. 2013Phys. Rev. DSelf Cite400210View full textAdd to dashboardCite

“…Experiments seek to observe an excess beyond that predicted by the SM, typically in the distribution of the invariant mass of the t " t decay products. Searches in p " p collisions at the Tevatron and the early searches in pp collisions at the LHC by the ATLAS experiment have excluded a narrow-width, leptophobic Z 0 with a mass lower than 900 GeV [6][7][8]. The searches by the Compact Muon Solenoid (CMS) experiment at the LHC have excluded a narrow-width, leptophobic Z 0 in the mass range 1.3-1.5 TeV and in a narrow window around 1 TeV [9,10].…”

Search for Resonant Top-Antitop Production in the Lepton Plus Jets Decay Mode Using the Full CDF Data Set

“…This model explains the large mass of the top quark through the introduction of new strong dynamics and also predicts a vector particle (Z 0 boson), which couples primarily to the third generation of quarks and has no significant couplings to leptons. The existence of a narrow-width Z 0 boson PRL 110, 121802 (2013) P H Y S I C A L R E V I E W L E T T E R S week ending 22 MARCH 2013 121802-3 resonance (À Z 0 ¼ 0:012M Z 0 ) decaying to t " t pairs, using the leptophobic top-color model [18,19], has been searched for by both the CDF [13][14][15][16] and D0 [5,20,21] experiments at the Tevatron and also by the ATLAS [22][23][24] and CMS [25,26] experiments at the LHC. For resonance searches at the highest masses, the LHC experiments have superior sensitivity to the Tevatron due to the higher center-of-mass energy.…”