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Summary: Search for New Phenomena in tt Events with Large Missing Transverse Momentum
in Proton-Proton Collisions at
ffiffiffi
s
p
¼ 7 TeV with the ATLAS Detector
G. Aad et al.*
(ATLAS Collaboration)
(Received 22 September 2011; published 26 January 2012)
A search for new phenomena in t"t events with large missing transverse momentum in proton-proton
collisions at a center-of-mass energy of 7 TeV is presented. The measurement is based on 1:04 fbÀ1 of
data collected with the ATLAS detector at the LHC. Contributions to this final state may arise from a
number of standard model extensions. The results are interpreted in terms of a model where new top-quark
partners are pair produced and each decay to an on-shell top (or antitop) quark and a long-lived undetected
neutral particle. The data are found to be consistent with standard model expectations. A limit at 95%
confidence level is set excluding a cross section times branching ratio of 1.1 pb for a top-partner mass of
420 GeVand a neutral particle mass less than 10 GeV. In a model of exotic fourth generation quarks, top-
partner masses are excluded up to 420 GeV and neutral particle masses up to 140 GeV.
DOI: 10.1103/PhysRevLett.108.041805 PACS numbers: 14.65.Jk, 12.60.Ài, 13.85.Rm
The top quark holds great promise as a probe for new
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