Search for New Phenomena in ttbar Events With Large Missing Transverse Momentum in Proton-Proton Collisions at √s = 7 TeV with the ATLAS Detector

ATLAS COLLABORATION, G. AAD, F. MONTICELLI, ET AL

PHYSICAL REVIEW LETTERS

AMER PHYSICAL SOC

Lugar: New York; Año: 2012 vol. 231 p. 1 - 23

0031-9007

A search for new phenomena in ttbar 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 fb^-1 of data collected with the ATLAS detector at the LHC. The search is carried out in the single-lepton channel, characterized by an isolated lepton of high transverse momentum, four or more jets and large missing transverse momentum. 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 GeV and 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.