Search for New Phenomena in $t\bar{t}$ Events With Large Missing Transverse Momentum in Proton-Proton Collisions at $\sqrt{s}=7$ TeV with the ATLAS Detector

• Main Author: ATLAS collaboration (3017 authors)
• Publication Date: 2011
• Other Authors: Aguilar-Saavedra, Juan Antonio, Amaral, Pedro, Anjos, Nuno, Carvalho, Joao, Castro, Nuno Filipe, Conde Muino, Patricia, Do Valle Wemans, Andre, Fiolhais, Miguel, Gomes, Agostinho, Goncalo, Ricardo, Jorge, Pedro, Lopes, Lourenco, Machado Miguens, Joana, Maio, Amelia, Maneira, Jose, Oliveira, Miguel Alfonso, Onofre, Antonio, Palma, Alberto, Pina, Joao Antonio, Pinto, Belmiro, Santos, Helena, Saraiva, Joao, Silva, Jose, Soares, Mara, Veloso, Filipe, Wolters, Helmut
• Format: Article
• Language: eng
• Source: Repositórios Científicos de Acesso Aberto de Portugal (RCAAP)
• Download full: http://dx.doi.org/10.1103/PhysRevLett.108.041805; http://hdl.handle.net/10400.26/26042

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.