Search for exotic same-sign dilepton signatures (b' quark, T_{5/3} and four top quarks production) in 4.7/fb of pp collisions at sqrt{s}=7 TeV with the ATLAS detector

We present a search for exotic processes --- pair production of down-type heavy quarks (b'), single and pair production of heavy top quark partners (T_{5/3}), and production of events containing four top quarks (ttbarttbar) --- in pp collisions at sqrt{s}=7 TeV recorded with the ATLAS detector at the Large Hadron Collider. Events are selected with two isolated leptons (e or mu) having the same electric charge, large missing transverse momentum, at least two jets, including at least one b-tagged jet, and a large overall transverse momentum. In a data sample of 4.7/fb, four events are observed with an expected background of 5.6+-1.7 events. The corresponding lower limit on both the b' and T_{5/3} mass is 0.67 TeV at 95% confidence level, when produced in pairs. When including the single production mechanism, limits on T_{5/3} production are 0.68 TeV and 0.70 TeV for a coupling constant of the tWT_{5/3} vertex equal to 1 and 3, respectively. The upper limit on the four top quarks production cross section is 61 fb at 95% confidence level.