UC Santa Cruz

A search is presented for direct top squark pair production using events with at least two leptons including a same-flavour opposite-sign pair with invariant mass consistent with the Z$$Z$$ boson mass, jets tagged as originating from b$$b$$-quarks and missing transverse momentum. The analysis is performed with proton–proton collision data at s=8TeV$$\sqrt{s}=8{\hbox {\ TeV}}$$ collected with the ATLAS detector at the LHC in 2012 corresponding to an integrated luminosity of 20.3 fb-1$$^{-1}$$. No excess beyond the Standard Model expectation is observed. Interpretations of the results are provided in models based on the direct pair production of the heavier top squark state (t~2$$\tilde{t}_2$$) followed by the decay to the lighter top squark state (t~1$$\tilde{t}_1$$) via t~2→Zt~1$$\tilde{t}_2 \rightarrow Z\tilde{t}_1$$, and for t~1$$\tilde{t}_1$$ pair production in natural gauge-mediated supersymmetry breaking scenarios where the neutralino (χ~10$$\tilde{\chi }^0_1$$) is the next-to-lightest supersymmetric particle and decays producing a Z$$Z$$ boson and a gravitino (G~$$\tilde{G}$$) via the χ~10→ZG~$$\tilde{\chi }^0_1 \rightarrow Z\tilde{G}$$ process.