Search for direct top squark pair production in events with a Z boson, b-jets and missing transverse momentum in sqrt(s)=8 TeV pp collisions with the ATLAS detector

Abstract

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 $Z$ boson mass, jets tagged as originating from $b$-quarks and missing transverse momentum. The analysis is performed with proton-proton collision data at $\sqrt{s}=8$ TeV collected with the ATLAS detector at the LHC in 2012 corresponding to an integrated luminosity of 20.3 fb${}^{-1}$. 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 (${\tilde{t}}_2$) followed by the decay to the lighter top squark state (${\tilde{t}}_1$) via ${\tilde{t}}_2\to Z{\tilde{t}}_1$, and for ${\tilde{t}}_1$ pair production in natural gauge-mediated supersymmetry breaking scenarios where the neutralino (${\tilde{\chi }}_1^0$) is the next-to-lightest supersymmetric particle and decays producing a $Z$ boson and a gravitino ($\tilde{G}$) via the ${\tilde{\chi }}_1^0\to Z\tilde{G}$ process.

14 pages plus author list (29 pages total), 6 figures, 1 table, submitted to EPJC, All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/SUSY-2013-08/

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