A search for direct pair production of supersymmetric top squarks (${\tilde{t}}_1$) is presented, assuming the ${\tilde{t}}_1$ decays into a top quark and the lightest supersymmetric particle, ${\tilde{\chi }}_1^0$, and that both top quarks decay to purely hadronic final states. A total of 16 (4) events are observed compared to a predicted standard model background of ${13.5}_{-3.6}^{+3.7}({4.4}_{-1.3}^{+1.7})$ events in two signal regions based on $\int \mathcal{L}dt=4.7{\mathrm{fb}}^{-1}$ of $pp$ collision data taken at $\sqrt{s}=7\mathrm{TeV}$ with the ATLAS detector at the LHC. An exclusion region in the ${\tilde{t}}_1$ versus ${\tilde{\chi }}_1^0$ mass plane is evaluated: $370<m_{{\tilde{t}}_1}<465\mathrm{GeV}$ is excluded for $m_{{\tilde{\chi }}_1^0}\sim 0\mathrm{GeV}$ while $m_{{\tilde{t}}_1}=445\mathrm{GeV}$ is excluded for $m_{{\tilde{\chi }}_1^0}\le 50\mathrm{GeV}$.

• Received 7 August 2012

DOI:https://doi.org/10.1103/PhysRevLett.109.211802

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© 2012 CERN, for the ATLAS Collaboration