The lighter mass eigenstate (${\tilde{t}}_1$) of the two top squarks, the scalar superpartners of the top quark, is extremely difficult to discover if it is almost degenerate with the lightest neutralino (${\tilde{\chi }}_1^0$), the lightest stable supersymmetric particle in the R-parity conserving supersymmetry. The current experimental bound on ${\tilde{t}}_1$ mass in this scenario stands only around 200 GeV. For such a light ${\tilde{t}}_1$, the heavier top squark (${\tilde{t}}_2$) can also be around the TeV scale. Moreover, the high value of the Higgs ($h$) mass prefers the left- and right-handed top squarks to be highly mixed, allowing the possibility of a considerable branching ratio for ${\tilde{t}}_2\to {\tilde{t}}_{1}h$ and ${\tilde{t}}_2\to {\tilde{t}}_{1}Z$. In this paper, we explore the above possibility together with the pair production of ${\tilde{t}}_2$ ${\tilde{t}}_2^{*}$, giving rise to the spectacular $\mathrm{\text{diboson}}+\mathrm{\text{missing}}$ transverse energy final state. For an approximately 1 TeV ${\tilde{t}}_2$ and a few hundred GeV ${\tilde{t}}_1$ the final state particles can be moderately boosted, which encourages us to propose a novel search strategy employing the jet substructure technique to tag the boosted $h$ and $Z$. The reconstruction of the $h$ and $Z$ momenta also allows us to construct the stransverse mass $M_{T2}$, providing an additional efficient handle to fight the backgrounds. We show that a $4–5\sigma$ signal can be observed at the 14 TeV LHC for $\sim 1\mathrm{TeV}$ ${\tilde{t}}_2$ with $100{\mathrm{fb}}^{-1}$ integrated luminosity.

• Received 14 August 2013

DOI:https://doi.org/10.1103/PhysRevD.88.115013