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Top Squark Searches Using Dilepton Invariant Mass Distributions and Bino-Higgsino Dark Matter at the LHC

Pair production of light top squarks at the 8-TeV LHC can be used to probe the gaugino-Higgsino sector of the Minimal Supersymmetric Standard Model. The case where the lightest neutralino is a mixture of Bino and Higgsino, satisfying the thermal dark matter relic density, is investigated. In such a scenario, the lightest top squark decays mostly into $(i)$ a top quark plus the second or third lightest neutralino, and $(ii)$ a bottom quark plus the lightest chargino, instead of a decay scenario of the lightest top squark into a top quark and the lightest neutralino. Final states with $\geq 2$ jets, dileptons, and missing energy are expected in a subsequent decay of the second or third lightest neutralinos into the lightest neutralino via an intermediate slepton ("light sleptons" case) or $Z$ boson ("heavy sleptons" case). The opposite-sign same flavor dilepton mass distribution after subtracting the opposite-sign different flavor distribution shows a clear edge in the case of light sleptons. The significance for discovering such a scenario is calculated with optimized cuts in both light and heavy sleptons cases.