Stop and sbottom search using dileptonic $M_{T2}$ variable and boosted top technique at the LHC

Amit Chakraborty, Dilip Kumar Ghosh, Diptimoy Ghosh, Dipan Sengupta

Published 2013-03-22, updated 2013-09-29Version 2

The ATLAS and CMS experiments at the CERN LHC have collected about 20 $fb^{-1}$ of data each at the end of their 8 TeV run, and ruled out a huge swath of parameter space in the context of Minimally Supersymmetric Standard Model(MSSM). Limits on masses of the gluino ($\tilde{g}$) and the squarks of the first two generations($\tilde{q}$) have been pushed to the TeV range. Light third generation squarks namely stop and sbottom of sub-TeV masses, on the other hand, are still allowed by their direct search limits. Interestingly, the discovery of a Standard Model(SM) higgs boson like particle with a mass of $\sim$ 125 GeV favours a light third generation which is also motivated by naturalness arguments. Decays of stop and sbottom quarks can in general produce a number of distinct final states which necessitate different search strategies in the collider experiments. In this paper we, on the other hand, propose a general search strategy to look for third generation squarks in the final state which contains a top quark in the sample along with two additional hard leptons and substantial missing transverse momentum. We illustrate that a search strategy using the dileptonic $M_{T2}$, the effective mass $m_{eff}$ and jet substructure to reconstruct the hadronic top quark can be very effective to reduce the SM backgrounds. With the proposed search strategy, we estimate that the third generation squarks with masses up to about 800 GeV can be probed at the 14 TeV LHC with a 100 $fb^{-1}$ data set. We also interpret our results in two simplified scenarios where we consider the stop (sbottom) pair production followed by their subsequent decay to a top quark and the second lightest neutralino (lightest chargino). In this case also we find that stop (sbottom) mass up to 1 TeV (0.9 TeV) can be discovered at the 14 TeV LHC with 100 $fb^{-1}$ integrated luminosity.