Stop and sbottom search using dileptonic MT2 variable and boosted top technique at the LHC

Abstract

The ATLAS and CMS experiments at the CERN LHC have collected about 25 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 (g) and the squarks of the first two generations (q) have been pushed to above 1 TeV. 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 ∼ 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 900 GeV can be probed at the 14 TeV LHC with 100 fb −1 luminosity. 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.

Gluino mass limits with sbottom NLSP in coannihilation scenarios

“…A large number of phenomenological analyses have already addressed various topics/issues related to stop searches in different channels [27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42] and investigated DM production via t 1 -χ 0 1 coannihilation [37][38][39][40][41][42] extensively in the context of LHC. On the other hand the sbottom NLSP scenario, which also has the potential of explaining the observed relic density, has not yet received due attention and has been addressed by a relatively small number of analyses only [43][44][45][46][47][48][49][50][51]. Moreover, most of the analyses predating the first phase of the LHC experiments were restricted to mSUGRA motivated models with non-universal boundary conditions.…”

Jet substructures of boosted polarized top quarks

“…Note that the variablesx J b and cosθ J b are understood as functions of x J b and cos θ J b through Eq. (17). Moreover, we have replaced the bottom- (18).…”

“…Exploration of new physics beyond the standard model by means of boosted top quarks was studied intensively in [10][11][12][13][14][15][16][17][18][19][20]. Various strategies for tagging a boosted top quark were proposed in [21][22][23][24][25][26][27][28], and experimental searches have been conducted by the experiment ATLAS and CMS at the LHC recently [29,30].…”

Hadronic b′ search at the LHC with top and W taggers

“…Using the jet substructure techniques [42,43], it offers a promising method to pick out possible signals while keep good suppression to the SM multiple jet final states. Based on Monte Carlo methods, these jet substructure techniques have been demonstrated to work quite well in searching for top partners and bottom partners [44][45][46][47][48][49][50]. Recently, theoretical understanding on jet physics from QCD side has brought new insights to the jet substructure and related phenomenological analysis methods, such as jet functions [51], grooming [52], quark/gluon separation [53,54] etc.…”