Abstract
Results are reported from a search for the top squark, the lighter of the two supersymmetric partners of the top quark. The data sample corresponds to 19.7 inverse femtobarns of proton-proton collisions at sqrt(s) = 8 TeV collected with the CMS detector at the LHC. The search targets top squark to b chi+/- and top squark to t(*) chi0 decay modes, where chi+/- and chi0 are the lightest chargino and neutralino, respectively. The reconstructed final state consists of jets, b jets, missing transverse energy, and either one or two leptons. Leading backgrounds are determined from data. No significant excess in data is observed above the expectation from standard model processes. The results exclude a region of the two-dimensional plane of possible top squark and chi0 masses. The highest excluded top squark and chi0 masses are about 700 GeV and 250 GeV, respectively.
Highlights
Theories of supersymmetry (SUSY) predict the existence of a scalar partner for each standard model (SM) left-handed and right-handed fermion
Trajectories of charged particles are measured by a silicon pixel and strip tracker, covering 0 < φ < 2π in azimuth and |η| < 2.5, where the pseudorapidity η is defined as η = − ln[tan(θ/2)]; θ is the polar angle of the trajectory of the particle with respect to the counterclockwise beam direction
We study the impact of limited simulation statistics, generator scale variations, and jet energy scale (JES) uncertainty in the template fit method in the control region with zero b jets and no boosted decision tree (BDT) selection
Summary
Theories of supersymmetry (SUSY) predict the existence of a scalar partner for each standard model (SM) left-handed and right-handed fermion. When the symmetry is broken, the scalar partners acquire a mass different from their SM counterparts, the mass splitting between scalar mass eigenstates being dependent on the mass of the SM fermion. Because of the large mass of the top quark, the splitting between its chiral supersymmetric partners is potentially the largest among all supersymmetric quarks (squarks). As a result the lighter supersymmetric scalar partner of the top quark, the top squark ( t1), could be the lightest squark. SUSY scenarios with a neutralino (χ01) as lightest supersymmetric particle (LSP) and a nearly degenerate-mass t1 provide one theoretically possible way to produce the observed relic abundance of dark matter [4, 5]; this further motivates the search for the t1 at the LHC
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