Abstract
A search for direct pair production of top squarks in final states with two tau leptons, $b$-jets, and missing transverse momentum is presented. The analysis is based on proton-proton collision data at $\sqrt{s} = 13$ TeV corresponding to an integrated luminosity of 36.1 fb$^{-1}$ recorded with the ATLAS detector at the Large Hadron Collider in 2015 and 2016. Two exclusive channels with either two hadronically decaying tau leptons or one hadronically and one leptonically decaying tau lepton are considered. No significant deviation from the Standard Model predictions is observed in the data. The analysis results are interpreted in terms of model-independent limits and used to derive exclusion limits on the masses of the top squark $\tilde t_1$ and the tau slepton $\tilde \tau_1$ in a simplified model of supersymmetry with a nearly massless gravitino. In this model, masses up to $m(\tilde t_1) = 1.16$ TeV and $m(\tilde \tau_1) = 1.00$ TeV are excluded at 95% confidence level.
Highlights
Supersymmetry (SUSY) [1,2,3,4,5,6] extends the Standard Model (SM) with an additional symmetry that connects bosons and fermions, thereby providing answers to several of the open questions in the SM
In the model considered in this work, the conservation of R-parity is assumed [8], so that the supersymmetric particles are produced in pairs, and the lightest supersymmetric particle (LSP) is stable, providing a viable candidate for dark matter
Signal samples were generated from leading-order (LO) matrix elements (ME) with MADGRAPH5_aMC@next-toleading order (NLO) v2.2.3 and v2.3.3 [32] interfaced to PYTHIA 8.186, 8.205 or 8.210 [33,34] with the ATLAS 2014 (A14) [35] set of tuned parameters for the modeling of the parton showering (PS), hadronization and underlying event
Summary
Supersymmetry (SUSY) [1,2,3,4,5,6] (see Ref. [7] for a review) extends the Standard Model (SM) with an additional symmetry that connects bosons and fermions, thereby providing answers to several of the open questions in the SM. [7] for a review) extends the Standard Model (SM) with an additional symmetry that connects bosons and fermions, thereby providing answers to several of the open questions in the SM It predicts the existence of new particles that have the same mass and quantum numbers as their SM partners but differ in spin by one half-unit. A previous analysis considering the same three-body decay mode of the top squark ptoffiffi the tau slepton based on 20 fb−1 of ATLAS data at s 1⁄4 8 TeV set lower limits on the mass of the top squarkt of up to 650 GeV [22]. The “lep-had” channel refers to events in which one of the tau leptons decays leptonically and the other hadronically Final states where both tau leptons decay leptonically have the smallest branching ratio and are not considered, as studies showed that they would not contribute significantly to the sensitivity of the analysis.
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