Search for direct top squark pair production in events with a Higgs or $Z$ boson, and missing transverse momentum in $\sqrt{s}=13$ TeV $pp$ collisions with the ATLAS detector

Abstract

A search for direct top squark pair production resulting in events with either a same-flavour opposite-sign dilepton pair with invariant mass compatible with a $Z$ boson or a pair of jets compatible with a Standard Model (SM) Higgs boson ($h$) is presented. Requirements on additional leptons, jets, jets identified as originating from $b$-quarks, and missing transverse momentum are imposed to target the other decay products of the top squark pair. The analysis is performed using proton-proton collision data at $\sqrt{s}=13$ TeV collected with the ATLAS detector at the LHC in 2015--2016, corresponding to an integrated luminosity of 36.1 fb${}^{-1}$. No excess is observed in the data with respect to the SM predictions. The results are interpreted in two sets of models. In the first set, direct production of pairs of lighter top squarks (${\tilde{t}}_1$) with long decay chains involving $Z$ or Higgs bosons is considered. The second set includes direct pair production of the heavier top squark pairs (${\tilde{t}}_2$) decaying via ${\tilde{t}}_2\to Z{\tilde{t}}_1$ or ${\tilde{t}}_2\to h{\tilde{t}}_1$. The results exclude at 95\% confidence level ${\tilde{t}}_2$ and ${\tilde{t}}_1$ masses up to about 800 GeV, extending the exclusion region of supersymmetric parameter space covered by previous LHC searches.

29 pages plus author list + cover pages (46 pages total), 7 figures, 9 tables, submitted to JHEP, All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/SUSY-2016-20/

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Cited by in corpus (3)

• Search for direct production of supersymmetric partners of the top quark in the all-jets final state in proton-proton collisions at sqrt(s) = 13 TeV
• Global aspects of the renormalization group and the Hierarchy problem
• Production of a light top-squark pair in association with a light non-standard Higgs boson within the NMSSM at the 13 TeV LHC and a 33 TeV proton collider