Article révisé par les pairs
Résumé : A search for supersymmetry through the direct pair production of top squarks, with Higgs (H) or Z bosons in the decay chain, is performed using a data sample of proton-proton collisions at s=8 TeV collected in 2012 with the CMS detector at the LHC. The sample corresponds to an integrated luminosity of 19.5 fb-1. The search is performed using a selection of events containing leptons and bottom-quark jets. No evidence for a significant excess of events over the standard model background prediction is observed. The results are interpreted in the context of simplified supersymmetric models with pair production of a heavier top-squark mass eigenstate t~2 decaying to a lighter top-squark mass eigenstate t~1 via either t~2→Ht~1 or t~2→Zt~1, followed in both cases by t~1→tχ~10, where χ~10 is an undetected, stable, lightest supersymmetric particle. The interpretation is performed in the region where the mass difference between the t~1 and χ~10 states is approximately equal to the top-quark mass (mt~1-mχ~10≃mt), which is not probed by searches for direct t~1 squark pair production. The analysis excludes top squarks with masses mt~2<575 GeV and mt~1<400 GeV at a 95% confidence level.

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