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We perform a detailed study of top-quark partner production in the ttbar pluslarge missing energy final-state at the LHC, presenting results for both scalarand fermionic top-quark partners in the semi-leptonic and dileptonic decaymodes of the top quarks. We compare the results of several simulation tools:leading-order matrix elements, next-to-leading order matrix elements,leading-order plus parton shower simulations, and merged samples that containthe signal process with an additional hard jet radiated. We find thatpredictions from leading-order plus parton shower simulations can significantlydeviate from NLO QCD or LO merged samples and do not correctly model thekinematics of the ttbar + ETmiss signature. They are therefore not a goodframework for modeling this new physics signature. On the other hand, theacceptances obtained with a merged sample of the leading-order process togetherwith the radiation of an additional hard jet are in agreement with the NLOpredictions. We also demonstrate that the scale variation of the inclusivecross section, plus that of the acceptance, does not accurately reflect theuncertainty of the cross section after cuts, which is typically larger. We showthe importance of including higher-order QCD corrections when using kinematicdistributions to determine the spin of the top-quark partner.

ttbar+Large missing energy from top-quark partners: a comprehensive study at NLO QCD