Abstract
Naturalness arguments for weak-scale supersymmetry favour supersymmetric partners of the third generation quarks with masses not too far from those of their Stan- dard Model counterparts. Top or bottom scalar quarks (or squarks) with masses less than a few hundred GeV can give rise to direct pair production rates at the LHC that can be ob- served in the data sample recorded by the ATLAS detector. This proceeding summarises the latest results of a search for top squark pair production in final states with one isolated lepton, jets, and missing transverse momentum in √ s = 8 TeV pp collisions at the LHC, using 20. 7f b −1 of ATLAS data. Two top squark (˜) decay scenarios are considered: the decay to a top quark and a stable undetected neutral particle ( ˜ χ 0 ), and the decay to a bot- tom quark and a chargino, where the chargino decays via an on- or off-shell W boson to the ˜ χ 0 . The data are found to be consistent with Standard Model expectations and have been reinterpreted in terms of various SUSY scenarios.
Highlights
Supersymmetry (SUSY,[1,2,3,4,5,6,7,8,9]) is a theory that provides an extension of the Standard Model (SM) by adding a full set of new particles
In order to minimise the Monte Carlo (MC) dependence on the ETmiss modelling, the ttand W+jets backgrounds are separately normalised in each ETmiss slice
All systematics considered in this analysis are treated as nuisance parameters with Gaussian shapes in a fit based on the profile likelihood method
Summary
Supersymmetry (SUSY,[1,2,3,4,5,6,7,8,9]) is a theory that provides an extension of the Standard Model (SM) by adding a full set of new particles. The stop is needed to cancel the diverging loop contributions to the Higgs mass coming from SM top quarks, provided that the tmass is below the TeV range. These naturalness motivations and the wide range of exclusion limits obtained in the last years by the LHC experiments on SUSY searches favor a spectrum of SUSY particles that involve relatively light t (and b ) and heavy u, d, s, c. The interpretation of the results is performed in terms of simplified models, where particles’ unknown masses are free parameters and each decay is assumed to have 100% Branching Ratio (BR)
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