Abstract
A search for supersymmetry involving the pair production of gluinos decaying via third-generation squarks into the lightest neutralino left({tilde{chi}}_1^0right) is reported. It uses LHC proton-proton collision data at a centre-of-mass energy sqrt{s}=13 TeV with an integrated luminosity of 36.1 fb−1 collected with the ATLAS detector in 2015 and 2016. The search is performed in events containing large missing transverse momentum and several energetic jets, at least three of which must be identified as originating from b-quarks. To increase the sensitivity, the sample is divided into subsamples based on the presence or absence of electrons or muons. No excess is found above the predicted background. For {tilde{chi}}_1^0 masses below approximately 300 GeV, gluino masses of less than 1.97 (1.92) TeV are excluded at 95% confidence level in simplified models involving the pair production of gluinos that decay via top (bottom) squarks. An interpretation of the limits in terms of the branching ratios of the gluinos into third-generation squarks is also provided. These results improve upon the exclusion limits obtained with the 3.2 fb−1 of data collected in 2015.
Highlights
Lighter than the other squarks [12, 13]
For χ01 masses below approximately 300 GeV, gluino masses of less than 1.97 (1.92) TeV are excluded at 95% confidence level in simplified models involving the pair production of gluinos that decay via top squarks
This paper presents a search for pair-produced gluinos decaying via top or bottom squarks in events with multiple jets originating from the hadronisation of b-quarks (b-jets in the following), high missing transverse momentum of magnitude ETmiss, and potentially additional light-quark jets and/or an isolated charged lepton
Summary
Various simplified SUSY models [17, 18] are employed to optimise the event selection and/or interpret the results of the search. In the Gbb (Gtt) model, illustrated in figure 1(a) (1(b)), each gluino undergoes an effective three-body decay g → bbχ (g → ttχ01) via off-shell bottom (top) squarks, with a branching ratio of 100%. The Gbb model is the simplest in terms of particle multiplicity, resulting in the minimal common features of four b-jets and two χ01 In addition to these particles, the Gtt model produces four W bosons originating from the top quark decays:. The products of the decay W ∗ → f fare typically too soft to be detected, except for very large mass differences between the gluino and the χ±1 In this model, the gluino can decay as either g → bbχ, g → tbχ−1 (with χ−1 → f fχ ̃01) or g → ttχ, with the sum of individual branching ratios adding up to 100%.
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