We searched for third-generation squarks in fully hadronic final states and presented them using data samples corresponding to integrated luminosities of 19.4 or 19.7 fb-1, collected at a centre-of-mass energy of 8 TeV with the CMS detector at the LHC. Three mutually exclusive searches are presented, each optimized for a different decay topology. They include a multijet search requiring one fully reconstructed top quark, a dijet search requiring one or two jets originating from b quarks, and a monojet search. Furthermore, no excesses above the standard model expectations are seen, and limits are set on top and bottom squark production in the context of simplified models of supersymmetry.

Searches for third-generation squarks in fully hadronic final states are presented using data samples corresponding to integrated luminosities of 19.4 or 19.7 fb−1, collected at a centre-of-mass energy of 8 TeV with the CMS detector at the LHC. Three mutually exclusive searches are presented, each optimized for a different decay topology. They include a multijet search requiring one fully reconstructed top quark, a dijet search requiring one or two jets originating from b quarks, and a monojet search. No excesses above the standard model expectations are seen, and limits are set on top and bottom squark production in the context of simplified models of supersymmetry.

Searches are presented for direct production of top or bottom squark pairs in proton-proton collisions at the CERN LHC. Two searches, based on complementary techniques, are performed in all-jet final states that are characterized by a significant imbalance in transverse momentum. An additional search requires the presence of a charged lepton isolated from other activity in the event. The data were collected in 2015 at a centre-of-mass energy of 13 TeV with the CMS detector and correspond to an integrated luminosity of 2.3 inverse femtobarns. No statistically significant excess of events is found beyond the expected contribution from standard model processes. Exclusion limits are set in the context of simplified models of top or bottom squark pair production. Models with top and bottom squark masses up to 830 and 890 GeV, respectively, are probed for light neutralinos. For models with top squark masses of 675 GeV, neutralino masses up to 260 GeV are excluded at 95% confidence level.

Three searches for third generation squarks using proton-proton collision data at a center-of-mass energy of 13 TeV recorded by the CMS experiment at the LHC are presented. The data corre- spond to an integrated luminosity of 12.9 fb-1. The analyses define exclusive search regions and estimate contributions from standard model processes to these regions by using control samples in the data. No significant deviation from the standard model expectation is observed in the data. The results are interpreted in simplified SUSY models of direct and gluino-mediated top squark production. Depending on the model, top squark masses up to 910 GeV and gluino masses up to 1780 GeV are excluded.

A search for pair production of third-generation scalar leptoquarks and supersymmetric top quark partners, top squarks, in final states involving tau leptons and bottom quarks is presented. The search uses events from a data sample of proton-proton collisions corresponding to an integrated luminosity of 19.7 fb-1, collected with the CMS detector at the LHC with [arrow]" = 8 TeV. The number of observed events is found to be in agreement with the expected standard model background. Third-generation scalar leptoquarks with masses below 740 GeV are excluded at 95% confidence level, assuming a 100% branching fraction for the leptoquark decay to a tau lepton and a bottom quark. In addition, this mass limit applies directly to top squarks decaying via an R-parity violating coupling [lambda]'333. The search also considers a similar signature from top squarks undergoing a chargino-mediated decay involving the R-parity violating coupling [lambda]'3jk. Each top squark decays to a tau lepton, a bottom quark, and two light quarks. Top squarks in this model with masses below 580 GeV are excluded at 95% confidence level. The constraint on the leptoquark mass is the most stringent to date, and this is the first search for top squarks decaying via [lambda]'3jk.

Abstract: Supersymmetry poses one of the best motivated theories for particle physics beyond the Standard Model. It can provide a dark matter candidate and enable grand unification. The supersymmetric partner of the top quark, the top squark, can provide a cancellation of diverging radiative corrections to the Higgs-boson mass and thereby avoid the hierarchy problem of the Standard Model. In this thesis, a search for top squarks in final states with jets and missing transverse momentum is presented. Proton-proton collisions at a centre-of-mass energy of √s = 13 TeV, produced by the Large Hadron Collider, were recorded by the ATLAS detector. The analysed dataset corresponds to an integrated luminosity of 36.1 fb-1. No significant excess above the Standard Model background was observed. The analysis results are interpreted as exclusion limits on the top-squark mass and the neutralino mass in various scenarios that address specific aspects of the supersymmetry

A search for the production of heavy resonances decaying into top quark-antiquark pairs is presented. The analysis is performed in the lepton+jets and fully hadronic channels using data collected in proton-proton collisions at $\sqrt{s}$ =13 TeV using the CMS detector at the LHC, corresponding to an integrated luminosity of 2.6 inverse femtobarns. The selection is optimized for massive resonances, where the top quarks have large Lorentz boosts. No evidence for resonant ttbar production is found in the data, and upper limits on the production cross section of heavy resonances are set. The exclusion limits for resonances with masses above 2 TeV are significantly improved compared to those of previous analyses at $\sqrt{s}$ = 8 TeV.