Özet:
This thesis searches for the heavy iso-singlet quarks forseen by F. Gursey, P. Ramond and P. Sikivie' s E6 grand uni ed theory model using the data recorded by the ATLAS detector under the pp ! DD ! HjZj ! 4j 2l decay hypothesis. (a avor changing neutral current process). The data used in the analysis corresponds to 20 fb{u100000}1 total integrated luminosity collected from proton proton collision at c.o.m. energy of 8TeV, provided by the large hadron collider The analysis uses a cut based algorithm to select the events with four jets and a Z candidate that has been reconstructed from two charged leptons. Flavor tagging is used to improve the reconstruction of the Higgs bosons. No excess events beyond what is predicted by the Standard Model has been observed and the E6 heavy iso-singlet quark with a mass lower then 490 GeV is excluded at 95% con dence level. Also no excess events beyond what is predicted by the Standard Model has been observed on the search for a heavy quark that decays only via avor changing neutral currents. For this quark, the mass lower then 730 GeV is excluded with the 95% con dence level.
