A search for pair produced vector-like T quarks in dilepton and multi-jet final states at sqrt (s) = 13 TeV

The Standard Model fermions are known to be chiral in nature. Several new theories like composite Higgs models, Randall-Sundrum model, GUTs etc. however predict the existence of newheavy vector-like fermions. In this thesis, we explore the possibility of finding heavy vector-likepartners of the top quark, namely the Tprime (T) quark, in pp collisions at the LHC at a centreof mass energy of 13 TeV. We have assumed that the T decays to a top quark and a Z boson with100 % branching ratio (T→tZ). We look for pair produced T quarks decaying to a dilepton and amulti-jet final state.The T quark, if found in nature, is expected to be very massive. Its decay products will, therefore,have a considerable boost. We have used the properties of boosted decay topologies in designinga χ2 algorithm that chooses the best possible candidates for the decay products of the T quark inan event. Using candidates selected by the χ2 algorithm, we reconstruct an invariant mass for theT quark.We set expected and observed 95% CL upper limits on the TT production cross-sectionusing the Asymptotic CLs method. We were able to set an expected 95 % CL lower limit of 1170GeV on the T quark mass. We also used the χ2 algorithm on the data (integrated luminosity of35.9 fb−1 ) and were able to exclude T quark masses below 1095 GeV with 95% CL.1