Search for pair production of excited top quarks in the lepton+jets final state

A search is performed for pair production of spin-3/2 excited top quarks, each decaying to a top quark and a gluon. The search uses the data collected with the CMS detector from pp collisions at a center-of-mass energy of $\sqrt{s}=13\,\textrm{TeV}$, corresponding to an integrated luminosity of 36$\,\textrm{fb}^{-1}$. The selected events require the presence of an isolated muon or electron, an imbalance in the transverse momentum, and at least six jets, out of which exactly two must be compatible with originating from the fragmentation of a b quark. The analysis shows no significant excess over the standard model predictions, and provides a lower limit of $1.2\,\textrm{TeV}$ at $95\%$ confidence level on the mass of the spin-3/2 excited top quark in an extension of the Randall--Sundrum model, assuming a $100\%$ branching fraction of its decay into a top quark and a gluon.