Single and Pair Production of Excited Top Quarks in Hadronic Collisions at \({\sqrt{s}=13}\) and \({14}\) TeV

Abstract

We explore the collider phenomenology of spin-\(1/2\) excited top quarks arising from QCD-invariant magnetic transition operators, motivated by scenarios in which Standard Model fermions are composite objects. Assuming the absence of electroweak and contact interactions, we consider a minimal effective field theory framework where the excited top decays exclusively via the strong channel \(t^{*}\to tg\). Both pair and single excited top production are studied at proton–proton colliders with center-of-mass energies \(\sqrt{s}=13\) and \(14\) TeV, corresponding to the LHC and HL-LHC regimes. We compute the total cross sections for both production modes, including all gauge and magnetic contributions, and examine their dependence on the compositeness scale \(\Lambda\) and excited top mass \(m_{t^{*}}\). While pair production proceeds primarily through minimal QCD couplings and exhibits limited sensitivity to \(\Lambda\), single production is governed by the magnetic transition operator and provides a complementary probe with distinct kinematic features. Our results highlight the dominant role of single production across a wide region of parameter space, particularly in the natural scenario \(\Lambda=m_{t^{*}}\), underscoring its relevance for future searches targeting excited top signatures with boosted topologies.