Quark excitations through the prism of direct photon plus jet at the LHC

Abstract

The quest to know the structure of matter has resulted in various theoretical speculations wherein additional colored fermions are postulated. Arising either as Kaluza-Klein excitations of ordinary quarks, or as excited states in scenarios wherein the quarks themselves are composites, or even in theories with extended gauge symmetry, the presence of such fermions (q*) can potentially be manifested in γ+jet final states at the LHC. Using unitarized amplitudes and the CMS setup, we demonstrate that in the initial phase of LHC operation (with an integrated luminosity of 200 pb⁻¹) one can discover such states for a mass up to 2.0 TeV. The discovery of a q* with a mass as large as ~5 TeV can be achieved for an integrated luminosity of ~140 fb⁻¹. We also comment on the feasibility of mass determination.