Search for Excited Quarks in $q\bar{q} \to γγ$ at the LHC

If quarks are composite particles, then excited states are expected to play a r\^ole in the Large Hadron Collider phenomena. Concentrating on virtual effects, and using a large part of the CMS detection criteria, we present here a realistic examination of their effect in diphoton production at the LHC. For various luminosities, we present the 99 % confidence limit (CL) achievable in $\Lambda-M_{q*}$ parameter space where $\Lambda$ is the compositeness scale and M_{q^*} the mass of the state. For a q^* of mass 0.5 TeV, $\Lambda \leq 1.55 (2.95)$ can be excluded at 99% CL with 30 (200)${\rm fb}^{-1}$ integrated luminosity.