Search for Excited Neutrinos from Z0 Decays

Physics Letters B, 1996

The production of nal states involving one or more energetic photons from e + e collisions at high energies is studied using data collected by the ALEPH detector at LEP. The data consist of two samples of 2:9 p b 1 each, recorded at centre-of-mass energies of 130 GeV and 136 GeV. The data are in agreement with the predictions of the Standard Model. From an analysis of two-photon nal states new limits are placed on the parameters of models involving e + e contact interactions and excited electrons. The 95% condence level lower limits on the QED cut-o parameters + and are found to be 169 and 132 GeV respectively.

Physical Review D, 2007

If quarks are composite particles, then excited states are expected to play a rôle 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 Λ − Mq * parameter space where Λ is the compositeness scale and Mq * the mass of the state. For a q * of mass 0.5 TeV, Λ ≤ 1.55 (2.95) can be excluded at 99% CL with 30 (200)fb −1 integrated luminosity.