Search for Excited Muons in ppbar Collisions at sqrt(s) = 1.96 TeV
  We present the results of a search for the production of an excited state of the muon, mu*, in proton antiproton collisions at sqrt s = 1.96 TeV. The data have been collected with the D0 experiment at the Fermilab Tevatron Collider and correspond to an integrated luminosity of approximately 380 pb^-1. We search for mu* in the process p pbar -> mu* mu, with the mu* subsequently decaying to a muon plus photon. No excess above the standard model expectation is observed in data. Interpreting our data in the context of a model that describes mu* production by four-fermion contact interactions and mu* decay via electroweak processes, we exclude production cross sections higher than 0.057 pb -- 0.112 pb at the 95% confidence level, depending on the mass of the excited muon. Choosing the scale for contact interactions to be Lambda = 1 TeV, excited muon masses below 618 GeV are excluded. 
D0 Collaboration, V. Abazov, et al