  The results of a search with the DELPHI Barrel RICH for Cherenkov rings
having radii greater than those produced by ultrarelativistic particles are
presented. The search for such anomalous rings is based on the data collected
by the DELPHI Collaboration at CERN during the LEP1 and LEP2 periods. The
DELPHI RICH detector was conceived for the identification of the stable and
quasi-stable hadrons ($\pi/K/p$). The present analysis was made investigating
electron-like particles. A subsample of events containing anomalous rings has
been identified for which the probability that the reconstructed rings in a
given event are due to fortuitous combinations of background hits is low
($10^{-3}$ or less). A detailed study of background sources capable of
producing apparently anomalous rings has been done; it indicates that the
background hypothesis has a low probability. Additional arguments against this
hypothesis are provided by by a comparison of rates of events with single and
double anomalous rings in the gaseous radiator, and by the observation of a
high degree of correlation between anomalous ring radii in the liquid and
gaseous radiators. The results of the present analysis provide an interesting
indication of the existence of anomalous Cherenkov rings. To corroborate this
indication further searches for anomalous rings need to be made in future
dedicated experiments.
  This work has been performed by the authors following the rules for external
access to the DELPHI archived data, as established in
http://delphiwww.cern.ch/delsec/finalrules/FINALrules011203.pdf The opinions,
findings and conclusions expressed in this material are those of the authors
alone and do not reflect in any way the views of the DELPHI Collabora
