SEARCH FOR MUON TO ELECTRON NEUTRINO OSCILLATIONS

A search for upsilon(mu) --> upsilon(e) and ($) over bar upsilon(mu) --> ($) over bar upsilon(e) oscillations has been carried out with the CHARM LI detector exposed to the CERN wide band neutrino beam. The data were collected over five years, alternating beams mainly composed of muon-neutrinos and muon-antineutrinos. The number of interactions of upsilon(e) and ($) over bar upsilon(e) observed is comparable with the number of events expected from flux calculations. For large squared mass differences the upper limits obtained on the mixing angle are sin(2)2 theta < 9.4.10(-3) for upsilon(mu) oscillating to upsilon(e) and sin(2)2 theta < 4.8.10(-3) for ($) over bar upsilon(mu) to ($) over bar upsilon(e) at the 90% confidence level. Combining neutrino and antineutrino data the upper limit is 5.6.10(-3).