Search for Anomalous Production of Acoplanar Di-lepton Events in e+e-          
collisions at sqrt(s) = 183 and 189 GeV                                        
  
A selection of di-lepton events with significant missing transverse momentum   
has been performed using a total data sample of 237.4 inverse pico-barns       
at e+e- centre-of-mass energies of 183 GeV and 189 GeV.                        
The observed numbers of events --- 78 at 183 GeV and 301 at 189 GeV  ---       
are consistent with the numbers expected from Standard Model processes,        
which arise predominantly from W-pair production with each W decaying          
leptonically.                                                                  
This topology is also an experimental                                          
signature for the pair production of new particles that decay                  
to a charged lepton accompanied by one or more                                 
invisible particles.                                                           
Discrimination techniques are described that optimise                          
the sensitivity to particular new physics channels.                            
No evidence for new phenomena is apparent and model independent limits         
are presented on the production cross-section times branching ratio squared    
for sleptons and for leptonically decaying charginos and charged Higgs.        
  
 Parallel session :11                  
 Plenary  session :7a