1. Blackett Laboratory, Imperial College London, SW7 2AZ, UK.
2. CESR, 31028 Toulouse, France.
3. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA.
4. Department of Physics and Astronomy, Leicester University, Leicester, LE1 7RH, UK.
5. KFKI Research Institute for Particle and Nuclear Physics, H-1525 Budapest, Hungary.