Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany II. Institut f. Experimentalphysik, Universität Hamburg, Germany Physikalisches Institut der Universität Heidelberg, Germany University of lancaster, England University of Manchester, England Rutherford Appleton Laboratory, Chilton, England a Lab. of Int. Coll. on Elementary Particle Physics, University of Tokyo, Japan b Department of Physics, University of Tokyo, Japan |