V. Vrba, I. Ulb-vub, I. Pleinlaan, N. C. Fr-75231, P. O. Demokritos et al., IT-40126 Bologna, Italy 6 Centro Brasileiro de Pesquisas F sicas GR-15310 Athens, Greece 12 Dipartimento di Fisica, Universit a di Genova and INFN, Via Dodecaneso 33, IT-16146 Genova, Italy 13 Institut des Sciences Nucl eaires, IN2P3-CNRS, Universit e de Grenoble 1, FR-38026 Grenoble Cedex, France 14 Helsinki Institute of Physics, HIP, P .O. Box 9, FI-00014 Helsinki, Finland 15 Joint Institute for Nuclear Research RU-101 000 Moscow, Russian Federation 16 Institut f ur Experimentelle Kernphysik DE-76128 Karlsruhe, Germany 17 Institute of Nuclear Physics,Ul. Kawiory 26a, PL-30055 Krakow, Poland 18 Faculty o f P h ysics and Nuclear Techniques, University of Mining and Metallurgy, PL-30055 Krakow 24 Department o f P h ysics-1009 DB Amsterdam, The Netherlands 30 National Technical University, P h ysics Department, Zografou Campus, GR-15773 Athens, Greece 31 Physics Department a d i P adova and INFN, Via Marzolo 8, IT-35131 Padua a d i T rieste and INFN, Via A, Ph.Zoller 9 , M.Zupan 11 1 Department o f P h ysics and Astronomy Switzerland 9 Institut de Recherches Subatomiques, IN2P3 -CNRSSULP -BP20, FR-67037 Strasbourg Cedex, France 10 Now at DESY-Zeuthen, Platanenallee 6, D-15735 Zeuthen, Germany 11 Institute of Nuclear Physics FR-91405 Orsay Cedex SS olvegatan 14, SE-223 63 Ilha do Fund~ ao BR-21945-970 Rio de Janeiro AT-1050 Vienna, Austria 49 Inst. Nuclear Studies and University o f W arsaw References 11 B. Andersson, G. Gustafson, G. Ingelman, T. Sjj ostrand, Phys. Rep. 97 1983 31. T. Sjj ostrand and M. Bengtsson, Comp. Phys. Comm. 43, pp.50011-3160, 1987.