We acknowledge in particular the support of Austrian Federal Ministry of Science and Tracs, GZ 616.364/2-III/2a/98, FNRS-FWO, Belgium, FINEP, CNPq, CAPES, FUJB and FAPERJ, Brazil, Czech Ministry of Industry and Trade, GA CR 202/96/0450 and GA AVCR A1010521, Danish Natural Research Council, Commission of the European Communities (DG XII), Direction des Sciences de la Matiere, CEA, France, Bundesministerium fur Bildung, Wissenschaft, Forschung und Technologie, Germany, General Secretariat for Research and Technology, Greece, National Science Foundation (NWO) and Foundation for Research on Matter (FOM), The Netherlands, Norwegian Research Council, State Committee for Scientific Research, Poland, 2P03B06015, 2P03B03311 and SPUB/P03/178/98, JNICT-Junta Nacional de Investigaçao Cientifica e Tecnologica, Portugal, Vedecka grantova agentura MS SR, Slovakia, Nr. 95/5195/134, Ministry of Science and Technology of the Republic of Slovenia, CICYT, Spain, AEN96{1661 and AEN96-1681, The Swedish Natural Science Research Council, Particle Physics and Astronomy Research Council, UK, Department of Energy, USA, D-FG02-94ER40817.

The partial decay width of the Z to bb̄ quark pairs has been measured by the DELPHI detector at LEP using data taken in the years 1992 to 1995. Decays of b-hadrons were tagged by several methods using tracks with large impact parameters and/or reconstructed secondary vertices, complemented by event shape variables. Combining these methods in a multivariate analysis the value Γ(Z → bb̄)/Γ(Z → had) = 0.21634 ± 0.00067 (stat) ± 0.00060 (syst) was obtained, where the cc̄ production fraction was fixed to its Standard Model value.

DELPHI Collaboration: et al.

CERN-EP/98-180

Peer reviewed