Measurement of the rate of b(b)over-bar-b(b)over-bar events in hadronic Z decays and the extraction of the gluon splitting into b(b)over-bar

The rate Z → bbbb was measured using about 2×106 hadronic decays collected by the DELPHI experiment in 1994 and 1995. Events were forced into 3-jets with ymin > 0.06 and a b-tag was required for every jet. The rate was measured to be: R4b = BR(Z → bbbb)/BR(Z → hadrons), = (6.0 ± 1.9(stst.)) ± 1.4(Syst.)) × 10-4 where the invariant mass of every bb system is above twice the b quark mass. Using the value of R4b the probability of secondary production of a bb pair from a gluon per hadronic Z decay, gbb, was extracted and found to be: gbb = (3.3 ± 1.0(stat) ± 0.8(syst.)) × 10-3. © 1999 Published by Elsevier Science B.V. All rights reserved.