Measurement of the rate of bbbb events in hadronic Z decays and the extraction of the gluon splitting into bb

Abstract The rate Z → b b b b was measured using about 2×10 6 hadronic decays collected by the DELPHI experiment in 1994 and 1995. Events were forced into 3-jets with y min >0.06 and a b-tag was required for every jet. The rate was measured to be: R 4 b = BR ( Z → b b b b ) BR ( Z →hadrons) =(6.0±1.9 (stat.) ±1.4 (syst.) )×10 −4 where the invariant mass of every b b system is above twice the b quark mass. Using the value of R 4b the probability of secondary production of a b b pair from a gluon per hadronic Z decay, g bb , was extracted and found to be: g bb =(3.3±1.0(stat.)±0.8(syst.))×10 −3 .