Measurement of the Rate of bb-barbb-bar events in Hadronic Z Decays in DELPHI and the extraction of the gluon splitting into bb-bar

Z → bb-barbb-bar was measured using about 2 x 106 hadronic decays collected by the DELPHI experiment in 1994 and 1995. The analysis was performed forcing events to a 3-jet topology with ymin > 0.06 and requiring every jet to pass the b-tagging selection. The rate was measured to be: R4b = BR(Z → bb-barb-bar)/BR(Z → hadrons) = (5.4 ± 1.8(stat.) ± 1.5(syst.)) x 10-4 where the minimum invariant mass of every b-bar system is 2 · mb in the simulation. Using the value of R4b the rate of gluon splitting to bb-bar can be extracted and is found to be: gbb = (3.0 ± 1.0(stat.) ± 0.8(syst.)) x 10-3