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 --> b (b) over bar b (b) over bar was measured using about 2 x 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-4b = BR(Z --> b (b) over bar b (b) over bar/BR(Z --> hadrons), = (6.0 +/- 1.9(stat.) +/- 1.4(syst.)) x 10(-4) where the invariant mass of every b (b) over bar system is above twice the b quark mass. Using the value of R-4b the probability of secondary production of a b (b) over bar 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.)) x 10(-3). (C) 1999 Published by Elsevier Science B.V. All rights reserved. RI De Angelis, Alessandro/B-5372-2009; Gonzalez Caballero, Isidro/E-7354-2010; Krammer, Manfred/A-6508-2010; Muresan, Raluca-Anca/C-3725-2011; Katsanevas, Stavros/A-4297-2011; Ruiz, Alberto/E-4473-2011; Marti-Garcia, Salvador/F-3085-2011; Verzi, Valerio/B-1149-2012; branchini, paolo/A-4857-2011; Shellard, Ronald/G-4825-2012; Monge, Maria Roberta/G-9127-2012; Petrolini, Alessandro/H-3782-2011; Fruhwirth, Rudolf/H-2529-2012