Production rates of $\mathrm{b\overline{b}}$ quark pairs from gluons and $\mathrm{b\overline{b}b\overline{b}}$ events in hadronic $\mathrm{Z}^0$ decays

Abstract.

The rates are measured per hadronic $\mathrm{Z}^0$ decay for gluon splitting to $\mathrm{b\overline{b}}$ quark pairs, $g_{\mathrm{b\overline{b}}}$, and of events containing two $\mathrm{b\overline{b}}$ quark pairs, $g_{\mathrm{4b}}$, using a sample of four-jet events selected from data collected with the OPAL detector. Events with an enhanced signal of gluon splitting to $\mathrm{b\overline{b}}$ quarks are selected if two of the jets are close in phase-space and contain detached secondary vertices. For the event sample containing two $\mathrm{b\overline{b}}$ quark pairs, three of the four jets are required to have a significantly detached secondary vertex. Information from the event topology is combined in a likelihood fit to extract the values of $g_{\mathrm{b\overline{b}}}$ and $g_{\mathrm{4b}}$, namely

\begin{eqnarray*} g_{\mathrm{b\overline{b}}} & = & (3.07 \pm 0.53 \mathrm{(stat)} \pm 0.97\mathrm{(syst)})\times 10^{-3},\\ g_{\mathrm{4b}} & = & (0.36\pm 0.17 \mathrm{(stat)} \pm 0.27\mathrm{(syst)})\times 10^{-3}. \end{eqnarray*}