Measurement of the\(\Gamma _{b\bar b} /\Gamma _{had} \) branching ratio of thez by double hemisphere tagging

Two measurements of\(\Gamma _{b\bar b} /\Gamma _{had} \) are presented. Both measurements use 250000Z decays taken with the DELPHIdetector in 1991 and rely mainly on the precision of the microvertex detector. One tagging method is as simple as possible so that background rates can be reliably predicted by simulation. The other one uses a more involved tagging technique and reduces the dependence on simulation as much as possible. Combining both results,\(\Gamma _{b\bar b} /\Gamma _{had} \) is found to be 0.2209±0.0041(stat.)±0.0042(syst.)±0.0018\(\Gamma _{c\bar c} \).