A measurement ofΓ (Z0→b/Γ(Z0→hadrons) using an impact parameter technique

The fractional partial width of theZ0 tob quarks,$$\Gamma _{b\bar b} /\Gamma _{had} $$, has been measured by OPAL using an impact parameter technique. The method has been developed using 130 000 hadronic events collected by OPAL in 1990. We find:$$\frac{{\Gamma _{b\bar b} }}{{\Gamma _{had} }} = 0.222 \pm 0.007(stat) \pm 0.008(sys).$$ The measurement assumes the relative rates of theZ0 touds andc quarks given by the Standard Model. Varying the charm fraction from the Standard Model value of$$\Gamma _{c\bar c} /\Gamma _{had} = 0.171$$ changes the result by an additional$$\Delta \Gamma _{b\bar b} /\Gamma _{b\bar b} = - 0.135 \times \Delta \Gamma _{c\bar c} /\Gamma _{c\bar c} $$.