A measurement ofΓ (Z 0→b $$\Gamma ({\rm Z}^0 \to b\bar b)$$ /Γ(Z 0→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\(\Delta \Gamma _{b\bar b} /\Gamma _{b\bar b} = - 0.135 \times \Delta \Gamma _{c\bar c} /\Gamma _{c\bar c} \).