High-precision measurement of $\Gamma(Z \to b\overline{b}) / \Gamma(Z \to hadrons)$ with the DELPHI detector at LEP collider

[...] where the first error is statistical and the second one systematic. The explicit dependence with the assumed value of $R_c$ is also given. This number is still preliminary. Within a 0.53\% relative precision, the result is in good agreement with the current Standard Model expectation, $R_b^0=0.2158\pm0.0003$, as predicted for a top quark mass of $175.6\pm 5.5$ GeV/$c^2$ as measured at FNAL. If the radiative corrections (dominated by top quark effects) were left out of the electroweak calculation, the expected result would be $R_b^0=0.2183\pm0.0001$. Therefore, this measurement shows evidences that the $Z \rightarrow b\bar{b}$ vertex is dominated by radiative corrections due to the top quark. This experimental result is consistent with other precise determinations performed at LEP/SLC colliders, but it is the more precise one.