Mass of the b-quark at LEP

The effect of the heavy b-quark mass is studied measuring the normalized n-jet rates of bquarks with respect to light-quarks (e = uds), R!:,.1 (n=2-4), using the CAMBRIDGE jet clustering algorithm with LEP data collected by the Delphi exper;ment at the Z peak .. Results are compared with generators (at hadron level) and massive NLO calculations. R�1 is used to extract values for the b-quark mass at the Mz energy scale defined in the MS scheme, mb(Mz) and to test a, universality. The validity of approximating massive NLO corrections by their corresponding massless ones is investigated with the aim to measure the b-quark mass in four-jet events