Multijet studies in DELPHI

The effect of the heavy b-quark mass is studied measuring the normalized n-jet rates of b-quarks with respect to light-quarks (l = uds), R/sub n//sup bl/ (n=2-5), using the Cambridge jet clustering algorithm with LEP data collected by the Delphi experiment at the Z peak. Results are compared with generators (at hadron level) and massive LO calculations. R/sub 3//sup bl/ is used to extract values for the b-quark mass at the M/sub Z/ energy scale defined in the MS scheme, m/sub b/(M/sub Z/) and to test alpha /sub s/ 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.