| Summary: | The effect of the heavy b-quark mass on the two, three and four-jet rates is studied using LEP data collected by the DELPHI experiment at the Z peak in 1994 and 1995. The rates of b-quark jets and light quark jets (ℓ = uds) in events with n=2, 3, and 4 jets, together with the ratio of two and four-jet rates of b-quarks with respect to light-quarks, Rnbℓ, have been measured with a double-tag technique using the CAMBRIDGE jet-clustering algorithm. A comparison between experimental results and theory (matrix element or Monte Carlo event generators such as PYTHIA, HERWIG and ARIADNE) is done after the hadronisation phase. Using the four-jet observable R4bℓ, a measurement of the b-quark mass using massive leading-order calculations gives: mb(MZ)=3.76±0. 32(stat)±0.17(syst)±0.22(had)±0.90(theo)GeV/c2. This result is compatible with previous three-jet determinations at the M Z energy scale and with low energy mass measurements evolved to the MZ scale using QCD renormalisation group equations. © 2008 Springer-Verlag / Società Italiana di Fisica.
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