The DELPHI detector at LEP has collected 54 pb(-1) of data at a centre-of-m
ass energy around 183 GeV during 1997, 158 pb(-1) around 189 GeV during 199
8, and 187 pb(-1) between 192 and 200 GeV during 1999. These data were used
to measure the average charged particle multiplicity in e(+)e(-)->b (b) ov
er bar events: (n)(b (b) over bar), and the difference delta(hl) between (n
)(b (b) over bar) and the multiplicity, (n)(l (l) over bar), in generic lig
ht quark (u,d,s) events:
delta(hl)(183 GeV) = 4.55 +/- 1.31(stat) +/- 0.73(syst),
delta(hl)(189 GeV) = 4.43 +/- 0.85(stat) +/- 0.61(syst),
delta(hl)(200 GeV) = 3.39 +/- 0.89(stat) +/- 1.01 (syst).
This result is consistent with QCD predictions, while it is inconsistent wi
th calculations assuming that the multiplicity accompanying the decay of a
heavy quark is independent of the: mass of the quark itself. (C) 2000 Elsev
ier Science B.V. All rights reserved.