Measurement of the Charged Multiplicity of $Z\to b\overline{b}$ Events

Abstract

Using an impact parameter tag to select an enriched sample of $Z\to b\overline{b}$ events, we have measured the difference between the average charged multiplicity of $Z\to b\overline{b}$ and $Z^0\to hadrons$ to be ${\overline{n}}_b-{\overline{n}}_{had}=2.24\pm 0.30(stat.)\pm 0.33(syst.)$ tracks per event. {}From this, we have derived ${\overline{n}}_b-{\overline{n}}_{uds}=3.31\pm 0.41\pm \mathrm{0.79.}$ Comparing this measurement with those at lower center-of-mass energies, we find no evidence that ${\overline{n}}_b-{\overline{n}}_{uds}$ depends on energy. This result is in agreement with a precise prediction of perturbative QCD, and supports the notion that QCD remains asymptotically free down to the scale $M_b^2$.

Comments: 15 pages (in Phyzzx) and two figures (uuencoded compressed EPS files), Physical Review Letters Volume 72, 3145 (May 1994), SLAC preprint SLAC-PUB-6372 (as revised for Physical Review Letters)