A measurement of the b-quark mass from hadronic Z decays

Abstract.

Hadronic Z decay data taken with the ALEPH detector at LEP1 are used to measure the three-jet rate as well as moments of various event-shape variables. The ratios of the observables obtained from b-tagged events and from an inclusive sample are determined. The mass of the b quark is extracted from a fit to the measured ratios using a next-to-leading order prediction including mass effects. Taking the first moment of the $y_3$ distribution, which is the observable with the smallest hadronization corrections and systematic uncertainties, the result is\[m_b(M_{\mathrm Z}) = \left[3.27 \pm 0.22 (\mathrm{stat}) \pm 0.22 (\mathrm{exp}) \pm 0.38 (\mathrm{had}) \pm 0.16 (\mathrm{theo})\right] \;\gevcc\quad. \]

The measured ratio is alternatively employed to test the flavour independence of the strong coupling constant for b and light quarks.