EPJ

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EPJ C - Particles and Fields
Particles and Fields


Eur. Phys. J. C 21, 411-422 (2001)
DOI: 10.1007/s100520100746

Determination of the b quark mass at the Z mass scale

The OPAL Collaboration G. Abbiendi and et al.

Dipartimento di Fisica dell' Università di Bologna and INFN, 40126 Bologna, Italy

(Received: 14 May 2001 / Published online: 17 August 2001 -© Springer-Verlag / Società Italiana di Fisica 2001 )

Abstract
In hadronic decays of Z bosons recorded with the OPAL detector at LEP, events containing b quarks were selected using the long lifetime of b flavoured hadrons. Comparing the 3-jet rate in b events with that in d,u,s and c quark events, a significant difference was observed. Using ${\cal O}(\alpha_{\mathrm{S}}^2)$ calculations for massive quarks, this difference was used to determine the b quark mass in the ${\overline{\mathrm{{MS}}}}$ renormalisation scheme at the scale of the Z boson mass. By combining the results from seven different jet finders the running b quark mass was determined to be ${\overline{m}_{b}}({m_{Z}}) = (2.67 \pm 0.03{\mathrm{(stat.)}} ^{+0.29}_{-0.37}{\mathrm{(syst.)}} \pm 0.19{\mathrm{(theo.)}}){\mathrm{ GeV}}$. Evolving this value to the b quark mass scale itself yields ${\overline{m}_{b}}({\overline{m}_{b}}) = (3.95 ^{+0.52}_{-0.62}){\mathrm{ GeV}}$, consistent with results obtained at the b quark production threshold. This determination confirms the QCD expectation of a scale dependent quark mass. A constant mass is ruled out by 3.9 standard deviations.



© Società Italiana di Fisica, Springer-Verlag 2001

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