Determination of the b quark mass at the Z mass scale
2001
In hadronic decays of Z bosons recorded with the OPAL detector at LEP, events containing b
quarkswere 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
quarkevents, a significant difference was observed. Using \({\cal O}(\alpha_{\mathrm{S}}^2)\) calculations for massive
quarks, this difference was used to determine the b
quarkmass 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
quarkmass 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
quarkmass scale itself yields \({\
overline{m}_{b}}({\
overline{m}_{b}}) = (3.95 ^{+0.52}_{-0.62}){\mathrm{ GeV}}\), consistent with results obtained at the b
quarkproduction threshold. This determination confirms the QCD expectation of a scale dependent
quarkmass. A constant mass is ruled out by 3.9 standard deviations.
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