ISSN:
1434-6052
Source:
Springer Online Journal Archives 1860-2000
Topics:
Physics
Notes:
Abstract The forward-backward asymmetry of $$e^ + e^ - \to Z^0 \to b\bar b$$ has been measured using approximately 2.15 million hadronicZ 0 decays collected at the LEP e+e− collider with the OPAL detector. A lifetime tag technique was used to select an enriched $$b\bar b$$ event sample. The measurement of the $$b\bar b$$ asymmetry was then performed using a jet charge algorithm to determine the direction of the primary quark. Values of: $$\begin{gathered} A_{FB}^b = 0.062 \pm 0.034 \pm 0.002 - 0.082\Delta (\Gamma _{b\bar b} /\Gamma _{had} ) \hfill \\ at\sqrt s = 89.52GeV, \hfill \\ A_{FB}^b = 0.0963 \pm 0.0067 \pm 0.0038 - 0.471\Delta (\Gamma _{b\bar b} /\Gamma _{had} ) \hfill \\ at\sqrt s = 91.25GeV, \hfill \\ A_{FB}^b = 0.172 \pm 0.028 \pm 0.007 - 0.055\Delta (\Gamma _{b\bar b} /\Gamma _{had} ) \hfill \\ at\sqrt s = 92.94GeV, \hfill \\ \end{gathered}$$ were measured where, in each case, the first error is statistical, the second is systematic and the third term gives the variation due to a change $$\Delta (\Gamma _{b\bar b} /\Gamma _{had} )$$ in the value of $$\Gamma _{b\bar b} /\Gamma _{had} = 0.216$$ assumed. The dependence on the assumed charm asymmetry at the same energy is Δ(A FB b )≈+0.07Δ(A FB c ). Assuming the Standard Model form for the couplings, these measurements correspond to an effective weak mixing angle of: $$\sin ^2 \theta _W^{eff,e} = 0.2313 \pm 0.0012 \pm 0.0006$$ giving Mtop=196 −38−19 +33+16 GeV/c 2, where the first error is statistical and the second is systematic. The Higgs mass assumed is 300 GeV/c 2. A variation in the assumed mass of the Higgs boson between 60 and 1000 GeV/c 2 corresponds to an uncertainty in sin2θ W eff,e of ±0.00006 and on Mtop of −26 +20 GeV/c 2.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01624580
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