Abstract
The b quark forward–backward asymmetry has been measured using hadronic Z0 decays collected by the OPAL experiment at LEP. Z0→bb̄ decays were selected using a combination of secondary vertex and lepton tags, and the sign of the b quark charge was determined using an inclusive tag based on jet, vertex and kaon charges. The results, corrected to the quark level, are: AFBb=0.0582±0.0153±0.0012ats=89.50GeV,AFBb=0.0977±0.0036±0.0018ats=91.26GeV,AFBb=0.1221±0.0123±0.0025ats=92.91 GeV, where the first error is statistical and the second systematic in each case. Within the framework of the Standard Model, the result is interpreted as a measurement of the effective weak mixing angle for electrons of sin2θeff,eW=0.23205±0.00068.
Highlights
AsyTmhme emtreyasoufrebmeqnutaorkf sApbFBro,dtuhceefdoriwnared+–eb−ac→ kwabrbdevents, provides an important test of the Standard Model, allowing the effective weak mixing angle sin2 θWeff to be determined with high precision [1]
With the values of the electron and b quark couplings predicted in the Standard Model, the asymmetry AbF,B0 is mainly sensitive to the weak mixing angle for electrons, sin2 θWeff,e, and insensitive to that for b quarks
This Letter reports a measurement of AbFB using jet, vertex and kaon charges combined in an inclusive tag, which incorporates several improvements over the previous OPAL analysis using jet and vertex charges [3]
Summary
AsyTmhme emtreyasoufrebmeqnutaorkf sApbFBro,dtuhceefdoriwnared+–eb−ac→ kwabrbdevents, provides an important test of the Standard Model, allowing the effective weak mixing angle sin θWeff to be determined with high precision [1]. With the values of the electron and b quark couplings predicted in the Standard Model, the asymmetry AbF,B0 is mainly sensitive to the weak mixing angle for electrons, sin θWeff,e, and insensitive to that for b quarks. The weak mixing angle sin θWeff,e can be determined from the measured asymmetry within the context of the Standard Model, which predicts the centre-ofmass energy dependence of the asymmetry arising from Z0-γ interference [1]. The most sensitive measurements of sin θWeff,e at LEP come from the measurements of the b quark asymmetry, using techniques based on jet charges, secondary vertices and high momentum leptons [2,3,4].
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