Improved tau polarisation measurement
European Physical Journal C(2014)
摘要
Using 22 pb−1 of data collected at LEP in 1992 on the peak of the Z resonance, the ALEPH collaboration has measured the polarisation of
the tau leptons decaying into
$$ev\bar v, \mu v\bar v$$
,πν, ρν and a1
ν from their individual decay product distributions. The measurement of the tau polarisation as a function of the production
polar angle yields the two parametersN
τ andN
e, where, in terms of the axial and vector couplingsg
Al andg
Vl,N
l=2g
Vl gAl/(g
Vl
2
+g
Al
2
). This analysis follows to a large extent the methods devised for the 1990 and 1991 data but with improvements which bring
a better understanding of the systematic uncertainties. Combining the 1992 measurements with our previously published results
yieldsN
τ=0.136±0.012±0.009 andN
e=0.129±0.016±0.005. Assuminge−τ universality, the measurements imply an effective weak mixing angle of sin
2
θ
W
eff
=0.2332±0.0014.
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关键词
Systematic Uncertainty, Time Projection Chamber, Charged Track, Particle Identification, Aleph Collaboration
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