Measurement of the tau polarization at the Z resonance

Using 18.8 pb−1 of data collected in 1990 and 1991, ALEPH has measured the tau polarisation in the decay modes τ→ev vˉ , τ→μv vˉ , τ→πν, τ→ρν and τ→a 1ν, using both the individual tau decay kinematics and the event acollinearity. The measurement of the tau polarisation as a function of the production polar angle yields the two parametersA τ andA e , whereA l =2g v l g A l /(g v l )2+(g A l )2] The resultsA τ=0.143±0.023 andA e =0.120±0.026 are consistent with the hypothesis of electron-tau universality. Assuming universality yields a measurement of the effective weak mixing angle sin2θ w eff=0.2332±0.0022

An Investigation into intermittency

The results of an investigation based on ALEPH data,e + e − → hadrons at s√=91 GeV, into fluctuations in rapidity space are presented. It is found that the behaviour of the factorial moments is well represented by the Lund parton shower model. An estimate is made of the scale of fluctuations needed to describe the data. Differential moments are introduced and are used to demonstrate that within the average represented by the traditional factorial moments the pattern of fluctuations is itself a strong function of rapidity. This pattern is shown to be primarily associated with the emission of hard gluons. The implied structure between the hadron clusters and partons is explored by the use of transverse mass moments. It is concluded that the principal features of the one-dimensional factorial moments, differential moments and transverse mass moments have their origin in theO(α s ) matrix element, kinematic boundaries and the method of selection of the event axis

Improved measurements of electroweak parameters fromZ decays into fermion pairs

The properties of theZ resonance are measured on the basis of 190 000Z decays into fermion pairs collected with the ALEPH detector at LEP. Assuming lepton universality,Mz=(91.182±0.009exp±0.020L∶P) GeV,ГZ=(2484±17) MeV, σhad0=(41.44±0.36) nb, andГjad/Гℓℓ=21.00±0.20. The corresponding number of light neutrino species is 2.97±0.07. The forward-back-ward asymmetry in leptonic decays is used to determine the ratio of vector to axial-vector coupling constants of leptons:gv2(MZ2)/gA2(MZ2)=0.0072±0.0027. Combining these results with ALEPH results on quark charge andbb ¯ asymmetries, and τ polarization, sin2θW(MZ2). In the contex of the Minimal Standard Model, limits are placed on the top-quark mass