PII: 0370-2693(87)90324-8

A study has been made of the decays W--,ev and Z--,e+e -, using the UA2 detector at the CERN 13p Collider. The data correspond to an integrated luminosity of 142 nb-~ at a centre-of-mass collision energy v/~= 546 GeV, and 768 nb-~ at V/~= 630 GeV. Measurements of the standard model parameters from samples of 251 W decay and 39 Z decay candidates are compared with expectations of the standard electroweak model. On leave from Scoula Normal

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

Study of the four fermion final state at the Z resonance

The process e+e−→, where l is a charged or a neutral lepton and f any charged fermion, is analyzed. The study uses the ALEPH data collected at LEP from 1989 to 1993 at centre-of-mass energies between 88 and 95 GeV, corresponding to almost two million hadronic Z decays and to a total integrated luminosity of 79 pb−1. For all channels, the data agree well with the standard model expectation both in shape and normalization. The indication of an excess in the e+e−→τ+τ−ffˉ channel, reported by ALEPH in 1991, is not confirmed

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