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Bose-Einstein correlations in W-pair decays are studied using data collected by the ALEPH detector at LEP at e+e- centre-of-mass energies from 183 to 209 GeV. The analysis is based on the comparison of WW-->qqqq events to ``mixed'' events constructed with the hadronic part of WW-->qqlnu events. The data are in agreement with the hypothesis that Bose-Einstein correlations are present only for pions from the same W decay. The JETSET model with Bose-Einstein correlations between pions from different W bosons is disfavoured.
The acoplanar photon pairs produced in the reaction e(+) e(-) - → vvyy are analysed in the 700 pb(-1) of data collected by the ALEPH detector at centre-of-mass energies between 183 and 209 GeV. No deviation from the Standard Model predictions is seen in any of the distributions examined. The resulting 95% C.L. limits set on anomalous QGCs, a(0)(Z), a(c)(Z), a(0)(W) and a(c)(W), are -0.012 lt a(0)(Z)/Lambda(2) lt +0.019 GeV-2, -0.041 lt a(c)(Z)/Lambda(2) lt +0.044 GeV-2, -0.060 lt a(0)(W)/Lambda(2) lt +0.055 GeV-2, -0.099 lt a(c)(W)/Lambda(2) lt +0.093 GeV-2, where Lambda is the energy scale of the new physics responsible for the anomalous couplings.
Bose-Einstein correlations are studied in pairs of charged pions from hadronic Z decays, collected by the ALEPH detector. The correlation function, measured using either the unlike-sign or the mixed reference sample, is studied in terms of the Lorentz-invariant four-momentum difference and its transverse, Q(T), and longitudinal, Q(L), components with respect to the longitudinal centre-of-mass system. Values for the correlation radii, R-T and R-L, are obtained from the fit of the Goldhaber parametrisation. The results indicate that the correlation radii values depend on the chosen kind of reference sample and on the two-jet purity.
The hadronic final states observed with the ALEPH detector at LEP in e(+)e(-) annihilation are analysed using 730 pb(-1) of data collected between 91 and 209 GeV in the framework of QCD. In particular event-shape variables and inclusive charged particle spectra are measured. The energy evolution of quantities derived from these measurements is compared to analytic QCD predictions. The mean charged particle multiplicity, the charged particle momentum spectrum and its peak position are compared to predictions of the modified- leading-logarithmic approximation. The strong coupling constant alpha(s) is determined from a fit of the QCD prediction to distributions of six event-shape variables at eight centre-of- mass energies. A study of non-perturbative power law corrections is presented.
The properties of the Z resonance are measured from the analysis of 4.5 million Z decays into fermion pairs collected with the ALEPII detector at LEP. The data are consistent with lepton universality. The resonance parameters are measured to be M-Z = (91.1885 +/- 0.0031) GeV/c(2), Gamma(Z) = (2.4941 +/- 0.0043) GeV, sigma(had)(0) = (41.559 +/- 0.058) nb and, combining the three lepton flavours, R-l = 20.725 +/- 0.039. The corresponding number of light neutrino species is N-v = 2.983 +/- 0.013 and the strong coupling constant is alpha(s)(M- Z) = 0.114 +/- 0.004 +/- 0.002(QCD) + 0.005 log(10) [M-H/150 GeV/c(2)]. The lepton pair forward-backward asymmetry is measured to be A(FB)(0,l) = 0.0173 +/- 0.0016 from which the effective weak mixing angle is described: sin(2) theta(eff)(lept) = 0.23089 +/- 0.00089. The measurement of the leptonic w...
An experimental investigation of the structure of identified quark and gluon jets is presented. Observables related to both the global and internal structure of jets are measured; this allows for tests of QCD over a wide range of transverse momentum scales. The observables include distributions of jet- shape variables, the mean and standard deviation of the subjet multiplicity distribution and the fragmentation function for charged particles. The data are compared with predictions of perturbative QCD as well as QCD-based Monte Carlo models. In certain kinematic regions the measurements are sensitive mainly to perturbatively calculable effects, allowing for a test of QCD. The comparisons are also extended into regions where nonperturbative effects become large, and in this way the transition from hard to soft QCD is investigated. It is ...
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