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Register a new userFour Fermion processes at LEP II
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V. Verzi
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In its second phase, LEP has given the unique opportunity to study four fermion processes never observed before. This papers deals with a preliminary study of $WW$, $We u$, $ZZ$ and $Zgamma^star$ production in $e^+e^-$ collisions. Measurement results on $WW$ cross section, $W$ branching fractions, $WWV$ ($V=Z/gamma$) anomalous couplings and $W$ average polarization in $WW$ events are presented. Moreover cross section measurements for $We u$, $ZZ$ and $Zgamma^star$ production and limits on $ZZZ$ and $ZZgamma$ anomalous couplings are reported. All the results are in good agreement with the Standard Model expectations.
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The four LEP experiments ALEPH, DELPHI, L3 and OPAL successfully recorded e+e- collision data during the years 1989 to 2000. As part of the ordinary evolution in High Energy Physics, these experiments can not be repeated and their data is therefore unique. This article briefly reviews the data preservation efforts undertaken by the four experiments beyond the end of data taking. The current status of the preserved data and associated tools is summarised.
Selected topics on precision tests of the Standard Model of the Electroweak and the Strong Interaction at the LEP $e^+e^-$ collider are presented, including an update of the world summary of measurements of $alpha_s$, representing the state of knowledge of summer 1999. This write-up of lecture notes consists of a reproduction of slides, pictures and tables, supplemented by a short descriptive text and a list of relevant references.
New results on inclusive production of Sigma^- and Lambda(1520) and on proton production in quark and gluon jets are presented. These results are based on 2 million hadronic Z decays collected with the DELPHI detector at LEP. They are compared with the results of other LEP experiments and with models. It has been shown that the total production rates of all light-flavour hadrons measured so far at LEP 1 follow phenomenological laws related to the spin, isospin, strangeness and mass of the particles. A significant proton enhancement in gluon jets is observed, indicating that baryon production proceeds directly from colour objects.
A study of the inclusive charged hadron production in two-photon collisions is described. The data were collected with the DELPHI detector at LEP II. Results on the inclusive single-particle p_T distribution and the differential charged hadrons dsigma/dp_T cross-section are presented and compared to the predictions of perturbative NLO QCD calculations and to published results.
Bose-Einstein correlations in pairs of identical particles were analyzed in e+ e- multihadron annihilations at ~91.2 GeV at LEP. The first studies involved identical charged pions and the emitting source size was determined. Then the study of charged kaons suggested that the radius depends on the mass of the emitted particles. Subsequenty the dependence of the source radius on the event multiplicity was analyzed. The study of the correlations in neutral pions and neutral kaons extended these concepts to neutral particles. The shape of the source was analyzed in 3 dimensions and was found not to be spherically symmetric. In recent studies at LEP the correlations were analyzed in intervals of the average pair transverse momentum and of the pair rapidity to study the correlations between the pion production points and their momenta (position-momentum correlations). The latest e+ e- data are consistent with an expanding source.
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