Cosmic-ray positron fraction measurement from 1 to 30 GeV with AMS-01

A measurement of the cosmic ray positron fraction e+ / (e+ + e-) in the energy range of 1-30 GeV is presented. The measurement is based on data taken by the AMS-01 experiment during its 10 day Space Shuttle flight in June 1998. A proton background suppression on the order of 106 is reached by identifying converted bremsstrahlung photons emitted from positrons.ISSN:0370-2693ISSN:0031-9163ISSN:1873-244

Measurement of W polarisation at LEP

The three different helicity states of W bosons produced in the reaction e+e- →W+W-→lνqq-' at LEP are studied using leptonic and hadronic W decays. Data at centre-of-mass energies √s = 183-209 GeV are used to measure the polarisation of Wbosons, and its dependence on theWboson production angle. The fraction of longitudinally polarisedWbosons is measured to be 0.218 ± 0.027 ± 0.016 where the first uncertainty is statistical and the second systematic, in agreement with the Standard Model expectation.ISSN:0370-2693ISSN:0031-9163ISSN:1873-244

Search for colour reconnection effects in e+e- -> W+W- -> hadrons through particle-flow studies at LEP

A search for colour reconnection effects in hadronic decays of W pairs is performed with the L3 detector at centre-of-mass energies between 189 and 209 GeV. The analysis is based on the study of the particle flow between jets associated to the sameW boson and between two different W bosons in qqqq events. The ratio of particle yields in the different interjet regions is found to be sensitive to colour reconnection effects implemented in some hadronization models. The data are compared to different models with and without such effects. An extreme scenario of colour reconnection is ruled out.ISSN:0370-2693ISSN:0031-9163ISSN:1873-244