T. Novak

Parametrization of Bose-Einstein correlations and reconstruction of the space-time evolution of pion production in e(+)e(-) annihilation

Abstract A parametrization of the Bose–Einstein correlation function of pairs of identical pions produced in hadronic e + e − annihilation is proposed within the framework of a model (the τ -model) in which space–time and momentum space are very strongly correlated. Using information from the Bose–Einstein correlations as well as from single-pion spectra, it is then possible to reconstruct the space–time evolution of pion production.

Measurement of the running of the electromagnetic coupling at large momentum-transfer at LEP

The evolution of the electromagnetic coupling, alpha, in the momentum-transfer range 1800GeV^2<-Q^2<21600GeV^2 is studied with about 40000 Bhabha-scattering events collected with the L3 detector at LEP at centre-of-mass energies 189-209GeV. The running of alpha is parametrised as: alpha(Q^2) = alpha_0/(1-C Delta alpha(Q^2)), where alpha_0=alpha(Q^2=0) is the fine-structure constant and C=1 corresponds to the evolution expected in QED. A fit to the differential cross section of the e+e- ->e+e- process for scattering angles in the range |cos theta|<0.9 excludes the hypothesis of a constant value of alpha, C=0, and validates the QED prediction with the result: C = 1.05 +/- 0.07 +/- 0.14, where the first uncertainty is statistical and the second systematic.