Hadron production and QCD coherence at LEP

Hadron production in two-photon collisions at LEP-L3∗

The reaction ee → eeγγ → ee hadrons is analysed for quasi-real virtual photons using data collected by the L3 detector during the LEP high energy runs at √ s = 183 and 189 GeV. Preliminary results on the cross sections σ(ee → ee hadrons) and σ(γγ → hadrons) are given in the interval 5 GeV ≤ Wγγ ≤ 145 GeV. The centre-of-mass energy dependence of the two-photon cross section is well described by ...

b-HADRON PHYSICS AT LEP

Modelling the fragmentation process in Monte Carlo is a source of systematic error to many LEP b-physics analyses e.g. |Vub|. Constraining this error from data measurements is therefore important and in the last few years precise measurements have begun to appear e.g. from ALEPH1 using the semi-exclusive reconstruction of B → Dlν̄l a decays and from SLD2 using a fully inclusive approach. The fra...

QCD at LEP*

Qcd at Lep

This lecture is a brief introductory to QCD at Lep. It is shown, how the basic properties of strongly interacting elds have been veriied at Lep and how the strong coupling is measured from event shapes. Important properties of the hadronic nal state, namely the energy evolution of fragmentation functions and of multiplici-ties as well as the importance of coherence eeects are discussed. The con...

Test of Qcd Predictions for Multiparticle Production at Lep

The constants b and c entering in this expression can be calculated, and especially in the result for c enters crucially the assumption of coherence: neglecting the effect of angular ordering would increase it by a factor of √ 2. The data up to the highest energies keep to be in fair agreement with this prediction 1 (see Fig.1). An important point in this measurement is that the LEP data have b...