M. Schmelling

QCD results from the study of hadronic Z-decays

The high statistics data collected from hadronic Z-decays have lead to remarkable progress in the understanding of the dynamics of strong interactions. In addition to precision measurements of the strong coupling constant, the colour factors defining the gauge structure of QCD were determined with large accuracy. They are found to agree with the expectation for an unbroken SU(3) symmetry, thus establishing unambiguously the non-abelian nature of QCD. Higher order effects in many cases are known to next-to-leading logarithmic precision. Coherence effects as predicted in the framework of the modified leading-log approximation and local parton-hadron duality are experimentally well established. Studies of the hadronization process favour a chain-like production mechanism which bridges the gap between perturbative QCD as described by coherent parton shower models and the final state hadrons.

Averaging correlated data

The problem of averaging strongly correlated data is addressed for the case that the exact correlation pattern is unknown. A procedure is proposed to estimate the effective size of the correlations from the data themselves and to take them properly into account when forming the average. The properties of the procedure are illustrated by using it for averaging measurements of the strong coupling constant and QCD colour-factor ratios.

An improved theoretical prediction for the 2-jet rate in e+e− annihilation

Abstract We show that an Ansatz to resum all leading and next-to-leading logarithms in the theoretical prediction for the 2-jet rate in e + e − → hadrons, where jets are defined with the k t -algorithm, is consistent with a full O ( α s 2 ) calculation done by Monte Carlo integration. From the asymptotic behaviour of the full O ( α s 2 ) calculation we extract the subleading coefficient G 21 and the constant C 2 .

The method of reduced cross-entropy A general approach to unfold probability distributions

Abstract A new unfolding method is presented for the case where the unfolded distribution is known to be non-negative everywhere. The method combines the least-squares method with the principle of minimum cross-entropy. Its properties are discussed together with an algorithm for its realization and illustrated by means of a numerical example.

Charged multiplicity distributions in rapidity bins for pp collisions at

SummaryThe multiplicity distributions of charged secondaries in proton-proton interactions at

and 62 GeV

\sqrt s = 31

The FASTBUS readout system for the Aleph time projection chamber

, 44 and 62 GeV have been measured with high statistics using the split field magnet (SFM) detector at the CERN ISR. The multiplicity distributions for narrow bins in rapidity depend on the rapidity variable. The validity of KNO scaling is discussed. The negative binomial function fits well the charged and negative multiplicity data for full phase space and for central rapidity windows. The energy and the rapidity dependence of the negative binomial parameters,