How Good are Present Analytical QCD-Predictions on Fluctuations in Angular Intervals ?

Results on two-particle angular correlations in jet cones and on multiplicity fluctuations in one- and two- dimensional angular intervals, delivered by three experiments (DELPHI, L3 and ZEUS, at $\sqrt{s}$ from few to 183 GeV) are compared to present existing analytical QCD calculations, using the LPHD hypothesis. Two different types of functions have been tested. While the differentially normalized correlation functions show substantial deviations from the predictions, a globally normalized correlation function agrees surprisingly well. The role of the QCD parameters $\alpha_s$, $\Lambda$ and $n_f$ is discussed. The necessity to include full energy-momentum conservation into the analytical calculations is stressed.Comment: 13 pages (LaTeX), 11 figures, uses sprocl.sty. Miniraporteur-talk given at the Internat. Symposium of Multiparticle Dynamics, Delphi, Greece, 6-11 Sept. 1998 (to appear in Proceedings

Study of gluon fragmentation and colour octet neutralization in DELPHI

Using the full statistics of the DELPHI experiment at $\sqrt{s}=91 GeV$ 3-jet events are selected and gluon respectively quark jet enriched subsamples are defined. The leading systems of the two kinds of jets are determined using rapidity gaps. The sum of charges of the leading systems is studied. It is found that for gluon-jets there is a significant excess of leading systems with total charge zero when compared to Monte Carlo simulations with JETSET. The corresponding leading systems of quark-jets do not exhibit such an excess. The mass spectra of the leading systems with total charge zero are studied.Comment: 8 pages, 6 figures (in eps) talk given at XXXI International Symposium on Multiparticle Dynamics, Sep. 1-7, 2001, Datong China URL http://ismd31.ccnu.edu.cn

Investigation of Bose-Einstein Correlations in 3 jet events with the DELPHI detector

A preliminary investigation of Bose-Einstein correlations in 3 jet events has been made by analysing the collected data at the $Z^0$ peak from '94 and '95 and the calibration runs during the LEP2 period from '97 to 2000. Three methods were used to extract two-particle correlation functions. No significant difference was found between quark and gluon jets for all three methods.Comment: 6 pages, 2 figures in ps and 1 in eps, talk given at XXXI International Symposium on Multiparticle Dynamics, Sept 1-7, 2001, Datong China. see http://ismd31.ccnu.edu.cn

Intermittency in a single event

The possibility to study intermittency in a single event of high multiplicity is investigated in the framework of the $\alpha-$model. It is found that, for cascade long enough, the dispersion of intermittency exponents obtained from individual events is fairly small. This fact opens the possibility to study the distribution of the intermittency parameters characterizing the cascades seen (by observing intermittency) in particle spectra.Comment: 7 pages, latex, 2 figures available on request by e-mai

Internal cumulants for femtoscopy with fixed charged multiplicity

A detailed understanding of all effects and influences on higher-order correlations is essential. At low charged multiplicity, the effect of a nonpoissonian multiplicity distribution can significantly distort correlations. Evidently, the reference samples with respect to which correlations are measured should yield a null result in the absence of correlations. We show how the careful specification of desired properties necessarily leads to an average-of-multinomials reference sample. The resulting internal cumulants and their averaging over several multiplicities fulfil all requirements of correctly taking into account nonpoissonian multiplicity distributions as well as yielding a null result for uncorrelated fixed-N samples. Various correction factors are shown to be approximations at best. Careful rederivation of statistical variances and covariances within the frequentist approach yields errors for cumulants that differ from those used so far. We finally briefly discuss the implementation of the analysis through a multiple event buffer algorithm.Comment: 33 pages, 3 figures, 79 reference