Intermittency and correlations in hadronic Z $^0$ decays

Abstract

Abstract.A multidimensional study of local multiplicity fluctuations and multiparticle correlations of hadrons produced in Z 0 decays is performed. The study is based on the data sample of more than 4×106 events recorded with the OPAL detector at LEP. The fluctuations and correlations are analysed in terms of the normalized scaled factorial moments and cumulants up to the fifth order. The moments are observed to have intermittency-like behaviour, which is found to be more pronounced with increasing dimension. The large data sample allows for the first time a study of the factorial cumulants in e + e − annihilation. The analysis of the cumulants shows the existence of genuine multiparticle correlations with a strong intermittency rise up to higher orders. These correlations are found to be stronger in higher dimensions. The decomposition of the factorial moments into lower-order correlations shows that the dynamical fluctuations have important contributions from genuine many-particle correlations. The Monte Carlo models Jetset 7.4 and Herwig 5.9 are found to reproduce the trend of the measured moments and cumulants but they underestimate the magnitudes. The results are found to be consistent with QCD jet formation dynamics, although additional contributions from other mechanisms cannot be excluded. 240The OPAL Collaboration: Intermittency and correlations in hadronic Z 0 decays

Precision electroweak measurements on the Z resonance

“…L3 identifies b-hemispheres using the impact parameter tag only [124]. OPAL uses a vertex tag based on a neural network combining five variables [125]. The first four are derived from the reconstructed secondary vertex: the decay length significance L/σ L , the decay length L, the number of tracks in the secondary vertex and a variable that measures the stability of the vertex against mismeasured tracks.…”

Genuine pion–pion correlations in heavy-ion collisions

“…Thus, they automatically remove any contribution due to Poissonian fluctuations, and any deviation from zero for a given cumulant indicates the presence of the non-statistical correlation of that order. In this context, it should be mentioned that the search for the genuine higher order correlation has been studied in e + e − collisions by the OPAL collaboration [9]. They have established the existence of strong genuine multihadron correlations up to the fifth order.…”

Three-particle correlations in QCD jets and beyond

“…The evolution equations satisfied by (9) are derived from the MLLA master equation for the generating functional Z A (u(k i )) (1). In this case, one takes the first δZ A δu(k 1 ) , second δ 2 Z A δu(k 1 )δu(k 2 ) and finally third δ 3 Z A δu(k 1 )...δu(k 3 ) functional derivatives of Z A (u(k i )) over the probing functions u(k i ) so as to obtain the system of evolution equations for three-particle correlations.…”

“…In this case, one takes the first δZ A δu(k 1 ) , second δ 2 Z A δu(k 1 )δu(k 2 ) and finally third δ 3 Z A δu(k 1 )...δu(k 3 ) functional derivatives of Z A (u(k i )) over the probing functions u(k i ) so as to obtain the system of evolution equations for three-particle correlations. Following from (1), after applying the operator δ 3 δu(k 1 )...δu(k 3 ) to both members of the equation, according to (9) and (10) together with the initial condition (7), it is straightforward to get the coupled system of evolution equations: (3) (z) − G (3) )…”

“…Powerful schemes, like the double logarithmic approximation (DLA) and the modified leading logarithmic approximation (MLLA), which allow for the perturbative resummation of softcollinear and hard-collinear gluons before hadronization occurs, have been developed over the past 30 years (for a review see [5]). One of the most striking predictions of perturbative QCD, which follows as a consequence of angular ordering (AO) within the MLLA and the local parton hadron duality (LPHD) hypothesis [6], is the existence of the hump-backed shape [7] of the inclusive energy distribution of hadrons, later confirmed by experiments at colliders like the LEP [8,9] and the Tevatron [10]. Indeed, the shape and normalization of single inclusive distributions are compared with an experiment; a constant K ch , which normalizes the number of soft gluons to the number of charged detected hadrons (mostly pions and kaons), turns out to be close to unity (K ch ∼ 1), thus giving support to the similarity between parton and hadron spectra [5].…”