The charged particle multiplicity distribution of hadronic Z decays was measured on the peak of the Z resonance using the ALEPH detector at LEP. Using a model independent unfolding procedure the distribution was found to have a mean 〈 n 〉=20.85±0.24 and a dispersion D =6.34±0.12. Comparison with lower energy data supports the KNO scaling hypothesis in the energy range s =29−91.25 GeV. At s =91.25 GeV the shape of the multiplicity distribution is well described by a log-normal distribution, as predicted from a cascading model for multi-particle production. The same model also successfully describes the energy dependence of the mean and width of the multiplicity distribution. A next-to-leading order QCD prediction in the framework of the modified leading-log approximation and local parton-hadron duality is found to fit the energy dependence of the mean but not the width of the charged multiplicity distribution, indicating that the width of the multiplicity distribution is a sensitive probe for higher order QCD or non-perturbative effects.
Unfolded charged particle multiplicity distribution. The entry for N=2 is from the LUND 7.2 parton shower model.
Leading moments of the charged particle multiplicity. R2 is the second binomial moment given by MEAN(MULT(MULT-1))/(MEAN(MULT))**2.
The hadronic final states observed with the ALEPH detector at LEP in ${\rm e}^ + {\rm e}^-$ annihilation
Mean charged particle multiplicities at different c.m. energies.
XP distribution at c.m. energy 133.0 GeV.
XP distribution at c.m. energy 161.0 GeV.
Charged particle multiplicity distributions have been measured with the ALEPH detector in restricted rapidity intervals |Y| ≤0.5, 1.0, 1.5, 2.0 along the thrust axis and also without restriction on rapidity. The distribution for the full range can be parametrized by a log-normal distribution. For smaller windows one finds a more complicated structure, which is understood to arise from perturbative effects. The negative-binomial distribution fails to describe the data both with and without the restriction on rapidity. The JETSET model is found to describe all aspects of the data while the width predicted by HERWIG is in significant disagreement.
Unfolded charged particle multiplicity distribution given the probability to have an hadronic Z0 decay with MULT charged particles.
Unfolded multiplicity distributions for restricted rapidity bin <= 0.5 along the thrust axis.
Unfolded multiplicity distributions for restricted rapidity bin <= 1.0 along the thrust axis.
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Inclusive charged particle distribution as a function of XP.
Inclusive charged particle distribution as a function of rapidity (YRAP).
Inclusive charged particle distribution as a function of PT in the event plane.
Previously published and as yet unpublished QCD results obtained with the ALEPH detector at LEP1 are presented. The unprecedented statistics allows detailed studies of both perturbative and non-perturbative aspects of strong interactions to be carried out using hadronic Z and tau decays. The studies presented include precise determinations of the strong coupling constant, tests of its flavour independence, tests of the SU(3) gauge structure of QCD, study of coherence effects, and measurements of single-particle inclusive distributions and two-particle correlations for many identified baryons and mesons.
Charged particle sphericity distribution.
Charged particle aplanarity distribution.
Charged particle Thrust distribution.
We have measured theR value in non-resonante+e− annihilation using the ARGUS detector at the storage ring DORIS II. At a centre-of-mass energy\(\sqrt s= 9.36\) GeV the ratio of the hadronic cross-section to the μ-pair cross section in lowest order QED has been determined to beR=3.46±0.03±0.13. In addition, we have measured the charged-particle multiplicities in non-resonant hadron production at\(\sqrt s= 10.47\) GeV just below theB\(\bar B\) threshold and in ϒ (4S) resonance decays. For the average charged-particle multiplicities in continuum events and ϒ(4S)→B\(\bar B\) decays we obtain <n>cont=8.35±0.02±0.20 and <n>ϒ(4s)=10.81±0.05±0.23.
Corrected for radiative effects and acceptance.
Unfolded charged particle multiplicity distribution for continuum events.
Unfolded charged particle multiplicity distribution for UPSILON(4S) events.
The multiplicity distributions of charged particles in full phase space and in restricted rapidity intervals for events with a fixed number of jets measured by the DELPHI detector are presented. The data are well reproduced by the Lund Parton Shower model and can also be well described by fitted negative binomial distributions. The properties of these distributions in terms of the clan model are discussed. In symmetric 3-jet events the candidate gluon jet is found not to be significantly different in average multiplicity than the mean of the other two jets, thus supporting previous results of the HRS and OPAL experiments. Similar results hold for events generated according to the LUND PS and to the HERWIG models, when the jets are defined by the JADE jet finding algorithm. The method seems to be insensitive for measuring the color charge ratio between gluons and quarks.
Corrected charged particle multiplicity for jet resolution parameter YCUT = 0.01.
Corrected charged particle multiplicity for jet resolution parameter YCUT = 0.02.
Corrected charged particle multiplicity for jet resolution parameter YCUT = 0.04.
The multiplicity distributions of charged particles in restricted rapidity intervals inZ0 hadronic decays measured by the DELPHI detector are presented. The data reveal a shoulder structure, best visible for intervals of intermediate size, i.e. for rapidity limits around ±1.5. The whole set of distributions including the shoulder structure is reproduced by the Lund Parton Shower model. The structure is found to be due to important contributions from 3-and 4-jet events with a hard gluon jet. A different model, based on the concept of independently produced groups of particles, “clans”, fluctuating both in number per event and particle content per clan, has also been used to analyse the present data. The results show that for each interval of rapidity the average number of clans per event is approximately the same as at lower energies.
Data for both hemispheres.
Data for both hemispheres.
Data for both hemispheres.
This paper presents an analysis of the multiplicity distributions of charged particles produced inZ0 hadronic decays in the DELPHI detector. It is based on a sample of 25364 events. The average multiplicity is <nch>=20.71±0.04(stat)±0.77(syst) and the dispersionD=6.28±0.03(stat)±0.43(syst). The data are compared with the results at lower energies and with the predictions of phenomenological models. The Lund parton shower model describes the data reasonably well. The multiplicity distributions show approximate KNO-scaling. They also show positive forward-backward correlations that are strongest in the central region of rapidity and for particles of opposite charge.
Charged particle multiplicity distribution for the raw data in full phase space.
Charged particle multiplicity distribution for full phase space. Errors include systematics. A 2 pct correction for excess electrons from photon conversions is not included. The first two points, at N=2 and 4, were not measured but taken from the Lund PS model.
Charged particle multiplicity distribution for single hemisphere. Errors include systematics. A 2 pct correction for excess electrons from photon conversions is not included.
Event shape and charged particle inclusive distributions are measured using 750000 decays of the Z to hadrons from the DELPHI detector at LEP. These precise data allow a decisive confrontation with models of the hadronization process. Improved tunings of the JETSET, ARIADNE and HERWIG parton shower models and the JETSET matrix element model are obtained by fitting the models to these DELPHI data as well as to identified particle distributions from all LEP experiments. The description of the data distributions by the models is critically reviewed with special importance attributed to identified particles.
Transverse momentum PTIN w.r.t. the Thrust axis. For the first table Thrust axis definition is from seen charged particles corrected to final state particles. For the second table Thrust axis definition is from seen charged plus neutral particles corrected to final state charged plus neutral particles.
Transverse momentum PTOUT w.r.t. the Thrust axis. For the first table Thrust axis definition is from seen charged particles corrected to final state particles. For the second table Thrust axis definition is from seen charged plus neutral particles corrected to final state charged plus neutral particles.
Transverse momentum PTIN w.r.t. the Sphericity axis. For the first table Sphericity axis definition is from seen charged particles corrected to final state particles. For the second table Sphericity axis definition is from seen charged plus neutral particles corrected to final state charged plus neutral particles.
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