Lund Model Research Articles

QCD demonstration for the color string structures of e+e--->qq-barg and Upsilon -->3g systems.

The ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}q\overline{q}g\ensuremath{\rightarrow}3$ jets and $\ensuremath{\Upsilon}\ensuremath{\rightarrow}3g\ensuremath{\rightarrow}\mathrm{hadrons}$ processes are well suited to the study of the gluon hadronization mechanism. In the LUND model, these two processes are treated by applying the string fragmentation model to the assumed color string structure of $q\overline{q}g$ and $3g$ systems. In this paper, the color string structure of the $q\overline{q}g$ and $\mathrm{ggg}$ systems is given by directly analyzing their color wave functions in the context of perturbative QCD. In addition, the reasonableness and accuracy of the LUND string pictures are discussed.

Multiplicity and rapidity density in central collisions of 4.1 A GeV c-1 22Ne nuclei in nuclear emulsions

The multiplicity and pseudo-rapidity distributions of hadrons produced in central collisions of 4.1 A GeV c-1 22Ne nuclei in nuclear emulsion are studied. The KNO scaled multiplicity distribution of the produced hadrons is compared with the predicted distributions according to the Lund model, dual parton model (DPM) and the negative binomial law. The negative binomial method seems to offer a better representation of the experimental data at 4.1 A GeV c-1. The energy density is calculated according to the Bjorken model and found to be less than the estimated energy density required for the transformation into the quark-gluon plasma phase.

Hadronic energy distributions in deep-inelastic electron-proton scattering

This paper presents energy distributions of the hadronic system produced in neutral-current electron-proton deep-inelastic scattering at a centre of mass energy of 296 GeV. Comparison of the results with QCD Monte Carlo models shows that QCD radiation has a strong influence on the characteristics of the final state. The data are reasonably reproduced by the Lund model based on a matrix element calculation in first order ofα s , followed by appropriate parton showers, as well as by the colour dipole model. The HERWIG parton shower model also gives a reasonable representation of the data. Neither the first order matrix elements alone nor the Lund parton shower model, without the matrix element calculation, reproduce the data.

Charm and beauty hadroproduction models: QGSMvs. lund

Predictions for charm and beauty production in hadron-hadron collisions are presented in the framework of the Quark-Gluon String Model (QGSM) and of the Lund Model (implemented via the PYTHIA algorithm) in terms of total cross-sections and inclusive spectra of charm and beauty mesons and baryons for different parton structure functions andK-factors. The structure of events with and without heavy-flavour production is also discussed. The features of the two models are exhaustively investigated and compared with each other and with existing experimental data. Predictions are given at the energies of present and future colliders.

Investigation of inclusive production ofK 0 andK * (892)0 mesons inK + A interactions at 11.2 GeV

Inclusive production ofK0 andK* (892)0 mesons inK+A-interactions (A=Be, Cu, Pb) at the energy 11.2 GeV has been investigated to study hadronisation of the leading\(\bar s\)-quark; the results are presented. Double differential cross sections d2σ/dxfdpt2 were measured in the region of incident particle fragmentation (0.4≦xf≦1,pt≦0.5 GeV/c). The experimental data obtained were analysed on the basis of the Lund model FRITIOF and a quark-gluon model that takes into account colour screening and hadron formation length effects. The experimental data confirm the picture of hadronisation of the leading\(\bar s\)-quark developed in the latter model.

Deuterons from 300 GeV proton collisions calculated from the Lund model

We present an alternative approach to describe deuteron production in high energy particle collisions. The phenomenological Lund-model has been used to give the number and momentum distribution of secondary nucleons produced in 300 GeV proton-proton collisions. Deuterons are assumed to be produced in a final state interaction between the nucleons inNN → πd reactions inside a volume of 1 F3. The results are compared to experimental data.

Predictions for secondary particle production at existing and future hadron-hadron colliders

We consider the predictions of the Quark-Gluon String Model (QGSM) and of the Lund Model algorithm (PYTHIA) for the inclusive spectra and multiplicity distributions of different secondary hadrons produced in pp (or\(\bar pp\)) collisions in the energy interval\(\sqrt s = 62 GeV \div 200 TeV\). Both models describe reasonably well the existing experimental data, however their predictions for the case of very high energies are different. We discuss the possible reasons for these differences.

Two-particle correlations and the origin of intermittency in muon-nucleon interactions

The relation between two-particle correlations, in particular the Bose-Einstein effect, and the intermittency signal is investigated in muon-nucleon scattering at 280 GeV using data of the European Muon Collaboration. From a comparison of the second factorial moments for unlike and negative charges with each other and with the predictions of the Lund model it is concluded that the observed intermittent behaviour is due to Bose-Einstein interference.

Pion interferometry and resonances in pp and AA collisions

We study the sensitivity of pion interferometry in pp and pp collisions at ISR energies to the resonance abundance. We show that those data are not compatible with the full resonance fractions predicted by the Lund model. The preliminary S+S and O+Au data at 200 A GeV are, however, not incompatible with the Lund predictions, although their sensitivity to resonances is significantly weaker than in the pp/ pp case.

STRING FRAGMENTATION MODEL AND INCLUSIVE PRODUCTION OF K MESONS

An account of the inclusive production of K mesons in electron-positron annihilation is given. The most recent measurements on the cross section are exhibited and compared with the predictions of the Lund model. The model gives a satisfactory agreement with the experimental data. The results from different experiments on cross section, the mean multiplicity per multihadronic event and various other characteristics are found to be consistent.

Study of inclusive Lambda production in e+e- annihilations at 29 GeV.

Cross sections are presented for the inclusive production of {Lambda} hyperons in electron-positron annihilations at {radical}{ital s} =29 GeV based on the full 291-pb{sup {minus}1} sample of data taken in the High Resolution Spectrometer experiment at the SLAC {ital e}{sup +}{ital e}{minus} storage ring PEP. These results, and the associated correlation analyses, are consistent with the Lund model predictions with the strange diquark suppression ratio {delta} fixed at 0.59{plus minus}0.10{plus minus}0.18, as compared to the standard Lund value of 0.32. The {Lambda} multiplicity has been found to be 0.182{plus minus}0.020 per event. The opposite-strangeness multiplicity {l angle}{ital n}{sub {Lambda}}{Lambda}{bar a}{r angle} has been measured to be 0.046{plus minus}0.020, whereas the like-strangeness multiplicity {l angle}{ital n}{sub {Lambda}{Lambda}}+{bar {Lambda}}{bar {Lambda}}{r angle} is 0.009{plus minus}0.028. A strong correlation is found between {Lambda}'s and {bar {Lambda}} 's; when one is found in an event, the other is found in the same event with a probability that exceeds 50%.

Revisiting the Lund model

The author briefly reviews the main features of the Lund model emphasizing its good and (due to space limitations more briefly) its more doubtful properties. Needless to say, this will be a subjective view and his criteria for 'good' and 'bad' are open to objections. A particular problem is that there are several versions of what is called the Lund model on the market. Although the author has the greatest confidence in all his former and present collaborators, who have generally provided these versions, he will describe those features of the model, which are contained in the (default versions of) two Monte Carlo simulation programs ARIADNE (present version 3.1) and JETSET (present version 7.2). He, nevertheless, hopes to convince you that the model contains dynamics and not only 'black box' Monte Carlo simulations! He, when the occasion arises, makes connections with other schemes.

String Fragmentation Model and Inclusive Production of K*±(892)11The project supported by the Pakistan Science Foundation under Contract No. P-PU-Phys. (60)

An account of the inclusive production of K*±(892) in electron-positron annihilation is given. The most recent measurements on the cross section are exhibited and compared with the predictions of version 6.3 of the Lund model. A satisfactory agreement is obtained. The results on mean multiplicity per multihadronic event from CELLO, PEP and PETRA collaborations are found to be consistent.

Study of the energy flow in sulphur-and oxygen-nucleus collisions at 60 and 200 GeV/nucleon

We report on a systematic study of midrapidity transverse energy production and forward energy flow in interactions of16O and32S projectiles with S, Cu, Ag and Au targets at 60 and 200 GeV/nucleon. The variation of the shape of theET distributions with target and projectile mass can be understood from collision geometry. AverageET values determined for central collisions show an increasing stopping power for heavier target nuclei. A higher relative stopping is observed at 60 GeV/nucleon than at 200 GeV/nucleon. Bjorken estimates of the energy density reach approximately 3 GeV/fm3 in highET events at 200 GeV/nucleon with16O and32S projectiles. The systematics of the data and the shapes ofET and pseudorapidity distributions are well described by the Lund model Fritiof.

Gamma production in p 20Ne and pN interactions at 300 GeV.

Data on the multiplicity and inclusive spectra of $\ensuremath{\gamma}$ produced in inelastic $p^{20}\mathrm{Ne}$ and $\mathrm{pN}$ interactions at 300 GeV are presented. The $\ensuremath{\gamma}$ multiplicity for $p^{20}\mathrm{Ne}$ interactions is 11.43\ifmmode\pm\else\textpm\fi{}0.23, and the ratio of $〈{n}_{\ensuremath{\gamma}}〉$ for $p^{20}\mathrm{Ne}$ and $\mathrm{pN}$ interactions is 1.48\ifmmode\pm\else\textpm\fi{}0.05. From an analysis of the effective-mass distributions, $〈{n}_{{\ensuremath{\pi}}^{0}}〉=4.91\ifmmode\pm\else\textpm\fi{}0.52$ and $〈{n}_{{\ensuremath{\eta}}^{0}}〉=1.47\ifmmode\pm\else\textpm\fi{}0.33$. In fact, ${\ensuremath{\eta}}^{0}$ production is much higher in $p^{20}\mathrm{Ne}$ interactions [$R(\frac{{\ensuremath{\eta}}^{0}}{{\ensuremath{\pi}}^{0}})=0.66\ifmmode\pm\else\textpm\fi{}0.12$ for ${n}_{p}\ensuremath{\ge}21$] than in $\mathrm{pN}$ interactions [$R(\frac{{\ensuremath{\eta}}^{0}}{{\ensuremath{\pi}}^{0}})=0.06\ifmmode\pm\else\textpm\fi{}0.04$]. No ${\ensuremath{\eta}}^{\ensuremath{'}}(958)$ signal is seen. Strong correlations between $〈{n}_{\ensuremath{\gamma}}〉$ and ${n}_{p}$, the number of secondary protons, are observed, primarily from the central and target fragmentation regions. Inclusive ${y}^{*}$ and ${p}_{\ensuremath{\perp}}$ spectra are analyzed and evidence for low-energy cascading and rescattering of fast particles in the projectile fragmentation region is discussed. The data are compared to the predictions of the additive quark model, the Lund model, and the dual parton model.

Neutral-strange-particle production in p 20Ne and pN interactions at 300 GeV.

Data on multiplicity, correlations, and inclusive spectra of ${K}_{S}^{0}$ mesons and ${\ensuremath{\Lambda}}^{0}({\overline{\ensuremath{\Lambda}}}^{0})$ hyperons produced with ${x}_{F}\ensuremath{\le}0$ in inelastic $p^{20}\mathrm{Ne}$ and $\mathrm{pN}$ interactions at 300 GeV are presented and compared. The inclusive cross sections for $p^{20}\mathrm{Ne}$ ($\mathrm{pN}$) with ${x}_{F}\ensuremath{\le}0$ are 61.1\ifmmode\pm\else\textpm\fi{}2.8 mb (3.34\ifmmode\pm\else\textpm\fi{}0.64 mb) for ${K}_{S}^{0}$, 40.8\ifmmode\pm\else\textpm\fi{}2.5 mb (1.89\ifmmode\pm\else\textpm\fi{}0.29 mb) for ${\ensuremath{\Lambda}}^{0}$, and 3.9\ifmmode\pm\else\textpm\fi{}0.5 mb (0.31\ifmmode\pm\else\textpm\fi{}0.08 mb) for ${\overline{\ensuremath{\Lambda}}}^{0}$. The multiplicity ratio for $p^{20}\mathrm{Ne}$ and $\mathrm{pN}$ interactions is 1.58\ifmmode\pm\else\textpm\fi{}0.16 for ${K}_{S}^{0}$, 1.95\ifmmode\pm\else\textpm\fi{}0.23 for ${\ensuremath{\Lambda}}^{0}$, and 1.12\ifmmode\pm\else\textpm\fi{}0.43 for ${\overline{\ensuremath{\Lambda}}}^{0}$. We have observed the ${\ensuremath{\Sigma}}^{0}(1193)$ hyperon and measured the average multiplicity (${n}_{{\ensuremath{\Sigma}}^{0}}=0.049\ifmmode\pm\else\textpm\fi{}0.027$) for ${x}_{F}\ensuremath{\le}0$. We have also observed the strange resonances ${K}^{*}(892)$, ${K}^{*}(1415)$, and ${\ensuremath{\Sigma}}^{*}(1385)$ with ${x}_{F}\ensuremath{\le}0$ and measured the fraction of ${V}^{0}$ coming from each resonance. ${\ensuremath{\Lambda}}^{0}$ polarization for ${x}_{F}\ensuremath{\le}0$ is measured and shows a decrease as ${p}_{\ensuremath{\perp}}$ increases [${p}_{\ensuremath{\Lambda}}(p^{20}\mathrm{Ne})\ensuremath{\approx}\ensuremath{-}0.25$ at ${p}_{\ensuremath{\perp}}=1.5$ GeV/c], in agreement with other experiments which measure polarization in the region ${x}_{F}\ensuremath{\gg}0$. Since (43\ifmmode\pm\else\textpm\fi{}7)% of the ${\ensuremath{\Lambda}}^{0}$ are produced in ${\ensuremath{\Sigma}}^{0}\ensuremath{\rightarrow}{\ensuremath{\Lambda}}^{0}\ensuremath{\gamma}$ decays, the ${\ensuremath{\Lambda}}^{0}$ polarization is significantly greater than the measured values. Experimental results are compared to predictions of the Lund model and the dual parton model of soft hadron-nucleus and hadron-nucleon interactions.

Formation time of multiparticle systems in the string model.

Distribution of the formation lengths of a multihadron system is calculated in the framework of the string model of particle production. The general formula and the particular solution for a simple fragmentation function of the Lund model are given. The distribution is used to calculate nuclear attenuation of a two-hadron system.

Inclusive ρ0(770) meson production invp and $$\bar vp$$ charged current interactions

Using data obtained with the bubble chamber BEBC at CERN, the inclusive ρ0 (770) meson production in νp and $$\bar vp$$ charged current reactions is studied. The average ρ0 multiplicity is measured as a function of the event variablesE ν ,W 2,Q 2,x Bj , and the charged multiplicity. The differentialx F ,y *,z andp 2 distributions of the ρ0 are presented as well as the averagep 2 as a function ofW 2 andx F . The ρ0/π0 ratio and the fractions of the π± originating from ρ0 decays are given as functions ofx F . The results are compared to the predictions of fragmentation models. A particular version of the Lund model predicts ρ0 multiplicities which are generally too high, although it qualitatively reproduces many aspects of the data. The ρ0 multiplicities predicted by a semi-empirical model (Wells model) are in quantitative agreement with the measurements.

Contribution of the EMU-01-collaboration to the research for a Quark Gluon Plasma (QGP)

Results from experiments on high energy nucleus-nucleus collisions in emulsion are reviewed in comparison with the Lund model FRITIOF. Correlations between different properties of the colliding particles are discussed.

Inclusive D∗± production in photon-photon collisions

Abstract The TPC/Two-Gamma Collaboration has measured the inclusive cross section for production of charmed D∗± mesons in photon-photon collisions. The reaction utilized was e+e-→e+e-D∗±X, with D∗±→DOπ+-, DO→K-+π ±, and either zero or one outgoing e± detected. The result, σ(e + e - → e + e - D ∗± X) = 74±26±19 pb , is in agreement with the quark parton mo del prediction for e+e- → e+e-c c , combined with a Lund model for the hadronization of the charmed quarks.