Lund Model Research Articles

Production of η mesons in e +e − annihilations at √ s=29 GeV

Data from e +e − annihilations at 29 GeV have been used to measure the production cross section and fragmentation function of η mesons. The signal is observed in the η→ γγ decay channel. The fragmentation for p η >1.5 GeV/ c agrees well with the prediction of the Lund model, whereas the prediction of the Webber model lies above the data. The mean multiplicity is measured to be 〈 n η 〉=0.58±0.10 η mesons per hadronic event, of which 0.51 represents the direct production of η and η′ mesons in the fragmentation chain.

Review of high energy heavy ion reactions in emulsion

Results from experiments on high energy nucleus-nucleus collisions in emulsion are reviewed. Comparisons with hadron-nucleus collisions and with the Lund model FRITIOF for nucleus-nucleus collisions are presented. Correlation between hadronization and nuclear fragmentation is discussed.

Comparison between hadronic final states produced in μp ande + e − interactions

A comparison is made between the properties of the final state hadrons produced in 280 GeV μp interactions and ine+e− annihilation. The Lund model of hadroproduction is used as an aid in understanding the differences observed. The hadron distributions from μp ande+e− interactions are consistent with the quark parton model assumption of environmental independence, provided that the differences in heavy quark production and hard QCD effects in the two processes are taken into account. A comparison with aK+p experiment is also made. Values are also determined for the Lund model parameters σq = 0.410 ± 0.002 ± 0.020 GeV and σ′ = 0.29 −0.15 −0.13 +0.09+0.10 GeV, controlling the transverse momenta in fragmentation and intrinsic transverse momenta of the struck quark respectively.

Rho and omega production in pi+p interactions at 15.7 GeV/c.

We report the results of a study of \ensuremath{\rho} and \ensuremath{\omega} production in ${\ensuremath{\pi}}^{+}$p interactions at 15.7 GeV/c. The SLAC hybrid bubble-chamber facility was used to study reactions in which neutral particles are produced. Three tantalum plates inside the 40-in. bubble chamber and a large array of lead glass downstream of the chamber provided photon detection over a large solid angle. Final states with two neutral particles have been isolated with kinematic fits in which neutral pions were reconstructed in the plates and lead glass. Data from an earlier untriggered ${\ensuremath{\pi}}^{+}$p bubble-chamber experiment at 15 GeV/c were used to obtain samples of events in channels which did not trigger the hybrid system. Cross sections for \ensuremath{\rho} and \ensuremath{\omega} production are given for several exclusive final states. Relative \ensuremath{\rho} and \ensuremath{\omega} production rates are studied. The ratio of nondiffractive \ensuremath{\omega} to ${\ensuremath{\rho}}^{0}$ production is measured to be \ensuremath{\omega}/${\ensuremath{\rho}}^{0}$=0.44\ifmmode\pm\else\textpm\fi{}0.07. We estimate the inclusive \ensuremath{\omega} cross section to be 1.9\ifmmode\pm\else\textpm\fi{}0.3 mb. The results are compared to the Lund model of low-${p}_{T}$ hadronic reactions.

Analysis of transverse momentum distributions forpp interactions at 360 GeV/c in the framework of a quark-diquark fragmentation model

Using a quark-diquark fragmentation model, in which either the Field-Feynman or the Lund model is coupled with a quark-diquark distribution function, we study transverse momentum distributions,p T, for the inclusive reactionspp→hadron +anything at 360 GeV/c. We find that a primordial mean transverse momentum 〈k T〉≃0.4 GeV/c can well reproduce thep T 2 distributions of charged hadrons, π0,K s 0 , Λ0,K * and Σ* and the Feynmanx−p T correlations. We confirm that a diquark in a proton plays an important role in reproducing thex−p T correlation of Λ0.

Jet production and fragmentation properties in deep inelastic muon scattering

Results are presented from a study of deep inelastic 280 GeV muon-nucleon interactions on the transverse momenta and jet properties of the final state hadrons. The results are analysed in a way which attempts to separate the contributions of hard and soft QCD effects from those that arise from the fragmentation process. The fragmentation models with which the data are compared are the Lund string model, the independent jet model, the QCD parton shower model including soft gluon interference effects, and the firestring model. The discrimination between these models is discussed. Various methods of analysis of the data in terms of hard QCD processes are presented. From a study of the properties of the jet profiles a value of αs, to leading order, is determined using the Lund string model, namely αs=0.29±0.01 (stat.) ±0.02 (syst.), forQ2∼20 GeV2.

Production of strange baryons in e+e- annihilations at 29 GeV.

The production of strange baryons ..sigma../sup +- / (1385) and ..gamma../sup -/ has been observed in e/sup +/e/sup -/ annihilations at 29 GeV center-of-mass energy, by use of data obtained with the High Resolution Spectrometer at the SLAC storage ring PEP. The total mean multiplicities are measured to be = 0.033 +- 0.006 +- 0.005 and = 0.016 +- 0.004 +- 0.004 per hadronic event. The results are in good agreement with the Lund string model.

The Lund model

The Lund model, inspired by quantum chromodynamics, has provided a very promising approach to the dynamics of quark and gluon interactions. Starting with a brief reprise of basic concepts in relativity, quantum mechanics of fields and particle physics, this 1998 book discusses: the dynamics of the massless relativistic string; confinement; causality and relativistic covariance; Lund fragmentation processes; QED and QCD Bremsstrahlung; multiplicities and particle-parton distributions. Throughout the book, theory is confronted with current experimental data, and implications for future experiments are also considered. The book also explores the relationships between the Lund model and other models based on field theory (the Schwinger model, S-matrix models, light-cone algebra physics and variations of the parton model), and models based on statistical mechanics (the Feynman-Wilson gas, scaling, iterative cascade models).

Lund model and an outside-inside aspect of the inside-outside cascade

The formation zone of high-energy hadrons is discussed based on the Lund model of hadronization. The ambiguity in the concept of formation length for composite particles is pointed out. Two different formation lengths are defined and their distributions calculated. The results are compared with the data on fragmentation of 30 GeV pions into protons and antiprotons. The data indicate the possibility of an outside-inside cascade picture of hadronization in the projectile fragmentation region.

Relativistic Heavy Ion Reactions

Relativistic heavy ion reactions are reviewed in terms of our present understanding of some selected experimental results from the LBL Bevalac and the CERN ISR. The Lund Model for nucleus-nucleus collisions is presented and its power of predictivity is illustrated.

ON THE DEPENDENCE BETWEEN HADRONIZATION AND NUCLEAR FRAGMENTATION IN HADRON INDUCED REACTIONS

Results from experiments on hadronic interactions with emulsion nuclei at different energies are compared with calculations from the Lund model for interactions between hadrons and nuclei. Special emphasis is put on the correlation between the hadronization and nuclear fragmentation. The model is able to describe many of the experimentally observed features, as shown by several examples.

Hadronic ? production and the lund model for lowp T interactions

Experimental results on inclusive ϕ production are compared with the Lund model for lowp T hadronic interactions. The data is based on a sample of 600,000 ϕ mesons in the kinematic rangep T <1.0 (GeV/c)2 and 0.0<xF<0.4, produced in π±,K±,p and\(\bar p\) Be interactions at 100 GeV/c and 120 GeV/c incident momentum. The Lund model reproduces the shapes of the longitudinal differential cross sections reasonably well, but the relative cross sections for incident, π,K andp show a discrepancy with the data.

Joint production of ? mesons and? �,? 0,p, $$\bar p$$ ,K s 0 andK � in hadronic interactions

The joint production of ϕ mesons andπ±,π0,p,\(\bar p\),Ks0 andK± is investigated using a sample of 600,000 inclusive ϕ meson events obtained in hadron Be interactions with incidentπ±,p,\(\bar p\) andK± beams. Evidence is presented for the joint production of ϕ mesons and strange particles produced with non-strange incident beams. With incidentK± beam the number of additional strange particles is suppressed. The results are found to be in agreement with the qualitative predictions of a parton fusion model. The comparison with the Lund model for lowpT processes is fair.

Some tests of fragmentation models in exclusive channels inK − p reactions at 32 GeV/c

Experimental data for exclusive channels of multiplicity 4–8 in 32 GeV/cK−p reactions are compared with predictions of the Lund model. This leads to the following insights: — Evidence is obtained for azimuthal correlations betweenK+K− pairs and p pairs supporting the Lund fragmenttation scheme. — The disagreement of the observed behaviour of leading protons andK− with the model predictions indicates that the fate of the valence quarks is not well described by the model. The data support the idea of valence quark separation as advocated by dual models.

Lambda production in e+e- annihilations at 29 GeV: Comparison with Lund-model predictions.

This paper presents measurements of the inclusive production cross sections of ..lambda.. baryons in e/sup +/e/sup -/ annihilations at ..sqrt..s = 29 GeV. The data sample corresponds to an integrated luminosity of 256 pb/sup -1/ collected with the High-Resolution Spectrometer at the SLAC storage ring PEP. Comparisons are made to the predictions of the Lund model. The data are well described with use of a strange diquark suppression parameter, (us/ud)/(s/d), of 0.89 +- 0.10/sub -0.16//sup +0.56/, and the measured ..lambda../sub c/..--> lambda..+X branching ratio of (23 +- 10%).

Nuclear stopping power in ?? anddd collisions

Inelasticαα anddd collisions were studied at a centre-of-mass energy √S NN=31.2 GeV per nucleon-nucleon collision, using the Split-Field Magnet (SFM) detector at the CERN ISR. In this paper we show the inclusive and semi-inclusive rapidity distributions of protons, compare them with predictions of the Lund model, and calculate the average rapidity loss for participant protons. From the negative particles we calculate the inelasticity of the interaction, the average energy per particle, and the degree of isotropy of the produced hadrons.

Inclusive charged particle production near the kinematic limit in e +e − annihilation at 29 GeV

Inclusive production of charged particles has been studied in e +e − annihilation at s s=29 GeV using the high resolution spectrometer at PEP. Differential cross sections are presented in the range of scaled energy 0.1< z<1.0. The data for z<0.5 show the (1− z) 2 behavior predicted by the dimensional counting rules. Comparisons are made with predictions of the Lund string model and the Webber cluster model.

Neutral K ∗(890) and ρ 0 meson production in e +e − annihilation at [formula omitted

The production of neutral K ∗(890) and ρ 0 mesons was studied in e +e − annihilation at s =29 GeV using the High Resolution Spectrometer at PEP. Differential cross sections are presented as a function of the scaled energy variable z and compared to π 0 and K 0 production. The measured multiplicities are 0.84±0.08 ϱ 0 mesons and 0.57±0.09 K ∗0(890) mesons per event for a meson momentum greater than 725 MeV/ c. The ratios of vector meson to pseudoscalar meson production for (u,d), s and c quark are compared to predictions of the Lund model.

Comparison of three-jet events with QCD shower models

Distributions of particles in three-jet events from e +e − → hadrons are compared with different fragmentation schemes, i.e. the Lund string model, independent parton fragmentation and QCD shower models. Effects specific to the string scheme, which have been seen in the data, are also reproduced by QCD shower models if soft gluon interference effects are included.

Measurement of energy-energy correlations in e+e--->hadrons at sqrt s =29 GeV.

The energy-energy correlation cross section for hadrons produced in electron-positron annihilation at a center-of-mass energy of 29 GeV has been measured with the MAC detector at SLAC. The result is corrected for the effects of detector resolution, acceptance, and initial-state radiation. The correlation is measured in two independent ways on the same data sample: the energy weights and angles are obtained either from the energy flow in the finely segmented total absorption calorimeters or from the momenta of charged tracks in the central drift chamber. This procedure helps reduce systematic errors by cross-checking the effects of the detector on the measurement, particularly important because the corrections depend on complex Monte Carlo simulations. The results are compared with the predictions of Monte Carlo models of complete second-order perturbative quantum chromodynamics and fragmentation, with the following conclusions: (1) fitting the asymmetry for large correlation angles gives values for ..cap alpha../sub S/ of 0.120 +- 0.006 in perturbation theory, 0.185 +- 0.013 in the Lund string model, and values which vary from 0.105 to 0.140 ( +- 0.01) in the incoherent jet models, depending on the gluon fragmentation scheme and the algorithm used for momentum conservation; and (2) the string fragmentation model providesmore » a satisfactory description of the measured energy-energy correlation cross section, whereas incoherent jet formation does not.« less