Search

Production of strange mesons and baryons is studied in a Monte Carlo Dual Parton model for hadron-hadron, hadron-nucleus and nucleus-nucleus collisions with standard strangeness suppression in the chain fragmentation and enhanced strangeness (up to a SU(3) symmetric sea) at the sea chain ends. Additionally, (qq)-( q q ) production from the sea has been introduced into the chain formation process with the same probability as for the q → qq branching within the chain fragmentation. Rapidity distributions and multiplicity ratios are in reasonable agreement with recent experimental data.

The possibility of string fusion in the dual parton model is studied using the Monte Carlo code DTUJET. It is shown that the introduction of these interactions among strings can explain the large rise of the average transverse momentum of p at high multiplicity seen at Fermilab, without spoiling the agreement of the model with the rest of the observables. Also, an increase of the ratio Λ/π at high multiplicity is produced. The strong interaction of strings can be regarded as an interplay between independent fragmentation of strings and the formation of a quark-gluon plasma.

We study the implications of QCD-weak interference terms on vector boson peaks in two-jet and single-jet cross sections and spin asymmetries in unpolarized and polarized pp and p p collisions at collider energies. It is found that the interference terms strongly influence the cross section: The vector boson peaks in the pp cross sections and parity-violating asymmetries disappear below the interference terms at lower energies. In p p collisions, however, the vector boson peaks survive and measurements of parity-violating spin asymmetries in double- and single-jet cross sections should lead to clear and detectable signals for the vector bosons.

For deep inelastic lepton-hadron scattering we deduce from QCD perturbation theory the cross sections d σ d T and d σ d S in terms of the collective jet variables thrust T and spherocity S. We find that the shape of these cross sections depends mainly on the total hadronic energy W. While present data are consistent with the cross sections calculated they do not yet prove or disprove the presence of three-jet contributions. We predict that these contributions will be clearly visible for W ≳ 12 to 15 GeV.

Semiinclusive two-particle correlations are calculated in the independent cluster emission model. The resulting semi-inclusive correlation functions ϱ 2 n ( y 1 = y 2 = 0) agree rather than well experimental data, esp. with respect to the multiplicity dependence. The average number of charged particles per cluster found from comparison with semiinclusive data is 2.5 charged particles per cluster, a value found earlier also from analysis of inclusive correlations.

ISR data on two-particle rapidity correlations in the region y1 ≈ y2 can be understood in terms of the multiperipheral fireball model and indicate an energy independent upper limit of the average fireball mass. The diffractive contribution to the fireball production leads to characteristic shapes of long range correlations. Data on long range rapidity correlations may be used to determine the fractions of non-diffractive and diffractive one- and two-fireball production.

Using the multi-Regge model we calculate the velocity weight function U(λ) which approximately agrees with the empirically determined function F(λ) of the thermodynamical model at energies between 10 and 30 GeV c except near λ = 0. Negatively charged particle spectra are represented well at 19.2 GeV c . U(λ) depends weakly an the primary energy as compared to the energy independence of F(λ). Presently it is not clear how this energy dependence will change if more multi-Regge graphs are included in the calculation of U(λ).

Inclusive two particle spectra and correlation functions are calculated from a multiperipheralthermodynamic model. This model was previously proposed by the authors in order to derive the velocity weight function used in the thermodynamic description of single particle spectra from the multi Regge model. It was argued that the one-fireball graph dominates at accelerator energies. In this model two particle correlation functions are calculated without introducing new concepts or parameters. The results of the calculation are compared with recent data on inclusive π - π - production in K + p collisions at 12 GeV/ c . Good agreement is found with the experimental correlation function plotted in terms of the rapidity difference Δy ∗ = y 1 ∗ −y 2 ∗ of the two observed negative π mesons.

The cluster model with Bose effect explaines rather well recent FNAL data on (Δy, Δφ) correlations at Δy = Δφ = 0 of identical particles. To test this interpretation more in detail we propose transverse momentum limitations which should enhance the effect. It is pointed out that the conventional cluster analysis of Δy correlation data is only justified with data around Δφ = π.

The difference of the short range effect observed in azimuthal correlations of like and unlike particle pairs is interpreted as due to an identical and unidentical boson effect, resp., in the decay of clusters produced in the central region of hadron hadron collisions.

The recently observed rise of the e/ π ratio at small transverse momentum in pp collisions can be understood in a model with continuum hadronic vector states which decay into di-leptons. The mass and momentum distribution of the continuum hadronic states—which we derive from the distribution of produced quarks—is consistent with the distribution of hadronic clusters as determined from multi hadron correlation studies.

Cross sections are given for the scattering of polarized quarks and antiquarks according to lowest-order QCD perturbation theory. Non-vanishing spin asymmetries lead to observable effects for large-p⊥ hadron production in collisions of polarized hadrons, which are proposed as a test of the relevance of the QCD picture for large-p⊥ reactions.

Relying on the QCD based hard scattering formalism we estimate cross sections and spin asymmetries for large-pt jet production from 2ϰ processes in collisions of electrons and positrons of definite helicity states.

Lattice versions with restricted supersymmetry of simple (1+1)-dimensional supersymmetric models are numerically studied using a local hamiltonian Monte Carlo method. The pattern of supersymmetry breaking closely follows the expectations of Bartels and Bronzan obtained in an alternative lattice formulation.

The massive Schwinger model with two flavours is studied using the local hamiltonian lattice Monte Carlo method. Chiral symmetry breaking is studied using the fermion condensate as order parameter. For a small ratio of the two fermion masses, degeneracy of the two flavours is found. For a large ratio of the masses, the heavy flavour decouples and the light fermion behaves like in the one flavour Schwinger model.

We modify a previously developed multi-string model for particle production to include the primordial transverse momentum of the partons in the incoming hadrons. Rapidity spectra, correlations and multiplicity distributions are unsensitive to the modification. The average transverse momentum of secondaries is found to increase with multiplicity, as observed at the SPS collider. However, a rather large parton transverse momentum (1.1–1.4 GeV) is required.

Particle production in nucleus-nucleus collisions is calculated in a Monte Carlo version of the dual multi-chain fragmentation model. The model uses an efficient method to sample the numbers of interactions in nucleus-nucleus collisions. We calculate distributions in the transverse energy and multiplicity and compare with data obtained at the CERN SPS in OPb collisions with 200 GeV per nucleon.

Two essential modifications of the thermodynamic single particle spectra using fireballs according to the strong bootstrap model are described: (i) An energy-dependent velocity weight function is introduced which leads to better agreement with the flat single particle spectra in the central region observed at the ISR. (ii) Heavy pair production is modified by producing the two particles in different steps of the decay chain of the fireballs. The fact that heavy fireballs are produced leads in the model to a natural understanding of the deviations from scaling behaviour in the central region of single particle spectra p + p → π+-, p or K− + anything between 20 GeV and ISR energies. The particle production ratios p /π−, K−/π−, π+/p, K+/p and p /p are compared to recent ISR data.

The scaling behaviour of the thermodynamic particle spectra is studied using the rapidity variable r. Between 20 and 500 GeVc the thermodynamic spectra behave not as expected from the scaling hypothesis. Reasons for this behaviour are discussed. A comparison with recent cosmic ray data indicates that scaling is probably not yet present at accelerator energies. The structure function of the inclusive π+-spectra from p-p-collisions according to the thermodynamic model is calculated for small longitudinal momenta in the laboratory system, and is found already nearly independent on primary proton momentum between 10 and 100 GeVc.

We report a comparison of the thermodynamic model of multiparticle production with experimental data K + p → K o + anything and K − + p → K o + anything at 8.2 and 10.1 GeV c . Using the same velocity weight function F o ( λ ) for through-going particles as determined from inclusive single particle spectra in p - p collisions we find a remarkable agreement of the thermodynamic K o - spectra with data in the fragmentation region and with respect to themissing mass dependence of the momentum transfer distributions. It is furthermore found that with respect to the production of through-going particles the isospin is conserved as locally as baryob number and strangeness. This behaviour explains the observation that the mayority of the K o in the fragmentation region is produced via resonances.

We report about a comparison of the thermodynamical model for multiparticle particle production with new experimental data. Particle yields measured at P o = 19.2 GeV/ c and 70 GeV/ c are first used to correct the behaviour of the thermodynamical model near the kinematical limits. The resulting predictions of the model agree well with new experimental data at 12.5, 35, 43, 52 and 70 GeV/ c .

Angular distributions obtained from the thermodynamic model of multi-particle production are compared with cosmic ray results at 175 GeV/ c and with angular distributions obtained according to parametrizations with Feynman like scaling behaviour.

With reference to a recent paper of the Bombay-CERN-Cracow collaboration, we show that the ISR emulsion experiment does not disprove scaling.

Heavy J particles decaying into e + e − were recently found in p-Be collisions [1] as well as in e + e − annihilations [2, 3], where also the decay into hadrons with a branching ratio of about σ( J → h ) σ( J → e + e − ) = 15 was observed.