abstract

The results of \(\bar p p\)-annihilation measurements with Crystal Barrel detector are presented. Light meson spectroscopy is stressed. The evidence for exotic states like Glue-Balls or Hybrids is shown.

abstract

Data on antiproton–proton annihilation at rest into two mesons are presented with special emphasis on the importance of dynamical selection rules. These selection rules reduce the frequency of some annihilation rates for otherwise allowed annihilation modes by one order of magnitude. It is shown that SU(3) breaking cannot be held responsible for such large effects. This fact motivates an analysis of \(\bar p p\) branching ratios by SU(3) amplitudes. Different SU(3) coupling schemes and their interpretation are presented. A coupling scheme tracing the quark flux from the initial to the final state gives the best interpretation of the data and of the dynamical selection rules.

abstract

Some aspects of axial charge and current in pion production and absorption are reviewed. In addition to recent new mechanisms proposed to explain threshold \(pp \to pp\pi ^0\), the role of the \({\mit \Delta }\)(1232) isobar is reiterated also in the two-nucleon axial charge.

abstract

We report on the current status of the search for the \(\pi \)NN resonance \(d^{\prime }\) with I(J\(^{\rm P}) = 0(0^-)\) and \({\rm M} = 2.06\) GeV in the 2\(\pi \) production in \(pp\) collisions as well as in the pionic double charge exchange.

abstract

The planned experiments for vector meson production near threshold with the DISTO spectrometer at SATURNE are discussed. The first results for the reaction \(pp \to pp{\mit \Phi }\) studied via the \({\mit \Phi } \to K^+ K^-\) decay are presented.

abstract

We investigate the exclusive proton-induced \(K^+\) production near the kaon threshold. Compared are two models: a meson-exchange model, which includes \(\pi \), \(\rho \), \(K\) and \(K^*\) exchange, together with the dominant baryon resonances, and a quark–gluon model, where momentum sharing is provided via the exchange of two gluons. Based on covariant bound state wave functions for the meson and the baryons — which we treat as quark–diquark objects — first results for the \(pp \to p{\mit \Lambda }K^+\) total cross section are presented for both models.

abstract

A partial wave amplitude analysis of \(\bar p p \to \pi ^- \pi ^+\) and \(\bar p p \to K^-K^+\) has been performed for data obtained at LEAR in the range \(p_{\rm lab} = 360\)–1000 MeV/\(c\). For \(\bar p p \to \pi ^- \pi ^+\) partial wave amplitudes with \(J = 0\), 1, 2, and 3 are required, while for \(\bar p p \to K^-K^+\) amplitudes with \(J = 0\), 1, and 2 are sufficient to fit the data in this energy range.

abstract

The \(\pi \)NN dynamics generates a strong and narrow structure in the cross section of three-body processes in the \(I=0\), \(J^P=0^-\) \(\pi NN\) system at mass \(M=2.06\)–2.09 GeV with width 30–50 MeV. The origin is the three-body interaction due to the \(NN^1S_0\) and \(\pi NS_{11}\) interactions in the subsystems.

abstract

The future spin correlation measurements planned for IUCF site require precise target and beam polarization handling. The fine tuning performed recently in IUCF facility is presented and discussed.

abstract

A brief overview on recent model calculations for near threshold pion production in nucleon–nucleon collisions is given. Results from our own investigations of the reactions \(pp \to pp\pi ^0\) and \(pn \to d\pi ^0\) are presented. Direct production, heavy meson exchange and pion rescattering are taken into account. For the latter a T-matrix obtained from a microscopic model of the \(\pi N\) interaction is employed. We obtain a significant contribution from rescattering, but not enough to describe the data for \(pp \to pp\pi ^0\). The missing production rate can be provided by heavy meson exchanges. For the first time the effect of off—shell rescattering is investigated for the reaction \(pn \to d\pi ^0\). Isoscalar rescattering in combination with isovector rescattering is able to describe the s-wave production data. We confirm that heavy meson exchanges are negligible in this reaction.

abstract

First results of the COSY-11 collaboration are presented in this paper. The motivation for the investigation of meson production is discussed. The description of the COSY-11 experimental apparatus, including the method of particle identification and luminosity monitoring will be shown. Preliminary results of first test measurements for the production of (\(\pi ^+\pi ^-\)), \(\eta \), \(\eta \prime \), and (\(K^+K^-\)) mesons in the \(p + p\) interaction will be given. Furthermore, the results of a test for the \(pp \to pK^+{\mit \Lambda }\) reaction is presented.

abstract

The \(pp \to d\pi ^+\) reaction is studied at excess energies between 0.275 MeV and 3.86 MeV. Differential and total cross sections were measured employing a magnetic spectrometer with an acceptance of close to 4\(\pi \) in the center of mass system. From the total cross sections the \(S\) and \(P\)—wave contributions are deduced. The measured anisotropies between 0.008 and 0.29 suggest a non-negligible \(P\)—wave contribution even close to threshold. Compared to existing data the present results offer no evidence for charge-symmetry breaking or time reversal violation.

abstract

The momentum spectrum of \(^4\)He particles from \(d+d\) reactions at \(E_{\rm lab} = 570\) MeV has been measured at zero degrees in the laboratory. The missing-mass spectrum closely follows a pure phase space behaviour for the isospin zero channel of two pions.

abstract

Quasifree \(\eta \)-production in proton–deuteron collisions has been studied using a D\(_2\) internal cluster jet target at the CELSIUS storage ring in Uppsala. By exploiting the Fermi momentum of the target nucleons the excitation functions for the reactions \(pp \to pp\eta \), \(pn \to pn\eta \) and \(pn \to d\eta \) could be measured staying at a fixed proton beam energy of 1.35 GeV. Preliminary results for excess energies in the centre of mass from 15 to 115 MeV are reported.

abstract

The reaction \(pd \to ^3\)He \(\pi ^+\pi ^-\) was measured at 1150 MeV/\(c\) proton beam momentum using MOMO instalation at COSY.

abstract

Selected results of the meson production study in the \(\vec p + d \to ^3\)He \(+ X\) reaction realized with the SPES 3 spectrometer at SATURNE will be presented and related to a semiphenomenological three nucleon model.

abstract

First results of measurements with the Time of Flight spectrometer are shown. Reconstructed missing mass distributions of the reactions \(pp \to d\pi ^+\), \(pp \to pp\pi ^0\), and \(pp \to pK^+{\mit \Lambda }\) are given.

abstract

Detection of dilepton decay of vector mesons by means of HADES installation is discussed.

abstract

Recent experimental data for the reaction \(pd \to pd\pi ^0\) in the pion momentum range \(\eta = p^{\pi ^0}_{\rm c.m.max}/m_{\pi ^0}c \leq 0.96\) is discussed. The excitation function \(\sigma _{pd\pi ^0}(T_p)\) roughly follows a \(\eta ^4\) power law for Ss wave interaction; close to threshold it is compatible with that for \(pd \to ^3\)He\(\pi ^0\), i.e. a strong spin-dublett interaction. The model of a quasi-free elementary process \(np \to d\pi ^0\) with a spectator proton describes \(\sigma _{pd\pi ^0}(Tp)\), too, but does not exhaust the observed spectator energy spectra. Comparison to isospin related \(pd \to nd\pi ^+\) data indicates another reaction mechanism contributing with a strength comparable to that of the quasi-free process.

abstract

The data collected by Dubna–Warsaw–Kosice–Moscow–Strasburg Collaboration at the Dubna proton accelerator on double pion production are presented.

abstract

It is shown that the two-step model of the reaction \(pd \to ^3\)He \(X\) \((X = \eta , \eta ^\prime , \omega , \phi )\), involving the subprocesses \(pp \to d\pi ^+\) and \(\pi ^+n \to Xp\) allows to explain the form of energy dependence of experimental cross sections above the thresholds under assumption that the singlet part of the \(pp \to d\pi ^+\) amplitude dominates in collinear kinematics. The spin–spin asymmetry for the reaction \(\vec d \vec p \to ^3\)He \(X\) has been found to be \(\sim -1\) in the forward-backward approximation.

abstract

A phenomenological model is used to analyze the \(\pi \) and \(\eta \) meson formation in \(pp\) collisions. The aim is to describe final state interactions. Strong \(\eta pp\) correlations are found at very low energies.

abstract

The reactions \(pd \to \eta + X\) have been measured at four beam energies: 930, 965, 1037 and 1100 MeV. The reactions were identified by detecting charged particles in plastic scintillator detectors and the \(\eta \) photons in two arrays of CsI(Na) crystals. A preliminary estimation of the cross section of the \(^3\)He\(\eta \) channel has been made. It is in agreement with previous measurements done at lower energies.

abstract

Subthreshold kaon production has been measured in symmetric nucleus–nucleus collisions as a function of the nuclear mass, the beam energy and the collision centrality. In Au + Au collisions at 1 \(A\)GeV the \(K^+\) multiplicity increases more than linearly with increasing number of participating nucleons. Transport calculations have to assume a soft equation of state in order to reproduce our data. The in-medium \(K^-\) cross section measured in Ni + Ni collisions is enhanced by a factor of about 7 as compared to the free cross section when using the \(K^+\) cross section at equivalent beam energies as a normalization.

abstract

Charged pion production is studied at different energies in two systems, Ni + Ni and Au + Au, using the FOPI detector at GSI. The pion production probability is found to be reduced for the heavier system. The rescattering of pions from spectator matter is observed under all conditions, it is responsible for the non-thermal shape of the rapidity spectra. The excited Baryon resonances are shown to be a major source of the observed pions, higher resonances than the \({\mit \Delta }\)(1232) are responsible for pions with large transverse momenta.

abstract

\(K^+\) production on carbon and lead was measured for proton beam kinetic energies from 1.2 up to 2.5 GeV. It was found that the high momentum tail of the kaon spectrum extends beyond the kinematical limit for the elementary reaction. The influence of the internal motion of nucleons on the particle production was studied within the folding model.

abstract

Measurements and theoretical analyses of asymmetries from pion-nucleus scattering and pion-induced single-charge exchange reactions on polarized spin-1/2 nuclei are reviewed.

abstract

The (\(^3\)He, t) charge exchange reaction at 2. GeV incident energy with the new setup SPES IV-\(\pi \) has been realized in December 1995 and March 1996, in order to study the coherent production process of pions. This setup allows to isolate the ground state of the target nucleus, and to sign this process without ambiguity. We give some preliminary results in target excitation energy and transferred energy.

abstract

The utilization of the slow ramping mode at the CELSIUS storage ring to perform excitation function experiments is discussed. New results on pion production from the international CHIC collaboration are presented.

abstract

The \(K^+\) differential cross sections are evaluated in the simple and extended folding model. Angular dependence of the cross sections is compared with existing experimental data.

abstract

The new results on the inclusive double charge exchange (DCX) reaction \(^{16}\)O\((\pi ^-,\pi ^+)X\) at incident kinetic energy \(T_0 = 0.75\) and 1.15 GeV are presented. The data were taken without using Cherenkov counters. The new DCX cross sections agree well with the old ones. Both the values are about an order of magnitude larger than the theoretical cross section calculated for the standard sequential mechanism. Two other approaches which seem to explain the discrepancy are also briefly reviewed.

abstract

We measured \(\eta \) and \(\pi ^0\) meson production in nucleus–nucleus reaction at beam energy below the free nucleon–nucleon pion creation threshold. Preliminary results indicate that the scaling on the transverse mass between \(\pi \)’s and \(\eta \)‘s is still valid at very low energies. Meson cross sections can be understood in terms of thermal population of the baryonic resonances \({\mit \Delta }\)(1232) and \(N^*\)(1535). Also, we observe a statistically-significant correlation for proton-\(\pi ^0\) coincidences, which we assign to the strength distribution of the \({\mit \Delta }\) baryonic resonance. The same analysis shows no correlation in the case of deuteron-\(\pi ^0\) coincidences.

abstract

The report is presented about first results on measurements of hypernuclei produced by the internal proton beam on uranium target.

abstract

A concise description of the experiments that make up the CHAOS program at TRIUMF site is presented.

abstract

A parton model analysis was made of the kaon production data at 3.65 GeV/nucleon for collision of deutrons and carbon ions with carbon and lead target. The enhancement of kaon production could be accounted for the collective correlations in the target nuclei.

abstract

A method to determine the size of the pion emitting source in central collisions from the energy differential \(\pi ^-/\pi ^+\) ratio is proposed. This approach was applied to the experimental results for a medium-mass and a heavy-mass system.

abstract

A major goal of the experimental program with the 0\(^\circ \) Facility ANKE at COSY-Jülich is the investigation of the influence of the nuclear medium on elementary particles and their reactions. In particular, it is planned to study the production of \(K^+\), \(K^-\) and \(\phi \) mesons in proton–nucleus interactions close to and below the NN thresholds.

abstract

A High Acceptance DiElectron Spectrometer (HADES) has been proposed for the SIS accelerator at GSI in order to measure \(e^+e^-\) pairs produced in proton, meson and heavy ion induced collisions. HADES will be able to operate at the highest luminosities available at SIS in an environment of high hadron and photon background. The physics program includes studies of in-medium properties of vector mesons and electromagnetic form factors of hadrons. A Ring Imaging Cerenkov Counter (RICH) and arrays of pre-shower detectors and TOF wall serve for electron identification. Particle momentum determination is achieved with a magnetic spectrometer consisting of 6 superconducting coils in toroidal geometry and 2 sets of mini drift chambers for tracking. The detector features have been investigated in detailed simulations. The anticipated mass resolution and geometrical acceptance of the detector amounts to 1% and 40%, respectively for pairs from \(\rho /\omega \) decay. First experiments are planned for 1998.

abstract

The purpose of the PHOBOS experiment is to study the physics of heavy ion collisions at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory. The PHOBOS detector is designed and optimized for detailed measurements of various experimental observables which may signal the onset of new phenomena expected in central collisions of gold nuclei at the center-of-mass energy of 200 GeV/nucleon. In particular, a comprehensive study of hadrons and photons produced in such collisions should reveal the existence and properties of a new phase of matter, the Quark-Gluon Plasma, which is predicted to be formed at high energy densities. In this paper a short overview of the PHOBOS apparatus and its measurement capabilities is presented.

abstract

The history of \(\pi ^0\) photoproduction near threshold on the proton and recent results of \(\pi ^0\) electroproduction are discussed, including a comparison with recent calculations in Chiral Perturbation Theory. Then an experiment on coherent \(\pi ^0\) production on \(^4\)He in the \({\mit \Delta }\) region, in which \({\mit \Delta }\) propagation through a nucleus and a two-body mechanism of pion production will be studied, is described. A special detector is developed for the detection of the recoiling \(^4\)He nuclei.

abstract

The electromagnetic structure of the nucleon is of fundamental importance to our understanding of models of the nucleon and of nuclei. Experiments which extract information on spin degrees of freedom can enhance knowledge of small components of the nucleon and nuclear wave functions. This review summarizes the results of recent experiments which exploit measurements of spin observables.

abstract

The results from a series of experiments investigating \(\pi ^0\)- and \(\eta \)-photoproduction are summarized. They were carried out with the TAPS detector at the Mainz MAMI accelerator. The p(\(\gamma ,\eta \))p reaction was used to study the excitation of the \(S_{11}\)(1535) on the free nucleon. Quasifree \(\eta \)-photoproduction on deuterium was explored for a comparison of the p(\(\gamma ,\eta \))p and n(\(\gamma ,\eta \))n cross sections. These data together with an upper limit for the d(\(\gamma ,\eta \))d reaction allowed a determination of the electromagnetic helicity amplitudes of the \(S_{11} \to N\) transition. Quasifree \(\eta \)-photoproduction on nuclei was used for a study of \(\eta \) nucleus final state interactions and the excitation of the \(S_{11}\)(1535) resonance in the nuclear medium. Finally a comparison of free and quasifree \(\pi ^0\)-production from the proton, the deuteron and from \(^{12}\)C shows a strong suppression of the resonance structure for nuclear targets.

abstract

We calculate the photoexcitation amplitudes for the \(\gamma + N \to {\mit \Delta }\)(1232) and \(\gamma + N \to N^*\)(1440) transitions in the chiral quark model including two-body exchange currents. We show that the contributions from the various two-body currents are important. Compared with present experimental data we see a slight worsening for the \(N\)–\({\mit \Delta }\) excitation but a small improvement for the transition to the Roper resonance (\(N^*\)(1440)) with respect to the impulse approximation.

abstract

Kaon photo- and electroproduction in all six isospin channels is investigated by means of an isobaric model. It is found that existing models can only partially describe the current experimental data. Moreover, the extracted coupling constants are mostly inconsistent with the prediction of SU(3) symmetry or the information from hadronic reactions. In order to further analyze this problem, we introduce a form factor at the hadronic vertices \(KNY\) (with \(Y = {\mit \Lambda }\) or \({\mit \Sigma }\)) and study its behavior qualitatively. Our result suggests the need of more accurate experiments, especially in the charged \({\mit \Sigma }\) and the neutral \(K^0\) channels.

abstract

We have studied the \(\gamma N \to \pi \pi N\) reaction using a model which includes N, \({\mit \Delta }\)(1232), \(N^*\)(1440) and \(N^*\)(1520) intermediate baryonic states and the \(\rho \)-meson as intermediate \(\pi \pi \) resonance. The model reproduces fairly well experimental cross sections below \(E_{\gamma } = 800\) MeV and invariant-mass distributions even at higher energies. One of the interesting findings of the study is that the \(\gamma N \to N^*\)(1520) \(\to {\mit \Delta }\pi \) process is very important and interferes strongly with the dominant \({\mit \Delta }\)-Kroll-Ruderman term to produce the experimental peak of the cross section.

abstract

As any composite, complex system the nucleon exhibits a rich excitation energy spectrum. The structure of these excitations — often called resonances because of their large decay widths — can be studied in \(\pi \)-induced and photonuclear reactions. In experiments at the electron accelerator MAMI mesonic decays of free resonances and of resonances bound in complex nuclei have been studied with the photon spectrometer TAPS. By comparing free to bound resonances, one is sensitive to possible modifications of baryon properties within the surrounding nuclear environment. An ensemble of mutually interacting baryon resonances can be generated in the central zone of relativistic heavy ion collisions as demonstrated in systematic studies of meson production at the heavy ion synchrotron SIS, utilizing TAPS and other detector systems.

abstract

The effects of rescattering for pions and kaons in the nuclear medium were analysed. The strong influence of rescattering was found for both regarded mesons.

abstract

We discuss various aspects of pion physics in the nuclear medium. We first study \(s\)-wave pion-nucleus interaction in connection with chiral symmetry restoration and quark condensate in the nuclear medium. We then address the question of \(p\)-wave pion-nucleus interaction and collective pionic modes in nuclei and draw the consequences for in medium \(\pi \pi \) correlations especially in the scalar–isoscalar channel. We finally discuss the modification of the rho meson mass spectrum at finite density and/or temperature in connection with relativistic heavy ion collisions.

abstract

The role of the \({\mit \Delta }\) resonance in subthreshold pion production is discussed and illustrated with \(\pi ^0\) data measured in heavy-ion collisions at 95 MeV/u with the photon spectrometer TAPS at GANIL. Particular emphasis is put on the \({\mit \Delta }\) capture reaction and a cross section for this process is obtained.

abstract

We present data on the decay of the \({\mit \Delta }\) resonance excited in \(^1\)H, \(^2\)H, \(^4\)He, \(^{12}\)C and \(^{208}\)Pb by the (\(^3\)He, \(t\)) reaction at 2 GeV incident energy. The quasi-free decay of the \({\mit \Delta }\) resonance and the absorption process are investigated. We find indication for a coherent process where a pion is emitted and the target nucleus is left in its ground state. This process is now being studied with the dedicated set-up Spes4\(\pi \). The first data with this new detection system have just been taken.

abstract

We calculate the forms of \(\omega \) and \(\rho \) resonances produced in the reactions \(pA \to VX \to e^+e^-X\) and \(\bar pA \to VX \to e^+e^-X\) at rest. The mass distributions have two component structure which corresponds to the decay of resonance outside and inside nucleus. The latter component has the mass and width distorted by nuclear medium. We investigate also the role of the final state interaction of decay products in the reactions \(\bar pA \to \rho X \to \pi ^+ \pi ^-X\) and \(\bar p A \to \omega X \to \pi ^0 \gamma X\).

abstract

The thermodynamic potential of an interacting system of pions and nucleons is calculated including the \(P_{33}\) \(\pi N\) resonance \({\mit \Delta }\)(1232). The resonance width is taken into account in a consistent manner.

abstract

The Balmer-like mass formula and quantization conditions derived from the first principles have been applied to systematic analysis of the gross structure of all known hadronic resonances. These equations are very useful at least for prediction and estimation of the invariant masses of unknown resonances. The correspondence principle between old classical and new quantum theories plays an outstanding role in the interpretation of the results and allows us to go even into fine details. We have demonstrated that the dimensional analysis, the principles of similitude and automodelity and the methods of analogy can put some bridge between the various branches of physics.

abstract

A new analysis of the \(S\)-wave production amplitudes for the reaction \(\pi ^- p_{\uparrow } \to \pi ^+ \pi ^- n\) on transversely polarized target was performed. The results can be of importance for the spectroscopy of scalar mesons and glue-balls.

abstract

A dense and hot pion system with a dynamically fixed particle number and an arbitrary charge is investigated with respect to ultra-relativistic heavy-ion collisions. The Lagrangian for describing such a system is derived from Weinberg’s chiral Lagrangian for the pion–pion interaction. Pion polarization operators are calculated within the Hartree approximation. The pion spectrum in the isospin symmetrical gas is presented. The effective in-medium pion gap depends sensitively on the density and the temperature, and it is found to exceed both the free pion mass and the corresponding value for the pion gas in chemical equilibrium. The possibility of a Bose–Einstein condensation is also discussed.

abstract

We provide a schematic view to some general aspects of chiral symmetry in matter using mean-field arguments. We use a simplified version of the Nambu–Jona–Lasinio model to formulate the ideas behind the thermodynamics at work in a variety of models with spontaneously broken chiral symmetry but without confinement. This version of the model is mapped onto chiral random matrix models, with some emphasis on the bulk behavior of the corresponding Dirac spectrum. Phase changes in the simplified model show up in the form of a rearrangement in the Dirac spectrum, with edge singularities that follow from mean-field exponents. The results are shared by a variety of models, and seem to be in quantitative agreement with some QCD lattice simulations. We comment on the relevance of microscopic and macroscopic universality in random matrix models, and the possible motivation for these models from QCD.

abstract

The selectivity of the \(\eta \)-decay branching ratios of the negative parity baryon resonances is discussed from a quark model perspective. It is shown that the selectivity can be understood as a consequence of the selective clustering into quark–diquark configurations with different quantum numbers that is caused by the pseudoscalar octet chiral meson exchange interaction between the constituent quarks. This leads to the prediction that the resonances \(N\)(1535), \({\mit \Lambda }\)(1670), \({\mit \Sigma }\)(1750) with mixed flavour-spin symmetry [2l]\(_{\rm FS}\)[21]\(_{\rm F}\)[21]\(_{\rm S}\) in their lowest order wavefunctions should have large \(\eta \) branching ratios, whereas the \(N\)(1650) and the \({\mit \Lambda }\)(1800) should not.

abstract

A relativistically covariant quark model developed on the basis of the Bethe–Salpeter equation is presented. The results for spectra, electro-weak decays and form factors in this model are discussed.

abstract

The nucleon light-cone wave function is expanded in terms of two-body meson-(bare baryon) Fock components. We find many interesting and surprising results for the flavour, spin and electromagnetic structure of the nucleon. The model leads to asymmetry of the light sea quarks which has important consequences for elementary Drell–Yan processes. We propose a further possibility to test this concept at HERA through the analysis of the structure of deep inelastic scattering (DIS) events induced by pion-exchange. Momentum and energy distributions of outgoing nucleons as well as rapidity and multiplicity distributions are investigated using Monte Carlo simulations. We investigate also possible consequences of the meson cloud in the nucleon for the production of \(W\) and \(Z\) bosons in the hadron–hadron collisions. A consistent analysis of deep-inelastic data and the gauge boson production data shows that the concept of virtual mesons in the nucleon is very useful in understanding the charged lepton asymmetry measured by the CDF collaboration at Fermilab. We critically study a possibility to test the \(\bar d\)–\(\bar u\) asymmetry in the nucleon by the analysis of some asymmetries possible to measure in principle at RHIC.

abstract

The absorption of pions of energy about 100 to 300 MeV is discussed. The results presented here are the results of a collaboration between Basel, Karlsruhe, LAMPF, Maryland, MIT, NMSV Las Cruces, ODU, PSI and Zagreb.

abstract

Data for \(\pi \)N and \(\overline K\)N scattering, reactions, and bound-states are examined with the chiral color dielectric model, the cloudy bag model, and a potential model. The behaviors of the \(T\) matrices in the complex energy plane as predicted by these models are used to interpret the data.

abstract

In this talk we present the results of recent developments in the application of Chiral perturbation theory to the \(K \bar K\) system and to the \(K^+ N \to KN\pi \) reaction close to threshold. In the first case we study the decay channels of the \(a_0\) and \(f_0\) mesons assumed to be made largely from \(K \bar K\). In the second case comparison is made with the present data. A qualitative agreement with experiment is found in both cases.

abstract

We investigate the dynamics of bound \(\bar qq\) systems in a covariant quasi-potential framework. In the spirit of the heavy baryon effective theory we restrict heavy quarks as spectators on their mass shell and evaluate multigluon exchange contributions up to \(\alpha ^3_S\). We suggest a systematic extension of the spectator picture to massless particles (light quarks and gluons) and discuss the connection between the instant and the front form in the limit of heavy quarks.

abstract

Two main fundamental issues in contrasting the lightcone field quantization to the canonical equal time quantization are the change of the boost problem to the rotation problem and realization of nontrivial vacuum phenomena on the lightcone. Motivated by the outcome of these issues, a lightcone quark model is constructed and various meson structure properties are calculated. The model predictions are compared with the experimental data including the meson radiative decay widths.

abstract

Pion absorption in the \(\pi ^+\) \(^3\)He \(\to ppp\) reaction is investigated using the Faddeev formalism. As preliminary results, the differential cross sections for the two- and three-body absorption mechanics are shown.

abstract

Hadron production in nucleon–nucleon, nucleon–nucleus and nucleus–nucleus interactions is considered in the framework of the Rossendorf collision model, which aims at describing simultaneously all reaction channels in a wide energy region. An empirical matrix element based on the partonic picture of hadrons is combined with the concept of intermediate subsystems and the calculation of modified statistical weights of the various final states. In case of nuclear reactions the Glauber concept is used to calculate the partial cross sections for the interaction of various numbers of participants. It is demonstrated that a large variety of experimental data can be satisfactorily reproduced. Predictions for proposed missing-mass measurements are discussed.

abstract

Our Galaxy is the largest nuclear interaction experiment which we know, because of the interaction between cosmic ray particles and the interstellar material. Cosmic rays are particles, which have been accelerated in the Galaxy or in extragalactic space. Cosmic rays come as protons, electrons, heavier nuclei, and their antiparticles. Up to energies up to some tens of TeV of particle energy it is possible to derive chemical abundances of cosmic rays. It has been proposed that cosmic ray particles can be attributed to three main sites of origin and acceleration, a) supernova shocks in the interstellar medium, b) supernova shocks in a stellar wind of the predecessor star, and c) powerful radio galaxies. This proposal leads to quantitative tests, which are encouraging sofar. Quantitative models for transport and interaction appear to be consistent with the data. Li, Be, B are secondary in cosmic rays, as are many of the odd-\(Z\) elements, as well as the sub-Fe elements. At very low energies, cosmic ray particles are subject to ionization losses, which produce a steep low energy cutoff; all particles belown the cutoff are moved into the thermal material population, and the particles above it remain as cosmic rays. This then changes the chemical abundances in the interstellar medium, and is a dominant process for many isotopes of Li, Be, B. With a quantitative theory for the origin of cosmic rays proposed, it appears worthwhile to search for yet better spallation cross sections, especially near threshold. With such an improved set of cross sections, the theory of the interstellar medium and its chemical abundances, both in thermal and in energetic particles, could be taken a large step forward.