Table of contents

The authors find that pseudovector pi N coupling gives a Perey effect suppression in the matrix element in (p,d) reactions. This is in contrast to the case of pseudoscalar coupling where there is no suppression.

The charge-exchange two-nucleon invariant mass spectrum for deuteron breakup at 3.3 GeV/c is investigated using a one-pion-exchange model. Kinematical cuts are introduced so as to reproduce those taken in a 1976 Dubna experiment. The authors find that these cuts have substantial effects on the position and width of the mass spectrum in the delta resonance region.

The differential cross section, vector analysing power and three components of the second-rank tensor analysing power were measured for quasi-elastic scattering of 170 MeV ²³Na from ²⁰⁸Pb. The data have been successfully interpreted in terms of the tidal symmetry model and the sign and magnitude of the observed polarisation effects are in good agreement with the known quadrupole moment of ²³Na.

The main features of purely phenomenological and quark-gluon string models are analysed with respect to the momentum distribution of the secondary particles in high-energy hadron interactions. Some predictions of both models are discussed.

The authors construct an extension of the gauge technique to two-dimensional supersymmetric gauge theories. This involves a derivation of the spectral representation of a scalar superpropagator in two dimensions. They apply the method to the massive supersymmetric Schwinger model. In the case that the gauge multiplet mass equals twice that of the matter multiplet they determine the spectral functions of the matter propagator.

Owing to a strong suppression of two-body mechanisms, the ³He( gamma ,2p)n reaction is dominated by three-body exchange currents, and appears to be the best place to study them. Relevant kinematics are proposed and discussed.

Displacements of the energy centroids of the distinct isospin fragments of the isovector giant resonances of nuclear multipole excitations are obtained within the framework of an isoinvariant RPA. The isovector contribution of the displacements is shown to be independent of the ground-state correlations (GSC) as well as of the multipolarity, whereas the isotensor contribution is found to have a simple dependence on multipolarity and a very vital dependence on the GSC. The latter comes out to be in quantitative agreement with an independent estimate by Lane and Mekjian (1981). It is also shown that, for the spurious (isoscalar dipole) excitation, the well known vanishing excitation energy would lead to vanishing strength as well. The two parameters measuring the above contributions have been estimated numerically, using a few well established model and empirical parameters, and the results agree quite well with the existing experimental findings. These also include confirmation of multipolarity independence of the isovector contribution and the essentially renormalising effect of the isotensor contribution.

Using the realistic single-particle energy spectrum obtained in the Woods-Saxon nucleon mean-field potential, the authors calculate the BCS pairing gap for ⁵⁸Ni as a function of temperature taking into account the thermal and particle-number fluctuations. The strength distributions of the electric dipole transitions and the centroids of the isovector giant dipole resonance (IV-GDR) are computed in the framework of the finite-temperature random-phase approximation (RPA) based on the Hamiltonian of the quasiparticle-phonon nuclear model with separable dipole forces. It is shown that the change of the pairing gap at finite temperature can noticeably influence the IV-GDR localisation in realistic nuclei. By taking both thermal and quasiparticle fluctuations in the pairing gap into account the effect of the phase transition from superfluid to normal in the temperature dependence of the IV-GDR centroid is completely smeared out.

The Hoodbohoy-Jaffe formalism of quark exchange in a nuclear system has been used to calculate the nucleon structure function for nuclear matter. The authors include only two-quark exchange and they use their LOCV correlation functions for nucleons. It is shown that in general the quark exchange contributes significantly to the EMC ratio and it improves their understanding of EMC data.

The authors show that a consistent dispersion-relation analysis of neutron scattering by ⁴⁰Ca removes the anomaly at low energies in the total cross section.

A complex two-body effective interaction derived from the Skyrme interaction is used in the folding model (FM) and energy density model (EDM) to obtain the energy-dependent real and imaginary parts of the heavy-ion (HI) optical potential. A comparison of these calculated potentials and their predicted values for the elastic scattering cross section of ⁴⁰Ca+⁴⁰Ca(E_CM=120 MeV) with the phenomenological data shows that the potentials are more accurately determined in the EDM. The effects of nuclear surface, Pauli-blocking, antisymmetrisation due to kinetic-energy density and exchange of the interaction matrix on the calculated FM and EDM potentials and their corresponding elastic scattering cross sections of ⁴⁰Ca+⁴⁰Ca are found to be significant. The role of real and imaginary potentials in ⁴⁰Ca+⁴⁰Ca scattering is also investigated.

Differential cross sections, excitation functions, and vector (and tensor) polarisations have been calculated for pion elastic and inelastic scattering off ⁶Li near the Delta ₃₃-resonance energy. A momentum-space coupled-channel formalism has been used. It contains the usual first-order term and a phenomenological rho ² term, the parameters of which were determined earlier from pi -¹²C experimental data. Cluster and phenomenological shell-model wavefunctions of the Li nuclear states are shown to produce quantitatively different results for the vector polarisation. At the same time the differential cross sections corresponding to the two nuclear models differ at moderate momentum transfers mainly in their absolute values.

The ( pi ⁺, pi ^-) reactions leading to the double isobaric analogue state (DIAS) have been studied at pion energies 50 to 300 MeV, with ¹⁴C as an example. The emphasis of the study has been on the effects of the pion-nucleon interaction range on the calculated double-charge-exchange (DCX) cross sections. The authors found that both the propagation of the intermediate pi ⁰ and the nucleon-nucleon correlation at short distances are strongly affected by the non-locality of the pi N interaction. Consequently, DCX reactions may be used to distinguish between different pi N interaction models.

A three-dimensional simulation of muon and electron components has been performed for showers with energies 2*10⁴ and 2*10⁷ GeV, using a model which takes into account the most important results in recent UA1 and UA5 CERN collider data. Lateral muon structure functions become steeper with increasing energy and the index alpha in Delta _mu approximately=N_e^alpha decreases with distance from values near 0.85 around 5 m down to 0.43 at approximately 2 km from the shower axis, at a fixed depth of 700 g cm^-2 (this variation is even more important at sea level). Since densities in small showers are recorded inside 50 m, an apparent exponent alpha which is observed to be around 0.75 can ultimately be in agreement with alpha =0.68 in N_mu approximately=_e^alpha (and similarly at sea level); consequently heavy compositions or different multiproduction need no longer be invoked to explain this aspect of cosmic-ray data, at least in the energy band 2*10⁴-2*10⁵ GeV.

Simple expressions for secondary-particle spectra are derived on the basis of the quark-gluon string model for hadron interactions. The parametrisation is prepared for application in extensive-air-shower calculations for verification of the model at high cosmic ray energies. An analysis of the model is made using available experimental data. It reveals violation of Feynman scaling in secondary-particle momentum distributions. An exclusive description of the interaction is made clarifying the range where this model can be applied.

A Monte Carlo generator for p-A collisions has been developed which employs some concepts include in the dual-parton model and which has been adapted to reproduce some results obtained by the European Hybrid Spectrometer at CERN at 360 GeV/c. The important effect of the violation of KNO scaling which increases with A and with primary energy, on the behaviour of cascades in dense media is illustrated by a Monte Carlo simulation of hadron-electron showers and subsequent comparison with CERN results at 300 GeV. These effects are expected to be even more important at cosmic-ray energies.