Table of contents

The authors study the mass of the ssuu system within a sum rule approach in order to see if the S(975) and delta (980) are exotic mesons.

The possibility of the existence of liberated quarks in zero-temperature nuclear matter is briefly considered. It is argued that at densities close to the normal one the quark admixture is allowed. However, constituent quarks can carry only a small fraction of the baryon number of the system.

The quantity S(E1) defined by Hausser (1973) is calculated for ^6,7Li using a harmonic oscillator description of these nuclei. The centre-of-mass problem is treated exactly and all the dipole strength is considered. It is found that S(E1) depends mainly on the residual interaction splitting the giant dipole resonance. Previous treatments based on single-particle and cluster descriptions are discussed.

The authors show that the EMC effect can be explained without the assumption of any significant changes of the nucleon quark structures in the medium. They discuss some other approaches to the nuclear deep inelastic scattering.

The dynamic deformation model (DDM) of Kumar, (1984), has been applied to the nucleus ¹²⁴Te and the results support its description as gamma -unstable. The labelling of states and the E2 selection rules for a gamma -unstable nucleus are discussed. Experimental data for energies and E2 transitions are compared both with the DDM results and with those from a fitted calculation in the interacting boson model (IBM-1).

A model for the fragmentation of heavy quarks is proposed, based on a scheme used previously to calculate hadron structure functions. It embodies the hardness expected from the decay kinematics, and is consistent with 'reciprocity', which demands that the fragmentation function should be related to the hadronic structure function. It agrees with the data on c and b quark fragmentation, but its predictions for t and other very heavy quarks are significantly different from the model of Peterson et al., (1983), for example.

Effects of the Pauli principle in the calculation of the pi d scattering length are considered. In the S wave, the main effect is due to a blocking of the charge-exchange channel and modified the pi N amplitude in the presence of further nucleons. For a numerical illustration the author has performed some model calculations in a second-order multiple-scattering expansion.

In a recent measurement of Pd( pi , pi ') on four even isotopes, values of proton and neutron matrix elements, M_p and M_n, were extracted from the data. For the lowest 2⁺ state the author shows that the measured values contain two independent pieces of information: e_n/e_p, the ratio of neutron to proton effective charge, and e_pA_sp, the proton effective charge times a single-particle matrix element. Both quantities can be obtained from the data without recourse to the IBA.

The authors apply the bremsstrahlung model for pion production to symmetric nuclear collisions at energies far below the single NN threshold. There they expect this mechanism to be dominant. Once the deceleration parameter of the theory is adjusted, all main features of recent neutral-pion measurements can be explained. The parameter is close to hydrodynamical values. Since the gamma -ray bremsstrahlung also reflects the kinematics of its source, a simultaneous measurement of pion and gamma -ray bremsstrahlung can be used to further test the collision dynamics. The results of the calculations for both kinds of radiation are presented. In addition they show that for higher bombarding energies the thermally produced pions can fill the gap between the bremsstrahlung and the experimental data.

A simple microscopic model has been presented to calculate the energy dependence of the real and imaginary parts of the heavy-ion interaction potential. The results obtained from a simple effective interaction and Skyrme interaction in this formalism show that the imaginary part of the potential becomes more and more attractive with increasing relative centre-of-mass energy E_CM unlike the real part of the potential which exhibits a 'switching over' phenomenon. The elastic scattering cross sections for ¹⁶O+⁴⁰Ca (E_CM=28.57 MeV) and ⁴⁰Ca+⁴⁰Ca (E_CM=71.8, 88, 93, 112.5 and 120 MeV) calculated from such potentials are in good agreement with the phenomenological results. Values of the Fresnel interaction radius, the grazing angular momentum and the total cross section obtained in the sharp cut-off model from the elastic scattering angular distributions of ⁴⁰Ca+⁴⁰Ca are consistent with their corresponding values computed from the optical model calculation. The position and height of the fusion barrier and fusion cross sections of ⁴⁰Ca+⁴⁰Ca at different values of E_CM calculated in the Hill-Wheeler parabolic approximation also compare well with the experimental results.

Neutron elastic scattering analysing powers have been measured at 3 MeV incident energy for ^natW, ^natHg, ^natTl, ^natPb, ²⁰⁹Bi and ²³⁸U. Differential cross sections have also been measured for ^natHg, ^natTl, ^natPb and ²⁰⁸Bi. A local, phenomenological, spherical optical model analysis of these data is performed with comparison made between pure Woods-Saxon real form factors and those having surface-peaked components. The latter have been predicted in dispersion integral calculations. The effects of introducing an imaginary spin-orbit potential component are also tested. For ^natW and ²³⁸U a deformed phenomenological optical potential is used in coupled-channels calculations. Coupled-channels effects are also investigated for ²⁰⁸Pb, assuming it to be a harmonic vibrator. Microscopic calculations of real and imaginary potentials are made using the methods of Brieva and Rook, (1977,8), and Jeukenne et al. (1977). Calculation of the spin-orbit interaction is less sophisticated with an energy- and density-independent form used. At 3 MeV compound elastic scattering must be accounted for in all nuclei presently studied. This has been calculated using a recent formulation of the statistical model.

A pair of optical filters, one with transmission characteristics compatible with the atmospheric fluorescent bands and the other responding to longer wavelengths lying outside these bands, is shown to provide an efficient method for detecting fluorescent events in the presence of background Cerenkov emissions. The attendant reduction in the light of the sky at night provides the additional advantage of a higher signal-to-noise ratio.

Monte-Carlo calculations on gamma families at mountain altitude (4500 m) have been carried out for appropriate scaling model parameters which are currently used in high-energy cosmic-ray phenomenology. There are no correlations between Feyman's variable x and the fractional energy f' taken by the gamma rays. The rejuvenated an non-rejuvenated families select secondaries with average x values 0.14 and 0.12, respectively. The so called pionisation region also contributes to family formation (40% secondaries at x<0.1). The model involving an increase in the interaction cross section due to scaling violation in the x<0.1 region is not in agreement with the experimental multiplicity distribution.

Analysis of the EAS electron and muon components obtained in the Tien-Shan experiment shows that the secondary particle multiplicity depends on the interaction energy in the range approximately 10¹⁵ eV essentially more strongly than is predicted from accelerator experiments. A primary mixed composition rich in protons is the most probable.

The configurations of multi-muon events have been investigated in detail by a three-dimensional Monte-Carlo simulation, including recent features of high-energy collisions observed in a p-p collider. The average properties and topology of individual multi-muon events at depths 1800, 4200 and 5000 mWe underground are studied. Some criteria are suggested to identify average primary mass composition. The important link between multi-muon events and high multiplicity fluctuations or more copious multi-particle production in the energy range 10⁶-10⁷ GeV has been pointed out.