Table of contents

We extend the method of time delay proposed by Eisenbud and Wigner, to search for unstable states formed by η mesons and the ³He nucleus. Using few-body equations to describe η³He elastic scattering, we predict resonances and unstable bound states within different models of the η–N interaction. The η³He states predicted within this novel approach are in agreement with the recent claim of the evidence of η-mesic ³He made by the TAPS Collaboration.

At high temperatures, strongly interacting matter becomes a plasma of deconfined quarks and gluons. In statistical quantum chromodynamics, deconfinement and the properties of the resulting quark–gluon plasma can be investigated by studying the in-medium behaviour of heavy quark bound states. In high energy nuclear interactions, quarkonia probe different aspects of the medium formed in the collision. We survey the results of recent charmonium production studies in SPS and RHIC experiments.

The BRAHMS and PHOBOS collaborations recently revisited the limiting fragmentation shown in the charged particle pseudorapidity density distribution in Au + Au collisions at RHIC energies. The PHOBOS collaboration especially emphasized that the observations of the charged particle universal (pseudo)rapidity scaling (limiting fragmentation) in and Au + Au collisions at relativistic energies may play an important role in the study of reaction dynamics. We use a parton and hadron cascade model, PACIAE, to investigate the charged particle universal (pseudo)rapidity scaling in the above collisions. It is pointed out that, because the universal scaling was observed in the tail region of the (pseudo)rapidity distributions, the discrepancies among distributions may not be properly visible. Therefore, this universal scaling may not have much to do with reaction dynamics, especially quark–gluon plasma. In addition, the charged particle universal scaling observed in the hadronic final state seems to arise from the partonic initial state.

We perform a microscopic evaluation of nuclear generalized parton distributions (GPDs) for spin-0 nuclei in the framework of the Walecka model. We demonstrate that the meson (non-nucleon) degrees of freedom dramatically influence nuclear GPDs, which is revealed in the non-trivial and unexpected A-dependence of deeply virtual Compton scattering (DVCS) observables. In particular, we find that the first moment of the nuclear D-term d_A(0) ∝ A^2.26, which confirms the earlier prediction of Polyakov. We find that in the HERMES kinematics, contrary to the free proton case, the nuclear meson degrees of freedom in large nuclei enhance the nuclear DVCS amplitude which becomes comparable to the Bethe–Heitler amplitude and, thus, give the non-trivial A-dependence to the DVCS asymmetries: as a function of the atomic number, the beam–charge asymmetry increases whereas the beam–spin asymmetry decreases slowly.

A systematic description of the yrast superdeformed (SD) bands in N = 114, Z = 80–84 isotone nuclei using the projected shell model is presented. The calculated γ-ray energies, moment of inertia and M1 transitions are compared with the data for which spin is assigned. Excellent agreement with the available data for all isotones is obtained. The calculated electromagnetic properties provide a microscopic understanding of those measured nuclei. Some predictions in superdeformed nuclei are also discussed.

Excited states of ¹²³I were populated via the ¹¹⁶Cd(¹⁴N, α3n) reaction at 65 MeV. The resultant γ-rays were detected using standard γ-ray spectroscopic techniques with the NORDBALL detector array. Two previously known positive-parity ΔI = 2 sequences have been extended up to 31/2⁺ and 41/2⁺. In addition, a number of ΔI = 1 transitions linking the two ΔI = 2 sequences have been observed. It is suggested that both ΔI = 2 sequences are based on a common configuration. This ΔI = 1 band is proposed to be built predominantly on the g_7/2[404]7/2⁺ oblate configuration, based on the energy-level spectra, B(M1)/B(E2) ratios and the theoretical predictions from the particle-rotor model. The previously identified ΔI = 1 rotational band built on the prolate g_9/2[404]9/2⁺ orbital has also been extended to higher spins. Another previously identified but weakly populated ΔI = 1 band is confirmed and is proposed to be built on the d_5/2[413]5/2⁺ configuration with the ground state of ¹²³I as the bandhead.

Ultraperipheral heavy ion collisions (UPCs) are an important alternative for studying QCD dynamics until the next generation of e⁺e⁻/ep/eA colliders becomes a reality. Due to the coherent action of all the protons in the nucleus, the electromagnetic field is very strong and the resulting flux of equivalent photons is large, which allows us to study two-photon as well as photonuclear interactions at high energies. In this paper we present a brief review of the vector meson production in UPCs at high energies using the QCD colour dipole approach to describe their photonuclear production and the perturbative QCD Pomeron (BFKL dynamics) to describe the double meson production in photon–photon processes. Predictions for rates and integrated cross sections are presented for energies of RHIC and LHC.

In the framework of the Glauber model, taking into account the K'-factor, we analyse the Drell–Yan dimuon production cross sections for an absolute measurement of continuum dimuon (Drell–Yan) cross section in 800 GeV/c pp collisions. The calculated results of the leading order agree only poorly with the new experimental data, but there is a general agreement between the next-to-leading-order QCD correction results and the experimental data. It is shown that the QCD corrections to the Drell–Yan process cannot be omitted. Then, by means of the nuclear parton distribution obtained from the DGLAP equation, taking into account the energy loss of the beam proton through the nucleus, we analyse the QCD corrections to the measured Drell–Yan production cross sections for an 800 GeV proton beam incident on Be, Fe and W nuclear targets in the Glauber model. It is shown that the theoretical results are in good agreement with the FNAL E866. Finally, we compare the calculated results from the DGLAP equation with those from the latest nuclear effect models.

We investigate the use of hybrid schemes for the calculation of low-energy eigenstates of shell model Hamiltonians. These schemes mix the basic ideas behind the quantum Monte Carlo diagonalization (QMCD) method and the VAMPIR method. In applications to some fp nuclei using the GXPF1 effective Hamiltonian, we find most practical and time saving the use gradient methods (typical of the VAMPIR approach) with QMCD trial wavefunctions, which are Slater determinants for fp nuclei. We find that the number of many-body states needed to reach reasonable values of the ground-state energies for a given angular momentum is small. We also explore the possibility of using these hybrid methods for model Hamiltonians with a strong repulsive core.

The goal of the present analysis is to find, in the free neutron beta decay, the expressions for the decay rate and the electron asymmetry that contain all the theoretical effects at the 10⁻⁴ level. This accuracy is better than the current experimental precision that modern experiments allow. For this aim it is necessary to study the strong interaction effects, the radiative corrections and the recoil of the proton. A conceptual problem that we discuss in detail is the Fermi function additivity. The model dependence in the radiative corrections yields important effects which must be incorporated. We show that this is the only source of uncertainty that is out of control still at the mentioned order. As an application, we compare the values of the CKM matrix element |V_ud | from this decay with the values both from the superallowed Fermi transition beta decays and the unitarity of the CKM matrix. We discuss the relevance of the observed discrepancies.

The dynamical cluster-decay model (DCM) is extended to a positive Q-value (Q_out), heavy compound system ¹¹⁶Ba*, with complete angular momentum and charge dispersion effects included in it. The contributions due to both the light particles (LPs) and intermediate mass fragments (IMFs) are considered to give the total cross section. Interestingly, instead of the complete IMF spectrum observed for lighter systems such as ⁴⁸Cr* and ⁵⁶Ni*, here two small 'windows of IMFs' are predicted, one for light masses (2 ⩽ Z ⩽ 9) and another for the heavy mass end of symmetric and nearly symmetric fragments (14 ⩽ Z ⩽ 28), in agreement with the available data for the light mass 'IMF window' and its indications of possible extension to the heavier mass fragments. Within a non-statistical model description, the definition of phase space is found to be contained in the DCM definition of the 'IMF window' for the compound nucleus process. As in experiments, the calculated excitation functions are shown to put a limit on the minimum incident centre-of-mass energy required for the production of IMFs, and it will be of further interest to observe in experiments the predicted structures in the excitation functions of both the individual fragments, like for ¹²C decay, and the summed-up cross sections. Also, further measurements of the total kinetic energies of the fragments are called for.

A simultaneous description of non-strange nuclei and hypernuclei is provided by a single mass formula inspired by the spin–flavour SU(6) symmetry breaking. This formula is used to estimate the hyperon binding energies of lambda, double lambda, sigma, cascade and theta hypernuclei. The results are found to be in good agreement with the available experimental data on 'bound' nuclei and relativistic as well as quark mean-field calculations. This mass formula is useful to estimate binding energies over a wide range of masses including the light mass nuclei. It is not applicable to a repulsive potential.

A new set of Nilsson parameters, with the isospin-dependent spin–orbit potential (κ) and l²_t term (μ), is proposed for neutron-rich nuclei of Ne and Mg isotopes. The ground-state deformations and B(E2) values of Ne and Mg nuclei around N = 20 are studied within the framework of the macroscopic–microscopic (MM) model with the new set of Nilsson parameters. The calculated results are compared with the experimental data. The experimental large deformations and B(E2) values are well reproduced by the new calculation of this paper. The calculated results are also compared with the recent results of mean-field models and shell models. Detailed discussions of the shell structure around N = 20 are given. It is predicted that the enhanced negative shell correction energies at deformed shape and the weak N = 20 magic shell closure lead to the large deformations for Ne and Mg nuclei around N = 20.

We discuss the possibility of determining the parity of the Θ⁺ baryon from the photoproduction process γN → KΘ⁺ near threshold. We utilize the conservation laws of parity and angular momentum for the analysis of angular distributions and spin observables near threshold. Since the discussion is in essence a partial wave analysis of the production mechanism, the result should be less dependent on the model parameters. Our analysis shows that the angular distribution and photon polarization asymmetry for the process of a neutron target are sensitive to the parity of the Θ⁺, but not for the case of a proton target. In the case of proton target, the polarization asymmetries of target and recoiled Θ⁺ are preferred for parity determination.