We present a comparison in strength for the magnetic dipole transitions to the $0^{+}$ bandhead from the two possible extended proton-neutron interacting boson model $1^{+}$ states with either a mixed particle-hole character or a mixed proton-neutron character.

The $E2\mathrm{}$ transition $\gamma$-ray energies, the dynamical moments of inertia of the six superdeformed (SD) bands, and the energy differences $\Delta E_{\gamma }-\Delta E_{\gamma }^{\mathrm{ref}}$ of the SD band 6 of ${}^{148}\mathrm{Gd}$ have been investigated with a four- parameter formula in the spirit of perturbated SU(3) limit of the $\mathrm{sdg}$ interacting boson model. The calculated results agree with experimental data well. It indicates that the four-parameter formula approach is powerful in describing both the yrast SD band and the excited SD bands simultaneously, if the bands are not built upon those with a quasiparticle band crossing. In particular, the $\Delta I=4\mathrm{}$ bifurcation in the $\Delta I=2\mathrm{}$ superdeformed rotational band can be described well in the approach in which the perturbation holds ${\mathrm{SO}}_{\mathrm{sdg}}\mathrm{}\left(5\right)\mathrm{}$ symmetry.

Available experimental data for the $\Delta I=2\mathrm{}$ transition energies in superdeformed bands are analyzed by using an extended one-point formula. The existence of deviations from the smooth behavior is confirmed in many bands. However, we stress that one cannot necessarily speak about regular staggering patterns as they are mostly irregular. We present a simulation of the experimental data in terms of a simple model, which suggests that the irregularities may stem from the presence of irregular kinks in the rotational spectrum. However, at present, where such kinks may come from is an open question.

We have measured production yields and longitudinal momentum distributions of projectilelike fragments in the reaction ${}^{129}$Xe+${}^{27}$Al at an energy of $E_{\mathrm{lab}}$=790$A$ MeV. Production cross sections higher than expected from systematics were observed for nuclei in the neutron-deficient tails of the isotopic distributions. A comparison with previously measured data from the fragmentation of ${}^{136}$Xe ions shows that the production yields strongly depend on the neutron excess of the projectile with respect to the line of $\beta$ stability. The momentum distributions exhibit a dependence on the fragment neutron-to-proton ratio in isobaric chains, which was not expected from systematics so far. This can be interpreted by a higher excitation of the projectile during the formation of neutron-deficient fragments.

For 50 MeV/nucleon ${}^{129}\mathrm{Xe}{+}^{\mathrm{nat}}\mathrm{Sn}$ multifragmentation events, we deduced, by means of correlation techniques, the multiplicities of the hydrogen and helium isotopes which were emitted by the hot primary excited fragments produced at the stage of the disassembly of an equilibrated hot source. We also derived the relative kinetic energy distributions between the primary clusters and the light charged particles that they evaporate. From the comparison between the secondary multiplicities observed experimentally and the multiplicities predicted by the GEMINI model, we concluded that the source breaks into primary fragments which are characterized by the same $N/Z$ ratio as the combined system. Knowing the secondary light charged particle multiplicities and kinetic energies, we reconstructed the average charges of the hot fragments and we estimated their mean excitation energies. The fragment excitation energies are equal to 3.0 MeV/nucleon for the full range of intermediate mass fragment atomic number. This global constancy indicates that, on the average, thermodynamical equilibrium was achieved at the disassembly stage of the source.

Two-fragment reduced-velocity correlation functions were measured for small-impact-parameter collisions of ${}^{86}{\mathrm{Kr}\mathrm{}+}^{93}\mathrm{Nb}$ at $E/A=50\mathrm{}\hspace{0.5em}\mathrm{MeV}$ and compared to results of many-body Coulomb-trajectory calculations performed for instantaneous and sequential multifragment breakup scenarios. The correlation functions indicate emission on a very short time scale and appear consistent with an instantaneous breakup scenario, even though they exhibit a pronounced dependence on fragment kinetic energy when fragments are emitted at large transverse momenta. For the case of instantaneous breakup, sensitivities to initial-state momentum correlations due to total momentum conservation and to different emission patterns are investigated. For fragments emitted with large transverse momenta, momentum conservation constraints can cause a dependence of reduced-velocity correlation functions on fragment energy and fragment charge similar to those observed experimentally.

Light charged particles ($p,$$d,$$t,$${}^3\mathrm{He},$${}^4\mathrm{He}$) emitted in the reaction ${}^{40}{\mathrm{A}\mathrm{r}+}^{27}\mathrm{Al}$ at $60A\mathrm{MeV}$ have been studied in a large angular range, $15°<\theta <112.5\mathrm{}°.$ The data have been analyzed by supposing light charged particle emission from three equilibrated sources. Although the “temperatures” of the three sources as extracted from the slopes of the energy spectra are in agreement with other existing data, they are much higher than those extracted from the isotopic ratios. The anomalous abundance of α particles is also stressed and discussed.

An energy-dependent multipole analysis of the photodisintegration of deuterium has been performed for photon energies between 187 and 314 MeV using recent data taken with linearly polarized photons. A good fit is obtained with 11 free parameters determining eight multipoles. A wide variety of multipole solutions has been examined and in all cases the cross section with photon polarization parallel to the reaction plane is dominated by electric transitions, with $E2\mathrm{}\mathbf{\cdot }E1\mathrm{}$ interference responsible for the observed forward-backward angular asymmetry. The cross sections observed in perpendicular kinematics are dominated by magnetic multipoles. Several recent $N\Delta /NN$ coupled-channel calculations have predicted a pronounced 90° dip in the cross section that is absent from the data. This dip can be reproduced by changing the $M2\mathrm{}$ strength distribution in our fit. A comparison is made with multipoles calculated by Wilhelm and Arenhövel at 300 MeV.

The correct use of energy-dependent single-particle level (s.p.l.) densities within particle-hole state densities based on the equidistant spacing model (ESM) is analyzed. First, an analytical expression is obtained following the convolution of energy-dependent excited-particle and hole densities. Next, a comparison is made with results of the ESM formula using average s.p.l. densities for the excited particles and holes, respectively. The Fermi-gas model (FGM) s.p.l. densities calculated at the corresponding average excitation energies are used in both cases. The analysis concerns also the density of particle-hole bound states. The pairing correlations are taken into account while the comparison of various effects includes the exact correction for the Pauli exclusion principle. Quantum-mechanical s.p.l. densities and the continuum effect can also match a corresponding FGM formula, suitable for use within the average energy-dependent partial state density in multistep reaction models.

Comparing with intermediate-energy data for $(\overrightarrow{p},p^{\prime })$ spin-flip transitions, such as the one to the $6^{-},$ $T=1\mathrm{}$ state in ${}^{28}\mathrm{Si},$ we examine distorted-wave impulse-approximation predictions based on effective interactions derived from modern, high-precision nucleon-nucleon potentials. This establishes a reliable point of reference from which we explore medium effects in the context of a microscopic nucleon-nucleon $G$ matrix and estimate the reliability with which the scale and character of any novel medium effects could be determined.

An energy-dependent analysis of elastic scattering of ${\pi }^{+}$ from ${}^{12}\mathrm{C},$ ${}^{16}\mathrm{O},$ and ${}^{40}\mathrm{Ca}$ is made based on differential cross sections and (in one case) reaction cross sections. A nonlocal optical model is used to provide the energy variation between data sets. Structure is found in the $s$- and $p$-wave phase shifts.

We study the role of momentum cuts in fragment formation. The time evolution of nucleons is followed using the quantum molecular dynamics model. The fragments are formed within a minimum spanning tree description which allows two nucleons to be in the same fragment if their centriods are less than 4 fm. We introduce an additional condition by imposing a restriction in momentum space. Our analysis indicates that the effect of the cut (in momentum space) on fragment formation is stronger if the cut in the relative momentum of two nucleons is $<~150\mathrm{MeV}/c.\mathrm{}$ For higher values of the cut in the relative momentum of two nucleons $(>~200\mathrm{MeV}/c),$ fragment production with and without the momentum cut is the same. A cut of the order of the Fermi momentum (in the relative momentum of two nucleons) has a strong influence on the fragment distribution in central collisions whereas its effect is least in peripheral collisions. The fragment multiplicities and rapidity distributions obtained for central collisions with a cut of the order of the Fermi momentum $(=150\mathrm{}\mathrm{MeV}/c)$ matches at asymptotic times (after $120\mathrm{fm}/c$) with the most bound fragment structure obtained using a recently advanced simulated annealing clusterization algorithm.

A relativistic model for the inclusive photoproduction of η mesons on complex nuclei is introduced. The elementary production process is described using an effective Lagrangian approach. Contributions from several nucleon resonances in the second resonance region, as well as the Born and vector meson terms, are taken into account. The dynamics of nucleon motion are based on the relativistic mean field theory of Walecka. The η mesons are described by solutions of the Klein-Gordon equation. It is assumed that the inclusive process results from quasifree photoproduction on individual nucleons; the inclusive cross sections are obtained by integrating a set of exclusive quasifree cross sections. Distortion effects due to final state interactions of the outgoing η are taken into account. The calculated cross sections are compared with the available experimental data on ${}^{12}\mathrm{C}$ and ${}^{40}\mathrm{Ca},$ for photon energies from near threshold to about 800 MeV. The plane wave calculations are found to lie consistently above the data. Distortion effects lead to a strong suppression of the cross sections. Agreement with experiment is lacking when a set of parameters obtained from older data for the elementary process is used. The level of agreement is much improved when parameters based on recent elementary cross section data are used.

We study the possibility to influence the lifetime of nuclear isomeric states with the aid of incident fluxes of photons. We assume that a nucleus initially in an isomeric state $|i〉$ first absorbs an incident photon of energy $E_{\mathrm{ni}}$ to reach a higher intermediate state $|n〉$ and then the state $|n〉$ decays to a lower state $|l〉.$ In favorable cases the two-step induced emission rates become equal to the natural isomeric decay rates for incident power densities of the order of ${10}^{10}$ W cm${}^{-2}.$

A general theory of controlling and changing the spontaneous nuclear γ decay is proposed. The phenomenon of nuclear decay controlling is a result of the interaction of the excited nucleus with zero-energy electromagnetic modes, which in turn interact with the controlling screen. In the general case the spontaneous decay probability with the presence of adjacent material bodies always differs from the corresponding probability for free space. It is shown for the first time that the decay parameters greatly depend on the sign and magnitude of the radiation shift (radiation correction) of the resonance level position (nuclear analog of the Lamb shift for atom electrons). This shift is determined by processes of nucleus interaction with all zero-energy electromagnetic field modes (the lowest by energy or ground). It was shown that the resonant screen effect in all cases appears to be more significant than for the nonresonant one. The most influence on the nucleus spontaneous decay process will be realized in the case when the modes of the electromagnetic field in the zero-energy state, which interact with the nucleus, occur to be mutually synchronized. For this case the radiative lifetime may be increased by many orders of magnitude.

New experimental data on the behavior of the single-particle two-dimensional correlation functions $R$ versus $Q$ $(Q$ is the number of nucleons emitted from nuclei) and $A_p$ ${(A}_p$ is the mass of projectile nuclei) are presented. The interactions of protons, $d$, ${}^4\mathrm{He}$, and ${}^{12}\mathrm{C}$ nuclei with carbon nuclei (at a momentum of 4.2 A GeV/$c)$ are considered. The values of $R$ are obtained separately for ${\pi }^{-}$ mesons and protons. In so doing, the values of $R$ are normalized so that $-1<~R<~1$. The value of $R=0\mathrm{}$ corresponds to the case of the absence of correlations. It has been found that the $Q$ and $A_p$ dependence of $R$ takes place only for weak correlations $\mathrm{}(R<\mathrm{}0.3\mathrm{})\mathrm{}$. In the main (90%), these correlations are connected with the variable $p_t$ and have a nonlinear character; that is, the regions with different characters of the $Q$ dependence of $R$ are separated: there is a change of regimes in the $Q$ dependences of $R$. The correlations weaken with increasing $A_p,$ and the variable $R$ gets the lowest values of all the ones considered in ${}^{12}\mathrm{CC}$ interactions. Simultaneously with weakening the correlations in the region of large $Q$, the character of the $Q$ dependence of $R$ changes.

We study the production and the evolution of quark-gluon plasma expected to be formed in ultrarelativistic heavy-ion collisions, within the color flux-tube model. We introduce the gluonic component in the Boltzmann equation, which we solve in the phase space which is extended to include the SU(3) color degree of freedom. The color degree of freedom is shown to play a decisive role in equilibration, and in fixing the temperature of the plasma. We further find that the soft partons that we study here contribute substantially to the bulk properties. Finally, the model is shown to provide a detailed picture of how the quark-gluon plasma evolves and is driven towards a hydrodynamic flow, which starts occurring around 1 fm.

We study photon production from the hidden local symmetry approach that includes π, ρ, and $a_1$ mesons and compute the corresponding photon emission rates from a hadronic gas in thermal equilibrium. Together with experimental radiative decay widths of the background, these rates are used in a relativistic transport model to calculate single photon spectra in heavy-ion collisions at SPS energies. We then employ this effective theory to test three scenarios for the chiral phase transition in high-temperature nuclear matter including decreasing vector meson masses. Although all calculations respect the upper bound set by the WA80 Collaboration, we find the scenarios could be distinguished with more detailed data.

We calculate the photon production cross section arising from the hard scattering of partons in nucleon-nucleon collisions by taking into account the intrinsic parton transverse momentum distribution and the next-to-leading-order contributions. As first pointed out by Owens, the inclusion of the intrinsic transverse momentum distribution of partons leads to an enhancement of photon production cross section in the region of photon transverse momenta of a few $\mathrm{GeV}/c$ for nucleon-nucleon collisions at a center-of-mass energy of a few tens of GeV. The enhancement increases as $\sqrt{s}$ decreases. Such an enhancement is an important consideration in the region of photon momenta under investigation in high-energy heavy-ion collisions.

We study the dynamics of quantum fluctuations which take place at the earliest stage of high-energy processes and the conditions under which the data from $e$-$p$ deep-inelastic scattering may serve as an input for computing the initial data for heavy-ion collisions at high energies. Our method is essentially based on the space-time picture of these seemingly different phenomena. We prove that the ultraviolet renormalization of the virtual loops does not bring any scale into the problem. The scale appears only in connection with the collinear cutoff in the evolution equations and is defined by the physical properties of the final state. In heavy-ion collisions the basic screening effect is due to the mass of the collective modes (plasmons) in the dense nonequilibrium quark-gluon system, which is estimated. We avoid the standard parton phenomenology and suggest a dedicated class of evolution equations which describe the dynamics of quantum fluctuations in heavy-ion collisions.