The interplay between spectator and participant matter in heavy-ion collisions is investigated in the context of a microscopic transport model. Transport simulations show that flow patterns for the participant matter are strongly influenced by the presence of the nearby spectator matter. However, the influence is mutual. During the explosion of the participant zone, the spectator matter acquires a transverse momentum $〈P^x/A〉$ that shows sensitivity to the nuclear incompressibility and to the momentum dependence of the nuclear mean field (MF). An observed change in the net average momentum per nucleon, $\Delta |〈\mathbf{P}/A〉|,$ can be associated with the momentum dependence of the MF. For a momentum-dependent MF and a low impact parameter in a heavy system, the spectators may emerge faster than in the initial state, accelerated by the violent participant explosion. The average excitation energy and the mass of the spectators, in contrast to the momentum, show little sensitivity to the nuclear equation of state.

Motivated by a schematic model of multiple parton scattering within the Glauber formalism, the transverse momentum spectra in $\mathrm{pA}$ and $\mathrm{AA}$ collisions are analyzed in terms of a nuclear modification factor with respect to $\mathrm{pp}$ collisions. The existing data at the CERN Super Proton Synchrotron energies are shown to be consistent with the picture of Glauber multiple scattering in which the interplay between soft and hard processes and the effect of absorptive processes lead to nontrivial nuclear modification of the particle spectra. Relative to the additive model of incoherent hard scattering, the spectra are enhanced at large $p_T$ (hard) by multiple scattering while suppressed at low $p_T$ (soft) by absorptive correction with the transition occurring at around a scale $p_0\sim 1-2\hspace{0.5em}\mathrm{GeV}/c$ that separates soft and hard processes. Around the same scale, the $p_T$ spectra in $\mathrm{pp}$ collisions also change from an exponential form at low $p_T$ to a power-law behavior at high $p_T.$ At very large $p_T\gg p_0,$ the nuclear enhancement is shown to decrease as ${1/p}_T^2.$ Implications of these nuclear effects on the study of jet quenching, parton thermalization, and collective radial flow in high-energy $\mathrm{AA}$ collisions are discussed.

Pion-nucleon elastic scattering in the dominant $P_{33}$ channel is examined in the model in which the interaction is of the form $\pi +N\leftrightarrow N,\hspace{0.5em}\Delta \mathrm{}\left(1232\right).$ New expressions are found for the elastic pion-nucleon scattering amplitude which differ from existing formula both in the kinematics and in the treatment of the renormalization of the nucleon mass and coupling constant. Fitting the model to the phase shifts in the $P_{33}$ channel does not uniquely fix the parameters of the model. The cutoff for the pion-nucleon form factor is found to lie in the range $\beta =750\mathrm{}\pm 350\hspace{0.5em}\mathrm{MeV}/c.\mathrm{}$ The masses of the nucleon and the $\Delta$ which would arise if there were no coupling to mesons are found to be $m_{{}_N}^{\mathrm{}\left(0\right)\mathrm{}}=1200\mathrm{}\pm 200\hspace{0.5em}\mathrm{MeV}$ and $m_{\Delta }^{\mathrm{}\left(0\right)\mathrm{}}=1500\mathrm{}\pm 200\hspace{0.5em}\mathrm{MeV}.$ The difference in these bare masses, a quantity which would be accounted for by a residual gluon interaction, is found to be $\delta m^{\mathrm{}\left(0\right)\mathrm{}}=350\mathrm{}\pm 100\hspace{0.5em}\mathrm{MeV}.$

The mass shift, width broadening, and spectral density for ρ and ω mesons in a heat bath of nucleons and pions are calculated using a general formula which relates the self-energy to the real and imaginary parts of the forward scattering amplitude. We use experimental data to saturate the scattering amplitude at low energies with resonances and include a background Pomeron term, while at high energies a Regge parametrization is used. The real part obtained directly is compared with the result of a dispersion integral over the imaginary part. The peaks of the spectral densities are little shifted from their vacuum positions, but the widths are considerably increased due to collisional broadening. Where possible we compare with the UrQMD model and find quite good agreement. At normal nuclear matter density and a temperature of 150 MeV the spectral density of the ρ meson has a width of 345 MeV, while that for the ω is in the range 90–150 MeV.

A microscopic calculation of Compton scattering on the nucleon is presented which encompasses the lowest energies—yielding nucleon polarizabilities—and extends to energies of the order of 600 MeV. We have used the covariant “dressed K-matrix model” obeying the symmetry properties which are appropriate in the different energy regimes. In particular, crossing symmetry, gauge invariance and unitarity are satisfied. The extent of violation of analyticity (causality) is used as an expansion parameter.

Incoherent photoproduction of the $\eta$ meson on the deuteron is studied for photon energies from threshold to 800 MeV. The dominant contribution, the $\gamma N-\eta N$ amplitude, is described within an isobar model. The final state interaction derived from the CD-Bonn potential is included and found to be important for the description of the production cross section close to threshold. Possible effects from the $\eta N$ final state interaction are discussed.

Levels in ${}^{112}\mathrm{Cd}$ have been studied through the ${(n,n}^{\prime }\gamma )$ reaction with monoenergetic neutrons. An extended set of experiments that included excitation functions, $\gamma$-ray angular distributions, and $\gamma \gamma$ coincidence measurements was performed. A total of 375 $\gamma$ rays were placed in a level scheme comprising 200 levels (of which 238 $\gamma$-ray assignments and 58 levels are newly established) up to 4 MeV in excitation. No evidence to support the existence of 47 levels as suggested in previous studies was found, and these have been removed from the level scheme. From the results, a comparison of the level density is made with the constant temperature and back-shifted Fermi gas models. The back-shifted Fermi gas model with the Gilbert-Cameron spin cutoff parameter provided the best overall fit. Without using the neutron resonance information and only fitting the cumulative number of low-lying levels, the level density parameters extracted are a sensitive function of the maximum energy used in the fit.

Contributions to the neutron’s electric dipole moment (EDM), $d_n,$ are calculated using a well-constrained ansatz for the nucleon’s Poincaré covariant Fadde’ev amplitude. The momentum-dependent quark dressing amplifies the contribution from the current-quarks’ EDMs; and dressed-quark confinement and binding make distinguishable the effect of the two $\mathrm{CP}$ and T violating interactions: $i{\gamma }_5{\sigma }_{\mu \nu }{(p}_1-p_2{)}_{\nu }$ and ${\gamma }_5{(p}_1{+p}_2{)}_{\mu },$ where $p_{1,2}$ are the current-quarks’ momenta. The value of $|d_n|$ obtained using the current-quark EDMs generated by a minimal three Higgs doublet model of spontaneous $\mathrm{CP}$ violation is close to the current experimental upper bound.

A simple functional form has been found that gives a good representation of the total reaction cross sections for the scattering from ${}^{12}\mathrm{C}$ and from ${}^{208}\mathrm{Pb}$ of protons with energies in the range 20–300 MeV.

In many isotopes important to nucleosynthesis theory there exists a low-lying metastable state whose deexcitation to the ground state is strongly inhibited by a large angular momentum difference. In a stellar plasma, the equilibration of the ground and metastable states of such nuclei proceeds primarily via indirect transitions that involve upper-lying levels. We present a mathematical technique to follow these multistep transitions. Under the crucial assumption that the abundances of the upper-lying levels are in a steady-state abundance distribution, our method abstracts away all the higher-lying excited states allowing the isotope in question to be represented as a two-state system with transitions between these two states. The two states are properly not the ground and metastable states themselves but rather two ensembles of states, one tied to the ground state and one tied to the metastable state. We show how to compute effective rates into and out of these ensembles and between them, as well as how to identify the dominant pathways. This allows such nuclei to be treated in a simple, straightforward, and accurate fashion in nucleosynthesis networks. The specific example of ${}^{26}\mathrm{Al},$ including its effective beta-decay lifetime, is considered in detail.

In the standard development of scattering theory the Hamiltonian of the system plays a central role; however when the Bakamjian-Thomas method is used to construct a relativistic model of a few-particle system, the mass operator plays the essential role. Here a simple procedure for translating the Hamiltonian formulation of scattering theory to a mass-operator formulation is given. A simple proof of the Poincaré invariance of the S operator that is obtained from a Bakamjian-Thomas model is also given.

The calculation of the critical exponent $\tau$ is crucial in the determination of critical phenomena in heavy ion reactions. This, however, is obscured by the unavoidable mixing of critical and noncritical events that results in nonclean signals. Here we report on a method to extract critical events from a set of mixed ones. In comparing to the traditional one, based on the so-called Campi plot, a distinct advantage is found.

The ${\beta }^{-}$ decay of ${}^{135}\mathrm{Sn}$ was studied for the first time yielding a half-life of 0.6(1) s and a partial level scheme for the ${\beta }^{-}$ decay to ${}^{135}\mathrm{Sb}.$ The ${}^{135}\mathrm{Sn}$ activity was produced at the mass separator OSIRIS via the fast neutron-induced fission of a ${}^{238}\mathrm{U}$ target inside a specially constructed ion source. ${}^{135}\mathrm{Sn}$ is the heaviest Sn isotope, for which spectroscopic results are presently determined. The new results are in disagreement with some of the theoretical predictions, which are used for modeling of the astrophysical r process.

It is shown that nuclear level densities in a finite space are described by a continuous binomial function, determined by the first three moments of the Hamiltonian, and the dimensionality of the underlying vector space. Experimental values for ${}^{55}\mathrm{Mn},$ ${}^{56}\mathrm{Fe},$ and ${}^{60}\mathrm{Ni}$ are very well reproduced by the binomial form, which turns out to be almost perfectly approximated by Bethe’s formula with backshift. A proof is given for which binomial densities reproduce the low moments of Hamiltonians of any rank: A strong form of the famous central limit result of Mon and French. Conditions under which the proof may be extended to the full spectrum are examined.

On the basis of shell model simulations, it is conjectured that the Lanczos construction at fixed quantum numbers defines—within fluctuations and behavior very near the origin—smooth canonical matrices whose forms depend on the rank of the Hamiltonian, dimensionality of the vector space, and second and third moments. A framework emerges that amounts to a general Anderson model capable of dealing with ground state properties and strength functions. The smooth forms imply binomial level densities. A simplified approach to canonical thermodynamics is proposed.

The density dependent hadron field theory, previously applied to isospin nuclei and hypernuclei is used to describe $\beta$-stable matter and neutron stars under consideration of the complete baryon octet. The meson-hyperon vertices are derived from Dirac-Brueckner calculations of nuclear matter and extended to hyperons. We examine properties of density dependent interactions derived from the Bonn A and from the Groningen nucleon-nucleon potential as well as phenomenological interactions. The consistent treatment of the density dependence introduces rearrangement terms in the expression for the baryon chemical potential. This leads to a more complex condition for the $\beta$ equilibrium compared to standard relativistic mean-field (RMF) approaches. We find a strong dependence of the equation of state and the particle distribution on the choice of the vertex density dependence. Results for neutron star masses and radii are presented. We find a good agreement with other models for the maximum mass. Radii are smaller compared to RMF models and indicate a closer agreement with results of nonrelativistic Brueckner calculations.

We provide a critical overview of the $\Phi$ measure of fluctuations and correlations. In particular we show that its discriminating power is rather limited in situations encountered in experiment.

The g factors of the $2_1^{+}$ and $4_1^{+}$ states in ${}^{78,80,82,84,86}\mathrm{Kr}$ have been measured for the first time, using Coulomb excitation of isotopic Kr beams and the transient field technique. The measured g factors of $2_1^{+}$ states in ${}^{78,80,82}\mathrm{Kr}$ are well described, in both magnitude and progression with neutron number, by the IBA-II model. Whereas the lighter isotopes show a dominant collective structure with g factor values close to $Z/A,$ the large ${g(2\mathrm{}}_1^{+})=1.12\mathrm{}(14)\mathrm{}$ value of ${}^{86}\mathrm{Kr},$ with its closed $N=50\mathrm{}$ shell, is unequivocally dominated by specific proton configurations. The g factor of the $2_1^{+}$ state in ${}^{84}\mathrm{Kr},$ with two holes in the ${1g}_{9/2}$ neutron orbit, reflects both proton and neutron components in the wave function. In addition, the lifetimes of several $2_1^{+}$ and $4_1^{+}$ states were remeasured by the Doppler shift attenuation method, yielding values which, in some cases, differ from those in the literature.

The structure of the three-dimension pressure-temperature-asymmetry surface of equilibrium of the asymmetric nuclear matter is studied within the thermal Thomas-Fermi approximation. Special attention is paid to the difference of the asymmetry parameter between the boiling sheet and that of the condensation sheet of the surface of equilibrium. We derive the condition of existence of the regime of retrograde condensation at the boiling of the asymmetric nuclear matter. We have performed calculations of the caloric curves in the case of isobaric heating. We have shown the presence of the plateau region in caloric curves at the isobaric heating of the asymmetric nuclear matter. The shape of the caloric curve depends on the pressure and is sensitive to the value of the asymmetry parameter. We point out that the experimental value of the plateau temperature $T\approx 7\hspace{0.5em}\mathrm{MeV}$ corresponds to the pressure ${P=10\mathrm{}}^{-2}\hspace{0.5em}{\mathrm{M}\mathrm{e}\mathrm{V}/\mathrm{f}\mathrm{m}}^3$ at the isobaric boiling.

We use the relativistic distorted wave impulse approximation to analyze data on ${}^{16}\mathrm{O}{(e,e}^{\prime }{p)}^{15}\mathrm{N}$ at $|Q^2|<~0.4\hspace{0.5em}(\mathrm{GeV}{/c)}^2$ that were obtained by different groups and seemed controversial. Results for differential cross sections, response functions, and $A_{\mathrm{TL}}$ asymmetry are discussed and compared to different sets of experimental data for proton knockout from $p_{1/2}$ and $p_{3/2}$ shells in ${}^{16}\mathrm{O}.$ We compare with a nonrelativistic approach to better identify relativistic effects. The present relativistic approach is found to accommodate most of the discrepancy between data from different groups, smoothing a long standing controversy.