$\alpha$-particle decays from several excited states in ${}^{11}\mathrm{C}$, ${}^{13}\mathrm{C}$, and ${}^{15}\mathrm{N}$ have been observed in three-body final state reactions induced by heavy-ion beams at 6.5–9.0 MeV/nucleon from the FSU Tandem/LINAC. Where possible, branching fraction estimates are made. Improvements in the energy resolution of the detection system have allowed the observation of many previously unreported $\alpha$-particle decays, several new total energy width determinations, and a few new excited state energies.

The general structure of the cross section of $\gamma N$ scattering with polarized photon and/or nucleon in initial and/or final state is systematically described and exposed through invariant amplitudes. A low-energy expansion of the cross section up to and including the order $\mathcal{O}\left({\omega }^4\right)$ is given that involves ten structure parameters of the nucleon (dipole, quadrupole, dispersion, and spin polarizabilities). Their physical meaning is discussed in detail. Using fixed-$t$ dispersion relations, predictions for these parameters are obtained and compared with results of chiral perturbation theory. It is emphasized that Compton scattering experiments at large angles can fix the most uncertain of these structure parameters. Predictions for the cross section and double-polarization asymmetries are given and the convergence of the expansion is investigated. The feasibility of the experimental determination of some of the structure parameters is discussed.

We investigate the Coulomb part of the one-neutron removal cross section in breakup reactions of the neutron rich nuclei ${}^{11}\mathrm{Be}$ and ${}^{19}\mathrm{C}$. Approximate Coulomb breakup amplitudes are derived from two distinct theoretical viewpoints. One of these uses an approximation to the distorted-wave Born approximation. The other assumes an adiabatic treatment of the projectile excitation to the low energy continuum. Both approaches include approximately the finite range of the interaction between the breakup fragments and so can treat non-$s$-wave projectiles. Calculations are analyzed and compared with available experimental data for total one-neutron removal cross sections, neutron angular distributions, heavy charged fragment momentum distributions, and excitation energy spectra for breakup on high $Z$ targets.

A systematic study of the influence of exchange terms in the longitudinal and transverse nuclear response to quasielastic ${(e,e}^{\prime })$ reactions is presented. The study is performed within the framework of the extended random phase approximation, which in conjuction with a projection method permits a separation of various contributions tied to different physical processes. The calculations are performed in nuclear matter up to second order in the residual interaction for which we take a $(\pi +\rho )$ model with the addition of the Landau-Migdal $g^{\prime }$ parameter. Exchange terms are found to be important only for the random-phase-approximation-type contributions around the quasielastic peak.

We use the generator coordinate method (GCM) to define multicluster wave functions of the $\alpha +(p+n)\mathrm{}$ system. Distortion effects of the deuteron are included through a mixing of several $p+n$ configurations. The model is tested on the ${}^6\mathrm{Li}$ spectroscopy, and on the $\alpha +p$ and $\alpha +d$ elastic phase shifts. The comparison with experiment gives a fairly good agreement in all the cases. At low temperatures, we predict a reduction by a factor of 10 of the ${}^2\mathrm{H}(\alpha ,\gamma {)}^6\mathrm{Li}$ reaction rate, with respect to astrophysics compilations. The GCM cross section is also used to test the validity of the extranuclear approximation.

The process of light particle evaporation moves the position of an excited fragment in the chart of nuclides towards a line which will be called the evaporation attractor line. The predicted location of this line is parametrized and the conditions necessary for the secondary fragment distributions to reach this line are discussed.

We calculate the momentum dependence of the $\rho$-meson self-energy based on the dispersion relation for the $\rho N$ scattering amplitude $f\left(\omega \right)$ at low nuclear density. The imaginary part of $f\left(\omega \right)$ is determined from the optical theorem, while the total $\rho N$ cross section is obtained within the vector dominance model at high energy and within the resonance model at low energy. Our numerical results indicate a sizable broadening of the $\rho$-meson width in the medium especially for low relative momenta $p$ while the real part of the $\rho$ self-energy is found to change its sign and to become repulsive already at momenta above $100\hspace{0.5em}\mathrm{MeV}/c.\mathrm{}$ Extrapolating to nuclear saturation density ${\rho }_0$ we find a dropping of the $\rho$ mass for $p\approx \hspace{0.5em}0$ roughly in line with the QCD sum rule analysis of Hatsuda while at high energy an increase of the $\rho$ mass close to the prediction by Eletsky and Ioffe is obtained. However, when including a broadening of the baryonic resonances in the medium, the $\rho$-meson mass shift at $p\approx 0$ becomes slightly repulsive, whereas the width increases substantially.

For the photoproduction of vector mesons, all single and double spin observables involving vector-meson two-body decays are defined consistently in the $\gamma N$ center-of-mass frame. These definitions yield a procedure for extracting physically meaningful single and double spin observables that are subject to known rules concerning their angle and energy evolution. As part of this analysis, we show that measuring the two-meson decay of a photoproduced $\rho$ or $\phi$ does not determine the vector meson’s vector polarization, but only its tensor polarization. The vector meson decay into lepton pairs is also insensitive to the vector meson’s vector polarization, unless one measures the spin of one of the leptons. Similar results are found for all double spin observables which involve observation of vector-meson decay. To access the vector meson’s vector polarization, one therefore needs to either measure the spin of the decay leptons, make an analysis of the background interference effects, or relate the vector meson’s vector polarization to other accessible spin observables.

We present calculations of the momentum dependence of generalized electric, magnetic, and spin-dependent polarizabilities of the proton in virtual Compton scattering in an effective Lagrangian model which includes the nucleon, $\pi ,$ $\sigma ,$ $\rho ,$ and $\omega$ mesons, and baryon resonances with masses up to 1.7 GeV. The model describes simultaneously pion-nucleon scattering phase shifts, pion photoproduction multipoles, and Compton scattering cross sections. The unitarity within the channel space $\pi N\oplus \gamma N$ is achieved in the $K$-matrix approach. The different contributions to the generalized polarizabilities are studied.

The ALADIN data for the disassembly of projectile remnants in Au+Au reactions at $600A\hspace{0.5em}\mathrm{MeV}$ are investigated using a simple dynamics and statistics model. Once the model parameter relevant to the excitation energy is fixed via fitting one datum point in the experimental correlation curve between the mean multiplicity of IMF and the $Z_{\mathrm{bound}},$ not only this full correlation curve but also all the experimental charge correlations are reproduced nicely. The data of the size of projectile remnant and of the excitation energy per nucleon as functions of $Z_{\mathrm{bound}}$ are reproduced as well. Meanwhile, the theoretical relative yield of the decay mode of projectile remnant as a function of $Z_{\mathrm{bound}}$ is comparable with the experimental ones. In addition, the theoretical caloric curve of projectile remnants is also similar to the ALADIN ones. However, it is premature to conclude that the ALADIN caloric curve is relating to the liquid-gas phase transition.

We develop a formalism to study the influence of the breakup process of a weakly bound projectile on the complete fusion cross section. We show that the complete fusion and the resulting incomplete fusion cross sections can be expressed in terms of breakup and survival probabilities, which are evaluated with the help of appropriate polarization potentials. The effects of the finite size of the projectile and of Fermi motion are estimated. As examples, we consider light–heavy-ion collisions where threshold effects play an interesting role.

A nucleon-nucleus optical model potential (OMP) is built from the nuclear matter (NM) approach of Jeukenne, Lejeune, and Mahaux (JLM). The imaginary component of the on-shell NM mass operator, originally parametrized by these authors as a function of matter density and energy, is given a new representation suitable for energies from 1 to 200 MeV. The JLM model extended in this manner is then applied through an improved local density approximation (LDA) to treat nucleon scattering from closed- and near closed-shell nuclei with masses $40<~A<~209$. For proton, neutron, and charge radial densities, we use those obtained from Hartree-Fock-Bogoliubov calculations based on the finite range, density dependent Gogny force. Several LDA and spin-orbit potential prescriptions are tested to select those which provide the best overall description of elastic scattering and reaction measurements. Over three hundred datasets including differential cross sections, analyzing powers, spin rotation functions, and reaction cross sections are considered in the present analyses. The OMP components include normalization factors which are optimized for each incident energy, probe, and for most target nuclei. We give close forms which represent the energy variation of these factors for the $n+X$ and $p+X$ systems. The global OMPs built in this manner produce a good overall description of the neutron and proton scattering and reaction measurements available up to 200 MeV.

The photon multiplicity has been measured for the first time in S+Au collisions at $200A$ GeV over a wide pseudorapidity range $(2.8\mathrm{}<~\eta <~5.2)$ employing a fine granularity preshower detector. The pseudorapidity density of photons increases with centrality, reaching $\sim 200$ at the highest centrality studied. The results are compared with measurements of the charged particle multiplicity and with predictions of the VENUS event generator.

We have measured the yields of protons and $A=2\mathrm{}–4$ nuclei in collisions between $10.8A\mathrm{GeV}/c$ Au beams and targets of Al, Cu, and Au. The data, which cover a broad rapidity range at low transverse momenta, were measured as a function of collision centrality using a focusing beam line spectrometer and a high-rate centrality detector. We investigate the dependence of coalescence parameters on event geometry. The data are compared with the predictions of an RQMD+coalescence model.

We describe some detailed numerical simulations of disoriented chiral condensates (DCC's), using the chiral Lagrangian as a controlled long-wavelength description. We focus on the possibility of multiple, independently coherent domains, and investigate the degree to which the DCC signal is attenuated. As an intermediate step in our analysis we compute the expected number of detector events in each isospin and momentum channel for a given asymptotic classical field configuration. We find that for sufficiently large initial field strengths, the nonlinear interactions between domains become important and can lead to a randomization of isospin orientations. Nevertheless, we argue that viable signals exist for DCC detection, even in the case of multiple domains and strong domain-domain interactions. We briefly discuss some long-lived “pseudobound-state” configurations which arise at large field strengths and might be observable in Hanbury-Brown-Twiss correlations.

We develop two further numerical tests of parton cascade models: the ideal gas equation of state and the collision frequency tests. The equation of state test checks the initial momentum distribution generator and free expansion dynamics in periodic inhomogeneous geometries. The collision rate test is sensitive to spatial inhomogeneities and the collision algorithm. These tests are applied to the recently developed ZPC parton cascade model. The tests helped uncover unphysical correlations induced by one of the commonly used random number generators and showed the necessity of particle subdivisions for convergence to the exact analytic limit.

Deviation of the multiplicity distribution $P_q$ in a small bin from its Poisson counterpart $p_q$ is studied within the Ginzburg-Landau description for a second-order quark-hadron phase transition. The dynamical factor $d_q\equiv P_q{/p}_q$ for the distribution and the ratio $D_q\equiv d_q{/d}_1$ are defined, and novel scaling behaviors between $D_q$ are found which can be used to detect the formation of quark-gluon plasma. The study of $d_q$ and $D_q$ is also very interesting for other multiparticle production processes without a phase transition.

The strongly interacting matter under extreme conditions of temperature for the conjectured deconfined phase of the quark-gluon plasma is investigated. A systematic study of the form of the thermal ratio of the disorder deviation (TRDD) is presented with the emphasis on the degree of deviation of the TRDD function from unity. The space-time evolution of quarks and gluons is studied in the framework of two-particle correlation functions to predict the space-time size of the closed deconfined phase.

It is shown in this paper that the vacuum configuration of the bilocal field in the global color symmetry model (GCM) can be calculated in the instanton dilute liquid approximation. As only the excitation of Goldstone bosons is taken into account, the relative motion against the vacuum is equivalent to the dynamical mass of a quark. The bilocal field generating the mesons $\pi$ and $\sigma$ in the GCM is then determined. With the determined bilocal field and the effective action, the masses and the decay constants of the mesons $\pi$ and $\sigma ,$ and the decay width of $\overrightarrow{\sigma }\pi \pi$ are calculated in the GCM. The calculated results agree with experimental data quite well.

We present a coupled channel partial wave analysis of nondiffractive $S$-wave ${\pi }^{+}{\pi }^{-}$ and $K^{+}{K}^{-}$ photoproduction focusing on the $K\overline{K}$ threshold. Final state interactions are included. We calculate total cross sections and angular and effective mass distributions in both $\pi \pi$ and $K\overline{K}$ channels. Our results indicate that these processes are experimentally measurable and valuable information on the $f_0$(980) resonance structure can be obtained.