Lifetimes have been measured in a superdeformed rotational band recently identified in the $N=Z$ nucleus ${}^{36}\mathrm{Ar}.$ A large low-spin quadrupole deformation $({\beta }_2=0.46\mathrm{}\pm 0.03)$ is confirmed and a decrease in the collectivity is observed as the high-spin band termination at $I^{\pi }{=16\mathrm{}}^{+}$ is approached. Detailed comparisons of the experimental $B\left(E2\mathrm{}\right)\mathrm{}$ values with the results of cranked Nilsson-Strutinsky and large-scale ${(s}_{1/2}{d}_{3/2})-\mathrm{pf}$ spherical shell model calculations indicate the need for a more refined treatment of transition matrix elements close to termination in the former, and the inclusion of the complete $\mathrm{sd}-\mathrm{pf}$ model space in the latter description of this highly-collective rotational band.

The multipolarities of the main transitions deexciting yrast isomers in ${}^{190}\mathrm{Pb}$ have been measured using conversion electron spectroscopy with pulsed beams. The enhanced $E3\mathrm{}$ character of the 407 keV transition from the ${11}^{-}$ isomer is confirmed and an independent value obtained for its lifetime. A new measurement of the properties of the 440 keV $E3\mathrm{}$ decay from the corresponding ${11}^{-}$ state in ${}^{192}\mathrm{Pb},$ has resulted in the identification of a new branch and a significantly different lifetime from that reported previously. The abnormally large strength of the ${11}^{-}$ to $8^{+}$ transitions in both ${}^{190}\mathrm{Pb}$ and ${}^{192}\mathrm{Pb}$ match those known in some light polonium isotopes, an effect which is suggested to be linked to a change in structure of the orbitals in the $8^{+}$ configuration when oblate deformation is established; the lowest $\Omega {=7/2\mathrm{}}^{-}$ proton Nilsson orbital changes from being predominantly of $h_{9/2}$ character at sphericity to a mixed $f_{7/2}{/h}_{9/2}$ parentage at oblate deformations, thus enabling an enhanced $i_{13/2}$ to $f_{7/2}$ octupole-coupled transition.

Calculations within the statistical multifragmentation model show that the neutron content of intermediate mass fragments can increase in the region of the liquid-gas phase transition in finite nuclei. The model predicts also inhomogeneous distributions of fragments and of their isospin in the freeze-out volume caused by angular momentum and an external long-range Coulomb field. These effects can take place in peripheral nucleus-nucleus collisions at intermediate energies and lead to neutron-rich isotopes produced in the midrapidity kinematic region.

We report the first measurement of the vector analyzing power in inclusive transversely polarized elastic electron-proton scattering at $Q^2=0.1\mathrm{}(\mathrm{GeV}{/c)}^2$ and large scattering angles. This quantity must vanish in the single virtual photon exchange, plane-wave impulse approximation for this reaction, and can therefore provide information on two photon exchange amplitudes for electromagnetic interactions with hadronic systems. The observable we have measured is driven by the imaginary part of the two photon exchange amplitude, the hadronic side of which is simply the Compton amplitude for the proton with two virtual photons. We find a small but nonzero value of $A=-15.4\pm 5.4$ ppm.

Measurements of the A dependence and pseudorapidity interval $\left(\delta \eta \right)$ dependence of midrapidity $E_T$ distributions in a half-azimuth (Δφ=π) electromagnetic calorimeter are presented for $p+\mathrm{Be},$ $p+\mathrm{Au},$ O+Cu, Si+Au, and Au+Au collisions at the BNL-AGS (Alternating-Gradient Synchrotron). The shapes of the upper edges of midrapidity $E_T$ distributions as a function of the pseudorapidity interval δη in the range 0.3 to 1.3, roughly centered at midrapidity, are observed to vary with δη, like multiplicity—the upper edges of the distributions flatten as δη is reduced. At the typical fixed upper percentiles of $E_T$ distributions used for nuclear geometry characterization by centrality definition—7 percentile, 4 percentile, 2 percentile, 1 percentile, 0.5 percentile—the effect of this variation in shape on the measured projectile $A_p$ dependence for ${}^{16}\mathrm{O},$ ${}^{28}\mathrm{Si},$ ${}^{197}$Au projectiles on an Au target is small for the ranges of δη and percentile examined. The $E_T$ distributions for $p+\mathrm{Au}$ and $p+\mathrm{Be}$ change in shape with δη; but in each δη interval the shapes of the $p+\mathrm{Au}$ and $p+\mathrm{Be}$ distributions remain indentical with each other—a striking confirmation of the absence of multiple-collision effects at midrapidity at AGS energies. The validity of the nuclear geometry characterization versus δη is illustrated by plots of the $E_T\left(\delta \eta \right)$ distribution in each δη interval in units of the measured $〈E_T\left(\delta \eta \right){〉}_{p+\mathrm{Au}}$ in the same δη interval for $p+\mathrm{Au}$ collisions. These plots, in the physically meaningful units of “number of average $p+\mathrm{Au}$ collisions,” are nearly universal as a function of δη, confirming that the reaction dynamics for $E_T$ production at midrapidity at AGS energies is governed by the number of projectile participants and can be well characterized by measurements in apertures as small as Δφ=π, δη=0.3.

The equilibration of hot and dense nuclear matter produced in the central cell of central Au+Au collisions at $\sqrt{s}=200A\mathrm{GeV}$ is studied within a microscopic transport model. The pressure in the cell becomes isotropic at $t\approx 5\mathrm{fm}/c$ after beginning of the collision. Within the next $15\mathrm{fm}/c$ the expansion of matter in the cell proceeds almost isentropically with the entropy per baryon ratio $S/A\cong 150,$ and the equation of state in the $(P,\varepsilon )$ plane has a very simple form, $P=0.15\mathrm{}\varepsilon .$ Comparison with the statistical model of an ideal hadron gas indicates that the time $t\approx 20\mathrm{fm}/c$ may be too short to reach the fully equilibrated state. Particularly, the creation of long-lived resonance-rich matter in the cell decelerates the relaxation to chemical equilibrium. This resonance-abundant state can be detected experimentally after the thermal freeze out of particles.

In this work we introduce a class of relativistic models for nuclear matter and neutron stars which exhibits a parametrization, through mathematical constants, of the nonlinear meson-baryon couplings. For appropriate choices of the parameters, it recovers current quantum hadrodynamics models found in the literature: the Walecka model and Zimanyi-Moszkowski models (ZM and ZM3). For other choices of parameters, the models give very interesting and new physical results. The phenomenology of neutron stars in ZM models is presented and compared to the phenomenology obtained in other versions of the Walecka model. We have found that the ZM3 model is too soft, and predicts a very small maximum neutron star mass, $\sim {0.72M}_{\odot }.$ A strong similarity between the results of ZM-like models and those with exponential couplings is noted. The sensibility of the results to the specific choice of the values for the binding energy and saturation density is pointed out. Finally, we discuss the very intense scalar condensates found in the interior of neutron stars, which may lead to negative effective masses.

Knowledge of the astrophysical rate of the ${}^{18}\mathrm{F}(p,\alpha {)}^{15}\mathrm{O}\mathrm{}$ reaction is important for understanding the γ-ray emission expected from novae and heavy-element production in x-ray bursts. The rate of this reaction is dominated at temperatures above $\sim 0.4$ GK by a resonance near 7.08 MeV excitation energy in ${}^{19}\mathrm{Ne}.$ The ${}^{18}\mathrm{F}(p,\alpha {)}^{15}\mathrm{O}$ rate has been uncertain in part because of disagreements among previous measurements concerning the resonance strength and excitation energy of this state. To resolve these uncertainties, we have made simultaneous measurements of the ${}^1\mathrm{H}{(}^{18}\mathrm{F}{,p)}^{18}\mathrm{F}$ and ${}^1\mathrm{H}{(}^{18}\mathrm{F},\alpha {)}^{15}\mathrm{O}$ excitation functions using a radioactive ${}^{18}\mathrm{F}$ beam at the ORNL Holifield Radioactive Ion Beam Facility. A simultaneous fit of the data sets has been performed, and the best fit was obtained with a center-of-mass resonance energy of $664.7\pm 1.6$ keV ${(E}_x=7076\mathrm{}\pm 2$ keV), a total width of $39.0\pm 1.6$ keV, a proton branching ratio of ${\Gamma }_p/\Gamma =0.39\mathrm{}\pm 0.02,$ and a resonance strength of $\omega \gamma =6.2\mathrm{}\pm 0.3$ keV.

Based on the self-adjoint extension theory mathematically rigorously defined two-body contact interaction in three dimension is reviewed. Local potential realizations of this proper contact interaction are given in terms of Pöschl-Teller, exponential, and square-well potentials. Three-body calculation is carried out for the halo nucleus ${}^{11}\mathrm{Li}$ using adequately represented contact interaction.

A detailed microscopic study of the temperature dependence of the shapes of some rare-earth nuclei is made in the relativistic mean field theory. Analyses of the thermal evolution of the single-particle orbitals and their occupancies leading to the collapse of the deformation are presented. The role of the nonlinear $\sigma$ field on the shape transition in different nuclei is also investigated; in its absence the shape transition is found to be sharper.

The first complete set of analyzing powers for any nuclear spin $\frac{3}{2}$ beam is reported. Analyzing powers and elastic cross section are presented for ${}^4\mathrm{He}{(}^7\mathrm{Li}\to {,}^7\mathrm{Li}{)}^4\mathrm{He}$ at the two center of mass energies of 11.5 and 16.5 MeV. An optical model analysis of these data shows the need for spin-orbit and second rank tensor potentials in addition to real and imaginary central potentials. The inclusion of triton transfer improves the description of the large angle elastic scattering cross section but has little impact on the calculated analyzing powers. The description of the third rank analyzing powers ${\mathrm{iT}}_{31}$ and ${\mathrm{iT}}_{33}$ is poor at small angles, and no combination of potentials including a large third rank potential is able to describe them. No real evidence for the presence of a third rank potential is found.

We examine the effects that a confining boundary together with hydrodynamical expansion play on two-pion distributions in relativistic heavy-ion collisions. We show that the effects arise from the introduction of further correlations due both to collective motion and the system’s finite size. As is well known, the former leads to a reduction in the apparent source radius with increasing average pair momentum K. However, for small K, the presence of the boundary leads to a decrease of the apparent source radius with decreasing K. These two competing effects produce a maximum for the effective source radius as a function of K.

Spectroscopic studies of neutrinoless double beta decays $\left(0\mathrm{}\nu \beta \beta \right)$ from ${}^{100}\mathrm{Mo}$ were made by means of ELEGANT V. The most stringent limits on the $0\nu \beta \beta$ half-lives were obtained for the ground state transitions $T_{1/2}^{0\nu }{(m}_{\nu })>\mathrm{}5.5\mathrm{}(10.3)\mathrm{}\times {10}^{22},$ $T_{1/2}^{0\nu }\left(\lambda \right)>\mathrm{}4.2\mathrm{}\left(8.5\right)\mathrm{}\times {10}^{22},$ and $T_{1/2}^{0\nu }\left(\eta \right)>\mathrm{}4.9\mathrm{}\left(9.3\right)\mathrm{}\times {10}^{22}\hspace{0.5em}\mathrm{yr},$ with 90(68)% C.L., for the mass term $〈m_{\nu }〉$ and for the right-handed weak current terms of $〈\lambda 〉$ and $〈\eta 〉,$ respectively. Using the nuclear matrix elements of the QRPA calculation by Tomoda et al., these limits lead to upper limits of $〈m_{\nu }〉<2.1\mathrm{}\left(1.5\right)\mathrm{}\hspace{0.5em}\mathrm{eV},$ $〈\lambda 〉<3.2\mathrm{}\left(2.5\right)\mathrm{}\times {10}^{-6},$ and $〈\eta 〉<2.4\mathrm{}\left(1.9\right)\mathrm{}\times {10}^{-8}$ with 90(68)% C.L. Limits on other terms beyond the standard theory are also discussed.

In high energy heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven and the Large Hadron Collider at CERN, each central event will contain multiple pairs of heavy quarks. If a region of deconfined quarks and gluons is formed, a mechanism for additional formation of heavy quarkonium bound states will be activated. This is a result of the mobility of heavy quarks in the deconfined region, such that bound states can be formed from a quark and an antiquark that were originally produced in separate incoherent interactions. Model estimates of this effect for $J/\psi$ production at RHIC indicate that significant enhancements are to be expected. Experimental observation of such enhanced production would provide evidence for deconfinement unlikely to be compatible with competing scenarios.

The methods currently used to measure azimuthal distributions of particles in heavy-ion collisions assume that all azimuthal correlations between particles result from their correlation with the reaction plane. However, other correlations exist, and it is safe to neglect them only if azimuthal anisotropies are much larger than $1/\sqrt{N},$ with N the total number of particles emitted in the collision. This condition is not satisfied at ultrarelativistic energies. We propose a new method, based on a cumulant expansion of multiparticle azimuthal correlations, which allows measurements of much smaller values of azimuthal anisotropies, down to $1/N.$ It is simple to implement and can be used to measure both integrated and differential flow. Furthermore, this method automatically eliminates the major systematic errors, which are due to azimuthal asymmetries in the detector acceptance.

The properties of thermal dilepton production from heavy-ion collisions in the RHIC energy regime are evaluated for invariant masses ranging from 0.5 to 3 GeV. Using an expanding thermal fireball to model the evolution through both quark-gluon and hadronic phases various features of the spectra are addressed. In the low-mass region, due to an expected large background, the focus is on possible medium modifications of the narrow resonance structures from $\omega$ and $\phi$ mesons, whereas in the intermediate-mass region the old idea of identifying QGP radiation is reiterated including effects of chemical undersaturation in the early stages of central Au+Au collisions.

A schematic study of the $\beta \beta 2\nu$ decay of ${}^{48}\mathrm{Ca}$ is made in a shell-model approach. The emphasis is especially put on the role of the spin-orbit potential in relation with the contribution of other terms in the strong interaction. This is discussed with a particular attention to the behavior of these ones under the SU(4) symmetry. Different methods in calculating the transition amplitude are also looked at with the aim to determine their reliability and, eventually, why they do not work. Further aspects relative to the failure of the operator expansion method to reproduce the results of more elaborate calculations are examined.

We consider the results of two proton transfer reactions, ${}^{10}\mathrm{B}{(}^7\mathrm{Be}{,}^8\mathrm{B}{)}^9\mathrm{Be}$ and ${}^{14}\mathrm{N}{(}^7\mathrm{Be}{,}^8\mathrm{B}{)}^{13}\mathrm{C},$ to obtain a weighted average of the measured asymptotic normalization coefficients for the virtual transition ${}^7\mathrm{Be}+p{\leftrightarrow }^8\mathrm{B}.$ These coefficients specify the amplitude of the tail of the ${}^8\mathrm{B}$ overlap function in the ${}^7\mathrm{Be}+p$ channel, and are used to calculate the astrophysical S factor for the direct capture reaction ${}^7\mathrm{Be}(p,\gamma {)}^8\mathrm{B}$ at solar energies, $S_{17}\mathrm{}\left(0\right).$ In light of recent improvements in the determination of optical-model potentials, including detailed understanding of the correlations between the DWBA analyses of the two experiments, and a new experimental measurement of the asymptotic normalization coefficients for the virtual transition ${}^{13}\mathrm{C}+p{\leftrightarrow }^{14}\mathrm{N},y$ we report a weighted average asymptotic normalization coefficient of $C_{p_{3/2}}^2=0.388\mathrm{}\pm 0.039\hspace{0.5em}{\mathrm{fm}}^{-1}$ for ${}^8\mathrm{B}\mathrm{}{\leftrightarrow }^7\mathrm{Be}+p,$ which implies $S_{17}\mathrm{}\left(0\right)=17.3\mathrm{}\pm 1.8$ eV b.

With Wigner’s SU(4) supermultiplet symmetry [and its generalization to pseudo-SU(4)] as a starting point, a boson-model space is constructed that includes $T=0\mathrm{}$ as well as $T=1\mathrm{}$ bosons (interacting boson model-4). The boson Hamiltonian is derived microscopically from a realistic shell-model interaction through a mapping that relies on the existence of approximate shell-model symmetries. Applications are presented for odd-odd $N=Z$ nuclei from ${}_{29}^{58}{\mathrm{Cu}}_{29}$ to ${}_{35}^{70}{\mathrm{Br}}_{35}.$

The transition strength for Coulomb breakup of ${}^6\mathrm{He}$ into ${}^4\mathrm{He}+n+n$ three-body unbound states is studied in the framework of the complex scaling method (CSM). We propose a method to analyze the three-body unbound states in which CSM is utilized to decompose the three-body transition strengths into resonance and continuum components. We calculate the contributions of $E1\mathrm{}$ and $E2\mathrm{}$ transitions, not only from three-body resonances, but also from two-body ${\mathrm{“}}^5\mathrm{He}+n\mathrm{”}$ and three-body ${\mathrm{“}}^4\mathrm{He}+n+n\mathrm{”}$ continuum states. From the calculated strength distributions, we discuss the characteristic structures of ${}^6\mathrm{He}$ in the positive energy region, and also the Coulomb breakup mechanism of ${}^6\mathrm{He}.$ We show that the two-body ${\mathrm{“}}^5\mathrm{He}+n\mathrm{”}$ component is dominant in the total Coulomb breakup cross section.