Results on charged pion and kaon production in central $\mathrm{Pb}+\mathrm{Pb}$ collisions at $20A$ and $30A$ GeV are presented and compared to data at lower and higher energies. Around $30A$ GeV a rapid change of the energy dependence for the yields of pions and kaons as well as for the shape of the transverse mass spectra is observed. The change is compatible with the prediction that the threshold for production of a state of deconfined matter at the early stage of the collisions is located at low CERN Super Proton Synchroton energies.

We study the side-ward and elliptic differential flow of protons and charged pions for Pb+Pb collisions at $40A$ GeV and $158A$ GeV energies in a microscopic relativistic transport simulation model. The calculation of flow results are compared with the recent data from the NA49 Collaboration as a function of transverse momenta, rapidity, and centrality. It is found that in the simulation model without potential explains the side-ward flow qualitatively well and with potential favors the elliptic flow reasonably good with the experimental data.

We apply a quark model developed in earlier work to the spectrum of baryons with strangeness $-2$ and $-3$. The model describes a number of well-established baryons successfully, and application to cascade baryons allows the quantum numbers of some known states to be deduced. [JLAB-THY-07-728]

Low-momentum two-nucleon interactions obtained with the renormalization group method and the similarity renormalization group method are used to study the cutoff dependence of low-energy $3N$ and $4N$ scattering observables. The residual cutoff dependence arises from omitted short-ranged $3N$ (and higher) forces that are induced by the renormalization group transformations and may help to estimate the sensitivity of various $3N$ and $4N$ scattering observables to short-ranged many-body forces.

Fission fragment mass-angle correlations and mass ratio distributions have been measured for the reactions ${}^{16}\mathrm{O}+{}^{186}\mathrm{Os}$, ${}^{24}\mathrm{Mg}+{}^{178}\mathrm{Hf}$, ${}^{34}\mathrm{S}+{}^{168}\mathrm{Er}$, and ${}^{48}\mathrm{Ti}+{}^{154}\mathrm{Sm}$, forming the ${}^{202}\mathrm{Po}$ composite nucleus, at near barrier energies. Systematic analysis based on the expected dependence of the variance of the mass distribution on the angular momentum and temperature of the compound nucleus indicate that the two lighter systems evolve through true compound nucleus fission. Evidence of quasifission was observed for the two most mass-symmetric reactions, through strong mass-angle correlations for the ${}^{48}\mathrm{Ti}+{}^{154}\mathrm{Sm}$ reaction and a broadened mass ratio distribution for the ${}^{34}\mathrm{S}+{}^{168}\mathrm{Er}$ reaction. Furthermore, the increase in mass width at near barrier energies shows the influence of the alignment of statically deformed target nuclei.

Charged-particle decay from the dipole resonances at $E_x=24$ MeV in ${}^6\mathrm{He}$ and at $E_x=18$ MeV in ${}^7\mathrm{He}$ was studied via the ${}^{6,7}\mathrm{Li}$(${}^7\mathrm{Li}$,${}^7\mathrm{Be}$ $x$) coincidence experiment at 455 MeV and at $0^{°}$. These resonances are those that were interpreted as the analogs of the dipole resonances in the α clusters of ${}^6\mathrm{Li}$ and ${}^7\mathrm{Li}$ in our previous work. The dominant decay channels (branching ratios) of the dipole resonances are found to be $d+t+n$ ($26~32\%$) and $\alpha +2n$ ($47~69\%$) for ${}^6\mathrm{He}$ and $t+t+n$ ($47~55\%$) and $\alpha +3n$ ($38~47\%$) for ${}^7\mathrm{He}$. The branching ratios measured for the $d+t+n$ and $t+t+n$ channels in ${}^6\mathrm{He}$ and ${}^7\mathrm{He}$, respectively, are larger than those calculated in a simple statistical model by a factor of $~100$. These results are consistent with the picture that the observed dipole resonances are analogs of the corresponding dipole resonances in the α clusters of ${}^6\mathrm{Li}$ and ${}^7\mathrm{Li}$.

We calculate the $s$-wave part of the pion-nucleus optical potential using a unitarized chiral approach that has been previously used to simultaneously describe pionic hydrogen and deuterium data as well as low-energy $\pi N$ scattering in vacuum. This energy-dependent model allows for additional isoscalar parts in the potential from multiple rescattering. We consider Pauli blocking and pion polarization in an asymmetric nuclear matter environment. Also, higher order corrections of the $\pi N$ amplitude are included. The model can accommodate the repulsion required by phenomenological fits, though the theoretical uncertainties are bigger than previously thought. We also find an enhancement of the isovector part compatible with empirical determinations.

The diffusion of a particle passing over the saddle point of a two-dimensional quadratic potential is studied via a set of coupled Langevin equations, and the expression for the passing probability is obtained exactly. The passing probability is found to be strongly influenced by the off-diagonal components of inertia and friction tensors. If the system undergoes the optimal path to pass over the saddle point by taking an appropriate direction of initial velocity into account, which departs from the potential valley and has minimum dissipation, the passing probability should be enhanced. Applying this to the fusion of massive nuclei, we show that there exists an optimal injection choice for the deformable target and projectile nuclei, namely, the intermediate deformation between spherical and extremely deformed nuclei, that maximizes the fusion probability.

An analytical recursive formula of the partial-wave scattering matrix for the total effective complex potential of nucleus-nucleus collisions is derived to conveniently analyze the data of angular variations of elastic scattering cross sections. Further, another expression of cross sections for the absorption from arbitrarily small intervals is derived. This leads to the explanation of the fusion cross section (${\sigma }_{\mathrm{fus}}$) data at various incident center-of-mass energies $E_{\mathrm{c}.\mathrm{m}.}$ by collecting the absorption contributions in the interior region of the effective potential. This concept is akin to that used by Udagawa et al. in the calculation of fusion cross sections in elastic channels. The interaction potential considered in the analysis is energy independent and by virtue of its weakly absorbing character it supports resonance states in different partial-wave trajectories. Consequently, occurrence of these resonances is shown to be the physical origin of the observed oscillatory structure in the variation respect to energy of the quantity $D(E_{\mathrm{c}.\mathrm{m}.})=d^2(E_{\mathrm{c}.\mathrm{m}.}{\sigma }_{\mathrm{fus}})/{\mathit{dE}}_{\mathrm{c}.\mathrm{m}.}^2$, the second derivative of the product $E_{\mathrm{c}.\mathrm{m}.}{\sigma }_{\mathrm{fus}}$ with respect to $E_{\mathrm{c}.\mathrm{m}.}$. In this article, we investigate two well-known cases of heavy-ion collisions, namely ${}^{12}\mathrm{C}+{}^{208}\mathrm{Pb}$ and ${}^{16}\mathrm{O}+{}^{208}\mathrm{Pb}$, and obtain simultaneous and very successful explanations of cross sections for elastic scattering and fusion and the results of $D(E_{\mathrm{c}.\mathrm{m}.})$. These results obtained by using a somewhat novel and convenient method demonstrate the unified description of scattering and fusion for interacting heavy-ion systems.

Data on elastic scattering of 96 MeV neutrons from ${}^{56}\mathrm{Fe}$, ${}^{89}\mathrm{Y}$, and ${}^{208}\mathrm{Pb}$ in the angular interval $10\text{−}{70}^{°}$ are reported. The previously published data on ${}^{208}\mathrm{Pb}$ have been extended, as a new method has been developed to obtain more information from data, namely to increase the number of angular bins at the most forward angles. A study of the deviation of the zero-degree cross section from Wick's limit has been performed. It was shown that the data on ${}^{208}\mathrm{Pb}$ are in agreement with Wick's limit while those on the lighter nuclei overshoot the limit significantly. The results are compared with modern optical model predictions, based on phenomenology and microscopic nuclear theory. The data on ${}^{56}\mathrm{Fe}$, ${}^{89}\mathrm{Y}$, and ${}^{208}\mathrm{Pb}$ are in general in good agreement with the model predictions.

We study the hadron-quark phase transition in the interior of neutron stars. The relativistic mean field (RMF) theory is adopted to describe the hadronic matter phase, while the Nambu-Jona-Lasinio (NJL) model is used for the quark matter phase. The influence of the hadronic equation of state on the phase transition and neutron star properties are investigated. We find that a neutron star possesses a large population of hyperons, but it is not dense enough to possess a pure quark core. Whether the mixed phase of hadronic and quark matter exist in the core of neutron stars depends on the RMF parameters used.

We study the evolution and saturation of the gluon distribution function in the quark-gluon plasma as probed by a propagating parton and its effect on the computation of jet quenching or transport parameter $\widehat{q}$. For thermal partons, the saturation scale $Q_s^2$ is found to be proportional to the Debye screening mass ${\mu }_D^2$. For hard probes, evolution at small $x=Q_s^2/6\mathit{ET}$ leads to jet energy dependence of $\widehat{q}$. We study this dependence both for a conformal gauge theory in weak and strong coupling limit and for (pure gluon) QCD. The energy dependence can be used to extract the shear viscosity η of the medium, since η can be related to the transport parameter for thermal partons in a transport description. We also derive upper bounds on the transport parameter for both energetic and thermal partons. The latter leads to a lower bound on the shear viscosity to entropy density ratio which is consistent with the conjectured lower bound $\eta /s⩾1/4\pi$. We also discuss the implications of these results on the study of jet quenching at the BNL Relativistic Heavy Ion Collider and the CERN Large Hadron Collider and the bulk properties of the dense matter.

A group theoretic method for the systematic study of multiquark states is developed. The calculation of matrix elements of many-body Hamiltonians is simplified by transforming the physical bases (quark cluster bases) to symmetry bases (group chain classified bases), where the fractional parentage expansion method can be used. A five-quark system is taken as the example in this study. The Jaffe–Wilczek $\mathit{qq}\text{−}\mathit{qq}\text{−}\overline{q}$ configuration is chosen as one of the examples to construct the physical bases and the transformation coefficients between physical bases and symmetry ones are shown to be related to the ${\mathrm{SU}}_{\mathit{mn}}\supset {\mathrm{SU}}_m\times {\mathrm{SU}}_n$ isoscalar factors. A complete transformation coefficient table is obtained. The needed isoscalar factors and fractional parentage coefficients have been calculated with our new group representation theory and published before. Three quark models, the naive Glashow-Isgur model, the Salamanca chiral quark model, and quark delocalization color screening model, are used to show the general applicability of the new multiquark calculation method and general results of constituent quark models for five-quark states are given.

We report new shell-model calculations of the isospin-symmetry-breaking correction ${\delta }_C$ to superallowed $0^{+}\to 0^{+}$ nuclear β decay. The most important improvement is the inclusion of core orbitals, which are demonstrated to have a significant impact on the mismatch in the radial wave functions of the parent and daughter states. We determine which core orbitals are important to include from an examination of measured spectroscopic factors in single-nucleon pickup reactions. In addition, where new sets of effective interactions have become available since our last calculation, we now include them; this leads to small changes in ${\delta }_{\mathrm{NS}}$ as well. We also examine the new radiative-correction calculation by Marciano and Sirlin and, by a simple reorganization, show that it is possible to preserve the conventional separation into a nucleus-independent “inner” radiative term, ${\Delta }_R^V$, and a nucleus-dependent “outer” term, ${\delta }_R^{\text{'}}$. We tabulate the new values for ${\delta }_C,{\delta }_{\mathrm{NS}}$, and ${\delta }_R^{\text{'}}$ for 20 superallowed transitions, including the 13 currently well-studied cases. With these new correction terms, the corrected $\mathcal{F}t$ values for the 13 cases are statistically consistent with one another, and the anomalousness of the ${}^{46}\mathrm{V}$ result disappears. These new calculations lead to a lower average $\overline{\mathcal{F}t}$ value and a higher value for $V_{\mathrm{ud}}$. The sum of squares of the top-row elements of the Cabibbo-Kobayashi-Maskawa matrix now agrees exactly with unitarity.

We correct a mistake in the analytical expression for the energy density given in Phys. Rev. C 76, 021902 (2007). The expression should be multiplied by a factor 16. This factor manifests a subtle problem in the treatment of the random color distribution in the longitudinal extent.

A high-spin rotational band was observed in the $N=90$ nucleus ${}^{160}\mathrm{Yb}$ with moment of inertia and decay characteristics very similar to recently discovered sequences in ${}^{157,158}\mathrm{Er}$. These latter structures were discussed in terms of strongly deformed triaxial bands. Detailed cranked Nilsson-Strutinsky calculations were performed that predict that well-deformed triaxial structures are also expected at high spin in ${}^{160}\mathrm{Yb}$. Within this interpretation the observed discontinuity in the dynamic moment of inertia around $\hslash \omega =0.40\text{−}0.45$ MeV can be explained as a crossing between $i_{13/2}$ neutron levels.

We derive general expressions for non-energy-weighted and energy-weighted cluster sum rules for systems of three charged particles. The interferences between pairs of particles are found to play a substantial role. The energy-weighted sum rule is usually determined by the kinetic energy operator, but we demonstrate that it has similar additional contributions from the angular momentum and parity dependence of two- and three-body potentials frequently used in three-body calculations. The importance of the different contributions is illustrated with the dipole excitations in ${}^6\mathrm{He}$. The results are compared with the available experimental data.

Charm production from the quark-gluon plasma created in the midrapidity of central heavy ion collisions at the Large Hadron Collider (LHC) is studied in the next-to-leading order in QCD. Using a schematic longitudinally boost-invariant and transversally expanding fire-cylinder model, we find that charm production could be appreciably enhanced at LHC as a result of the high temperature that is expected to be reached in the produced quark-gluon plasma. Sensitivities of our results to the number of charm quark pairs produced from initial hard scattering, the initial thermalization time and temperature of the quark-gluon plasma, and the charm quark mass are also studied.

We demonstrate the existence of multiple converging sequences in the ab initio no-core shell model. By examining the underlying theory of effective operators, we expose the physical foundations for the alternative pathways to convergence. This leads us to propose a revised strategy for evaluating effective interactions for $A$-body calculations in restricted model spaces. We suggest that this strategy is particularly useful for applications to nuclear processes in which states of both parities are used simultaneously, such as for transition rates. We demonstrate the utility of our strategy with large-scale calculations in light nuclei.