The newly discovered exotic $\Theta$ baryon of mass $1540\mathrm{MeV}$ (and very small width) truly has a very low mass, if it is a pentaquark system of even parity. A schematic model in which the coherent interaction of $u\overline{s}$ and $d\overline{s}$ pairs leads to a very large residual attractive interaction is introduced. This collective vibrational model accounts for the mass and small decay width to the $KN$ channel, but yields a significant coupling to the virtual $K*N$ channel. The schematic model predicts an attractive $\Theta$-nucleon interaction sufficient to produce a $\Theta$-nuclear bound state stable against strong decays. The discovery of $\Theta$-nuclei could be a proof that the $\Theta$ parity is even.

We study the local dynamic polarization potential, DPP, component of the ${}^6\mathrm{He}+{}^{208}\mathrm{Pb}$ interaction generated by the coupling to breakup channels as calculated using the continuum-discretized coupled-channels (CDCC) method. The results are for ${}^6\mathrm{He}$ at a laboratory energy of $27\mathrm{MeV}$. The elastic channel $S$-matrix is inverted and the bare potential of the CDCC calculation is subtracted to yield the DPP. This has a very long attractive and absorptive tail, with the real component extending beyond $40\mathrm{fm}$, generated by Coulomb breakup. Although the long tail of the DPP has a major effect on the elastic $S$-matrix, it is shallow enough to have a more modest effect on the root mean square (rms) radius (increased) and the volume integrals. To facilitate comparison with other theories, the potential tails are fitted to analytic forms.

A large number of precision fusion excitation functions, at energies above the average fusion barriers, have been fitted using the Woods-Saxon form for the nuclear potential in a barrier passing model of fusion. They give values for the empirical diffuseness parameter $a$ ranging between 0.75 and $1.5\mathrm{fm}$, compared with values of about $0.65\mathrm{fm}$ which generally reproduce elastic scattering data. There is a clear tendency for the deduced $a$ to increase strongly with the reaction charge product $Z_1{Z}_2$, and some evidence for the effect of nuclear structure on the value of $a$, particularly with regard to the degree of neutron richness of the fusing nuclei, and possibly with regard to deformation. The measured fusion-barrier energies are always lower than those of the bare potentials used, which is expected as a result of adiabatic coupling to high energy collective states. This difference increases with increasing $Z_1{Z}_2$ and calculations show that about $1∕3$ of it may be attributed to coupling to the isoscalar giant-quadrupole resonances in the target and projectile. Coupling to all giant resonances may account for a significant part. Fluctuations about the trend line may be due to systematic errors in the data and/or structure effects such as coupling to collective octupole states. Previously suggested reasons for the large values of $a$ have been related to departures from the Woods-Saxon potential and to dissipative effects. This work suggests that the apparently large values of $a$ may be an artifact of trying to describe the dynamical fusion process by use of a static potential. Another partial explaination might reside in fusion inhibition, due for example to deep-inelastic scattering, again a process requiring dynamical calculations.

We develop the notion of shower partons and determine their distributions in jets in the framework of the recombination model. The shower parton distributions obtained render a good fit of the fragmentation functions. We then illustrate the usefulness of the distributions in a problem where a jet is produced in the environment of thermal partons as in heavy-ion collisions. The recombination of shower and thermal partons is shown to be more important than fragmentation. Application to the study of two-particle correlation in a jet is also carried out.

A formalism for hadron production at high $p_T$ in heavy-ion collisions has been developed such that all partons hadronize by recombination. The fragmentation of a hard parton is accounted for by the recombination of shower partons that it creates. Such shower partons can also recombine with the thermal partons to form particles that dominate over all other possible modes of hadronization in the $3<p_T<8\mathrm{GeV}$ range. The results for the high $p_T$ spectra of pion, kaon, and proton agree well with experiments. Energy loss of partons in the dense medium is taken into account on the average by an effective parameter by fitting data, and is found to be universal independent of the type of particles produced, as it should. Due to the recombination of thermal and shower partons, the structure of jets produced in nuclear collisions is different from that in $pp$ collisions. The consequence on same-side correlations is discussed.

We calculate the equation of state of a quark system interacting through a phenomenological potential, the Richardson’s potential, at finite baryon density and zero temperature. In particular we study three different cases with different quark masses ($u$ and $d$), and different assumptions for the potential at large distances. We solve molecular dynamics with a constraint due to Pauli blocking and find evidence of a phase transition from “nuclear” to “quark matter.” The phase transition is analyzed also through the behavior of the $J∕\Psi$ embedded in the quark system. We show that the $J∕\Psi$ particle behaves as an order parameter.

The angular distribution of the reaction ${}^6\mathrm{Li}(d,\alpha ){}^4\mathrm{He}$ at deuteron energies below $100\mathrm{keV}$ and the total cross section as well as the angular distribution of the reaction ${}^{10}\mathrm{B}(d,p_0){}^{11}\mathrm{B}$ at energies below $350\mathrm{keV}$ have been measured. Based on our experimental results and data of other authors, the reaction mechanism has been studied in a wide energy range, relevant for astrophysical applications. It has been found that in both cases broad resonances in the compound nuclei play the key role for the description of the excitation functions. The long-standing problems of describing the angular distributions could be solved for both reactions by assuming a coherent superposition between resonant and direct reaction amplitudes. A theoretical approach allowing for coherent calculations has been developed. Some astrophysical implications are discussed.

In this work we evaluate the ${}^{1}S_0$ energy gap of ${\Sigma }^{-}$ hyperons in $\beta$-stable neutron star matter. We solve the BCS gap equation for an effective ${\Sigma }^{-}{\Sigma }^{-}$ pairing interaction derived from the most recent parametrization of the hyperon-hyperon interaction constructed by the Nijmegen group. We find that the ${\Sigma }^{-}$ hyperons are in a ${}^{1}S_0$ superfluid state in the density region $\sim 0.27–0.7{\mathrm{fm}}^{-3}$, with a maximum energy gap of order $8\mathrm{MeV}$ at a total baryon number density of $\sim 0.37{\mathrm{fm}}^{-3}$ and a ${\Sigma }^{-}$ fraction of about 8%. We examine the implications on neutron star cooling.

We carry out Faddeev calculations of three-alpha $\left(3\alpha \right)$ and two-alpha plus $\Lambda$ $\left(\alpha \alpha \Lambda \right)$ systems, using two-cluster resonating-group method kernels. The input includes an effective two-nucleon force for the $\alpha \alpha$ resonating-group method and a new effective $\Lambda N$ force for the $\Lambda \alpha$ interaction. The latter force is a simple two-range Gaussian potential for each spin-singlet and triplet state, generated from the phase-shift behavior of the quark-model hyperon-nucleon interaction, fss2, by using an inversion method based on supersymmetric quantum mechanics. Owing to the exact treatment of the Pauli-forbidden states between two $\alpha$ clusters, the present three-cluster Faddeev formalism can describe the mutually related, $\alpha \alpha$, $3\alpha$, and $\alpha \alpha \Lambda$ systems, in terms of a unique set of the baryon-baryon interactions. For the three-range Minnesota force which describes the $\alpha \alpha$ phase shifts quite accurately, the ground-state and excitation energies of ${}_{\Lambda }{}^9\mathrm{Be}$ are reproduced within $100–200\mathrm{keV}$ accuracy.

Low-momentum nucleon-nucleon interactions are derived within the framework of a unitary-transformation theory, starting with realistic nucleon-nucleon interactions. A cutoff momentum $\Lambda$ is introduced to specify a border between the low- and high-momentum spaces. By Faddeev-Yakubovsky calculations the low-momentum interactions are investigated with respect to the dependence of ground-state energies of ${}^3\mathrm{H}$ and ${}^4\mathrm{He}$ on the parameter $\Lambda$. It is found that we need the momentum cutoff parameter $\Lambda ⩾5{\mathrm{fm}}^{-1}$ in order to reproduce satisfactorily the exact values of the binding energies for ${}^3\mathrm{H}$ and ${}^4\mathrm{He}$. The calculation with $\Lambda =2{\mathrm{fm}}^{-1}$ recommended by Bogner et al. leads to considerable overbinding at least for few-nucleon systems.

High spin states in ${}^{237}\mathrm{Np}$ and ${}^{241}\mathrm{Am}$ have been studied with the “unsafe” Coulomb excitation technique. In each nucleus, signature partner rotational bands built on the $\left[523\right]5∕2^{-}$ and $\left[642\right]5∕2^{+}$ orbitals of respective $h_{9∕2}$ and $i_{13∕2}$ parentage have been delineated. An additional pair of bands based on the $\left[521\right]3∕2^{-}$ $\left(f_{7∕2}\right)$ state was also observed in ${}^{241}\mathrm{Am}$. New information on the even-even ${}^{236}\mathrm{Pu}$ and ${}^{242}\mathrm{Cm}$ transfer products is also presented. From the present data, the role of $i_{13∕2}$ protons in generating angular momentum in the even-even nuclei of the region is documented. A satisfactory description of the evolution of the rotational sequences with spin is achieved within the framework of the cranked shell model. Nevertheless, when combined with information on odd-neutron nuclei available from elsewhere, the data highlight significant shortcomings of the available theoretical predictions.

Ericson fluctuations in the differential cross sections were investigated for the compound reactions ${}^{27}\mathrm{Al}(p,n_0){}^{27}\mathrm{Si}$, ${}^{45}\mathrm{Sc}(p,n_4){}^{45}\mathrm{Ti}$, ${}^{45}\mathrm{Sc}(p,n_5){}^{45}\mathrm{Ti}$, ${}^{51}\mathrm{V}(p,n_0){}^{51}\mathrm{Cr}$, and ${}^{59}\mathrm{Co}(p,n_0){}^{59}\mathrm{Ni}$. Level widths in the compound nuclei ${}^{28}\mathrm{Si}$, ${}^{46}\mathrm{Ti}$, ${}^{52}\mathrm{Cr}$, and ${}^{60}\mathrm{Ni}$ were extracted from the analysis of the differential cross sections by the Fourier method and a nonlinear fit to the $\ln ⟨A_k^2+B_k^2⟩$ distribution. The neutron spectra for each reaction were measured at least at three backward angles but the coherence width $⟨\Gamma ⟩$ did not show a strong angular dependence. Nuclear level densities for the above nuclei were extracted by relating the average level spacing $D^{J\pi }$ to the average level width ${\Gamma }^{J\pi }$ using the fluctuation theory. Reasonable agreements were found with other level densities and level density compilations based in the Fermi gas formalism of Al-Quraishi and Huang for ${}^{28}\mathrm{Si}$, ${}^{46}\mathrm{Ti}$, and ${}^{52}\mathrm{Cr}$ but the comparison diverges for ${}^{60}\mathrm{Ni}$ for which additional measurements are required in order to clarify the observed discrepancies. The level density parameters that best describe the data are $a=3.5$ and $\delta =4.0$, $U<25\mathrm{MeV}$, for ${}^{28}\mathrm{Si}$, $a=4.8$ and $\delta =-0.3$, $U<20\mathrm{MeV}$, for ${}^{46}\mathrm{Ti}$, and $a=4.8$ and $\delta =0.3$, $U<20\mathrm{MeV}$, for ${}^{52}\mathrm{Cr}$.

Recently, there has been a significant amount of activity to try and understand the discrepancy between Rosenbluth and polarization transfer measurements of the proton form factors. It has been suggested that the standard use of plane-wave Born approximation in extracting the form factors is insufficient, and that higher-order terms must also be included. Of the corrections missing in standard prescriptions, Coulomb distortion is the most well understood. In this paper, we examine the effect of Coulomb distortion on the extraction of the proton form factors.

The nuclear spectral function at high missing energies and momenta has been determined from a self-consistent calculation of the Green’s function in nuclear matter using realistic nucleon-nucleon interactions. The results are compared with recent experimental data derived from $\left(e,e^{\prime }p\right)$ reactions on ${}^{12}\mathrm{C}$. A rather good agreement is obtained if the Green’s functions are calculated in a nonperturbative way.

Independent cross sections for all the $\mathrm{Hg}$ isotopes produced in the reaction of $600\text{−}\mathrm{MeV}$ ${}^{18}\mathrm{O}$ with a molten natural $\mathrm{Pb}$ target have been measured down to about $2\mu \mathrm{b}$. The measurement is based on a radiochemical gamma-spectroscopy technique combined with rapid gas thermochromatography. The observed $\mathrm{Hg}$-isotope distribution from ${}^{180}\mathrm{Hg}$ to ${}^{209}\mathrm{Hg}$ is compared with those previously reported from the reaction of $600\text{−}\mathrm{MeV}$ $p$ with a natural $\mathrm{Pb}$ target, and from two-proton-removal reactions measured by the inverse-kinematics method at relativistic energies. The comparisons make available some additional information for improving knowledge of spallation-reaction mechanisms in peripheral nuclear collisions. It is noted that the production cross sections for neutron-deficient heavy residues and the yield of fast neutrons emitted in proton-induced reactions should increase with increasing incident proton energy from $600\mathrm{MeV}$ to $1\mathrm{GeV}$.

We examine the two-pion interferometry for a granular source of quark-gluon plasma droplets. The evolution of the droplets is described by relativistic hydrodynamics with an equation of state suggested by lattice gauge results. Pions are assumed to be emitted thermally from the droplets at the freeze-out configuration characterized by a freeze-out temperature $T_f$. We find that the HBT radius $R_{\text{out}}$ decreases if the initial size of the droplets decreases. On the other hand, $R_{\text{side}}$ depends on the droplet spatial distribution and is relatively independent of the droplet size. It increases with an increase in the width of the spatial distribution and the collective-expansion velocity of the droplets. As a result, the value of $R_{\text{out}}$ can lie close to $R_{\text{side}}$ for a granular quark-gluon plasma source. The granular model of the emitting source may provide an explanation to the RHIC HBT puzzle and may lead to a new insight into the dynamics of the quark-gluon plasma phase transition.

We generalize the recoil polarization method for the determination of the proton form factor to the case of the disintegration of vector polarized deuterons by longitudinally polarized electrons, ${}^2\vec{\mathrm{H}}(\vec{e},e^{\prime }n)p$. We suggest measuring for this reaction, in the kinematics of quasielastic $en$ scattering, the ratio $R_{xz}=A_x∕A_z$ of the asymmetries induced by the $x$ and $z$ components of the deuteron vector polarization. Taking into account the final $np$ interaction through the experimental $np$ phase shifts, in the framework of the relativistic impulse approximation the ratio $R_{xz}$ is sensitive to $G_{En}$ in a wide interval of momentum-transfer squared, whereas it depends weakly on the details of the $np$ interaction and on the choice of the deuteron wave function. Moreover, in the range $0.5⩽Q^2⩽1.5{\mathrm{GeV}}^2$, the ratio $R_{xz}$ shows a smooth dependence on $Q^2$, making the analysis simpler.

Enrichment of the ${}^{100}\mathrm{Ru}$ isotope, resulting from the double beta $\left(\beta \beta \right)$ decay of ${}^{100}\mathrm{Mo}$, has been found in old molybdenites from Australia. Using $\mathrm{Re}–\mathrm{Os}$ ages determined here together with the amount of excess ${}^{100}\mathrm{Ru}$ determined via isotope dilution mass spectrometry, consistent half-lives were obtained from two different molybdenite samples of varying ages (2.90 billion and 1.05 billion years old) with an average half-life of $(2.1\pm 0.3)\times {10}^{18}$ years. This half-life is highly consistent with the theoretical model for a two-neutrino $\beta \beta$ decay.

We construct the density of states for quarks and gluons using the “Thomas-Fermi model” for atoms and the “Bethe model” for nucleons as templates. With parameters to take care of the plasma (hydrodynamical) features of the quark-gluon plasma (QGP) with a thermal potential for the interaction, we find a window in the parametric space of the model where observable QGP droplets of $\sim 5\mathrm{fm}$ radius can occur with transition temperature in the range $140–250\mathrm{MeV}$. By matching with the expectations of lattice gauge estimates of the QGP-hadron transitions, we can further narrow the window, thereby restricting the allowed values of the flow-parameters of the model.

We argue that although at asymptotically high temperatures the quark-gluon plasma (QGP) in bulk behaves as a gas of weakly interacting quasiparticles (modulo long-range magnetism), it is different at temperatures up to few times the critical temperature $T_c$. In particular, we emphasize the role of several zero binding lines on the phase diagrams, below which $\overline{c}c$, light quarks, $gg$ as well as exotic $gq,qq$ bound states exist. Near these lines quasiparticle rescattering is enhanced dramatically, possibly explaining why heavy-ion collisions at the relativistic heavy-ion collider exhibit robust collective phenomena. Although in QCD the coupling constant in the QGP phase reaches only values $g\sim 1$, using Maldacena duality one may study these phenomena in the strong coupling limit $g^2{N}_c⪡1$ in conformal gauge theories at finite temperature [e.g., $\mathcal{N}=4$ supersymmetric Yang-Mills (SUSY YM)]. Trapped atoms is another system which allows us to study strongly interacting matter, in the limit of infinite scattering length.