A relativistic model for the quasifree photoproduction of $\eta$ mesons from complex nuclei is developed. The interactions between fields are introduced through effective Lagrangians. Contributions from several nucleon resonances as well as nucleon Born terms and vector meson exchange diagrams are included. Nucleon and $\eta$ wave functions are solutions of Dirac and Klein-Gordon equations, respectively. Final state interactions of the outgoing particles are included via optical potentials. The effects of these interactions on the cross sections and photon asymmetries are studied and are found to be large. Calculations indicate that at energies near threshold the exclusive reaction takes place mainly through formation of the $S_{11}$(1535) resonance. Comparisons with the nonrelativistic calculations show differences between the two approaches both for the cross sections and photon asymmetries. We give some detailed predictions for the reaction observables for exclusive photoproduction on ${}^{12}$C, ${}^{16}$O, and ${}^{40}$Ca.

An investigation of the transition to $\Delta$ matter is performed based on a relativistic mean field formulation of the nonlinear $\sigma$ and $\omega$ model. We demonstrate that in addition to the $\Delta$-meson coupling, the occurrence of the baryon resonance isomer also depends on the nucleon-meson coupling. Our results show that for the favored phenomenological value of $m^{*}$ and $K$, the $\Delta$ isomer exists at baryon density $\sim 2$–3${\rho }_0$ if $\beta$=1.31 is adopted. For universal coupling of the nucleon and $\Delta$, the $\Delta$ density at baryon density $\sim 2$–3${\rho }_0$ and temperature $\sim 0.4$–0.5 fm${}^{-1}$ is about normal nuclear matter density, which is in accord with a recent experimental finding.

The effect of narrow dibaryon resonances on basic nuclear matter properties and on the structure of neutron stars is investigated in mean-field theory and in relativistic Hartree approximation. The existence of massive neutron stars imposes constraints on the coupling constants of the ω and σ mesons with dibaryons. In the allowed region of the parameter space of the coupling constants, a Bose condensate of the light dibaryon candidates $d_1\mathrm{}\left(1920\right)\mathrm{}$ and $d^{\prime }\mathrm{}\left(2060\right)\mathrm{}$ is stable against compression. This proves the stability of the ground state of heterophase nuclear matter with a Bose condensate of light dibaryons.

The $\Delta$ decay in the nuclear medium is calculated in the relativistic meson-nucleon model. The $\Delta$ spreading width is calculated and compared with the Pauli-blocked $\pi N$ decay width. The influence of relativistic mean fields is also studied. We stress the importance of understanding the $\Delta$ spreading width in interpreting experiments involving $\Delta$ resonances.

We revisit the QCD sum-rule treatment of the isospin-breaking correlator $〈{0\left|T\right[A}_{\mu }^3{\mathrm{}\left(x\right)A}_{\nu }^8\mathrm{}\left(0\right)\left]\right|0\mathrm{}〉$, in light of the recent claim that a previous treatment produced results incompatible with known chiral constraints. The source of the error in the previous analysis is identified, and a corrected version of the sum-rule treatment obtained. It is then shown that, using input from chiral perturbation theory, one may use the resulting sum rule to extract information on the leading chiral behavior of isospin-breaking parameters associated with the coupling of excited pseudoscalar resonances to the axial currents. A rather accurate extraction is possible for the case of the ${\eta }^{\prime }$. Demanding stability of the sum-rule analysis also allows us to improve the upper bound on the fourth-order low-energy constant, $L_7$.

A suitable numerical approach based on Sturmian functions is employed to solve the $\overline{N}N$ bound state problem for local and nonlocal potentials. The approach accounts for both the strong short-range nuclear potential and the long-range Coulomb force and provides directly the wave function of protonium and $\overline{N}N$ deep bound states with complex eigenvalues ${E=E}_R-i(\Gamma /2)$. The spectrum of $\overline{N}N$ bound states has two parts, the atomic states bound by several keV, and the deep bound states which are bound by several hundred MeV. The observed very small hyperfine splitting of the $1s$ level and the $1s$ and $2p$ decay widths are reasonably well reproduced by both the Paris and Bonn potentials (supplemented with a microscopically derived quark annihilation potential), although there are differences in magnitude and level ordering. We present further arguments for the identification of the ${}^{13}{\mathrm{PF}}_2$ deep bound state with the exotic tensor meson $f_2\mathrm{}\left(1520\right)\mathrm{}$. Both investigated models can accommodate the $f_2\mathrm{}\left(1520\right)\mathrm{}$ but differ greatly in the total number of levels and in their ordering. The model based on the Paris potential predicts the ${}^{13}{P}_0$ level slightly below 1.1 GeV while the model based on the Bonn potential puts this state below 0.8 GeV. It remains to be seen if this state can be identified with a scalar partner of the $f_2\mathrm{}\left(1520\right)\mathrm{}$.

The ${}^7\mathrm{Li}(p\to ,\gamma {)}^8\mathrm{Be}$ reaction has been studied in the laboratory energy range $E_p=80\mathrm{}$–0 keV. The vector analyzing powers $A_y\left(\theta \right)$ and the angular distributions of the cross section $d\sigma /d\Omega \left(\theta \right)$ for capture to the ground, first-, and third-excited states are reported. Additionally, the absolute cross section ${\sigma }_T\mathrm{}\left(E\right)\mathrm{}$ and (equivalently) the astrophysical $S$ factor $S\left(E\right)\mathrm{}$ have been measured for capture to the third-excited state. Calculations have been performed for all three transitions using the direct capture model to which the known nearby $M$1 resonances were added. While they predict the angular distribution observed for the cross section and analyzing power in the case of both the first and third-excited states of ${}^8$Be, they do not reproduce those for the ground state. These calculations predict negligible $M$1 strength below 80 keV for capture to the third-excited state ${(2\mathrm{}}^{+}$, $T=0+1\mathrm{}$, 16.6 MeV), and we therefore conclude that the extrapolation of the astrophysical $S$ factor for the ${}^7\mathrm{Be}(p,\gamma {)}^8\mathrm{B}$ reaction, which has been performed previously by assuming pure $E$1 capture, is valid with regard to the neglect of any significant $p$-wave capture strength.

The prediction of cross sections for nuclei far off stability is crucial in the field of nuclear astrophysics. In recent calculations the nuclear level density—as an important ingredient to the statistical model (Hauser-Feshbach)—has shown the highest uncertainties. We present a global parametrization of nuclear level densities within the back-shifted Fermi-gas formalism. Employment of an energy-dependent level density parameter $a$, based on microscopic corrections from a recent finite range droplet model mass formula, and a backshift $\delta$, based on pairing and shell corrections, leads to a highly improved fit of level densities at the neutron-separation energy in the mass range $20<~A<~245$. The importance of using proper microscopic corrections from mass formulas is emphasized. The resulting level description is well suited for astrophysical applications. The level density can also provide clues to the applicability of the statistical model which is only correct for a high density of excited states. Using the above description, one can derive a “map” for the applicability of the model to reactions of stable and unstable nuclei with neutral and charged particles.

${}^{224}\mathrm{Pa}$ was produced via the ${}^{209}{\mathrm{B}\mathrm{i}(}^{18}\mathrm{O},3n)$ reaction at the Lawrence Berkeley National Laboratory 88-Inch Cyclotron and the half-life was determined to be 850±20 ms by measuring its alpha decay using our rotating wheel system. Our value is consistent with a previously reported half-life of 950±150 ms for ${}^{224}\mathrm{Pa}$ produced via the ${}^{205}{\mathrm{T}\mathrm{l}(}^{22}\mathrm{N}\mathrm{e},3n)$ reaction, but its much more precise. The cross section for the ${}^{209}{\mathrm{B}\mathrm{i}(}^{18}\mathrm{O},{3n)}^{224}\mathrm{Pa}$ reaction was measured to be 0.5±0.1 mb for 87–89 MeV ${}^{18}{\mathrm{O}}^{5+}$ projectiles incident on the target.

High-spin states in the nucleus ${}^{123}$I were populated by the ${}^{110}$Pd${(}^{16}$O,$p4n)$ reaction at 75 MeV. $\gamma$-ray energies, intensities, $\gamma$-$\gamma$ coincidences, and directional correlation ratios were measured. The rotational band built on the $\pi h_{11/2}$ single-particle state was extended to spin ${I=35/2\mathrm{}}^{-}$; at higher spin the level spacings and the feeding pattern were found to become irregular, indicating a sudden change of structure. The 39/2${}^{-}$ state and a higher-lying ${43/2}^{-}$ level were interpreted as aligned oblate states, in line with the systematics of the lighter odd-$A$ iodine isotopes. Total Routhian surface calculations were performed and were found to support the occurrence of a band termination. Higher-lying levels that feed the $h_{11/2}$ band were identified, reaching spin $I>~47/2$ and an excitation energy of about 9 MeV.

The effective $\mathrm{NN}$-interaction strength for the first $\mathrm{NN}$ collision in multistep reactions, averaged along the trajectory of the incident nucleon with respect to both the nuclear density and the first $\mathrm{NN}$-collision probability, is obtained. Good agreement between the calculated values of this quantity and its phenomenological values is found. The account for the finite-range corrections to the involved local density approximation has a small effect on the average strength of the $\mathrm{NN}$ interaction. It is concluded that the nuclear-density dependence of the effective $\mathrm{NN}$ interaction may account for the phenomenological $V_0$ values which have been underestimated at low energies when the trend of the optical-model potential only has been followed.

We calculate the dilepton emissions as the decay product of the charm and bottom quarks produced in heavy-ion collisions at RHIC energy. We take into account the next-to-leading-order radiative corrections in perturbative QCD to the heavy quark production from an initial hard parton-parton scattering. We find that the thermal charm decay dominates the dilepton production in the low dilepton mass region $(<\mathrm{}2\mathrm{}$ GeV), while the heavy quark production from the initial scattering takes over the intermediate and high mass regions $(>\mathrm{}2\mathrm{}$ GeV). Our result also indicates the importance of the bottom quark in the high mass region $(>\mathrm{}4\mathrm{}$ GeV) due to its large mass and cascade decay. If the initial scattering produced charm suffers a significant energy loss due to the secondary interaction, the bottom decay constitutes the major background for the thermal dileptons.

From the recent measurement of parity nonconservation (PNC) in the Cs atom we have extracted the constant of the nuclear spin dependent electron-nucleon PNC interaction, $\kappa =0.442\mathrm{}\left(63\right)\mathrm{}$; the anapole moment constant, ${\kappa }_a=0.364\mathrm{}\left(62\right)\mathrm{}$; the strength of the PNC proton-nucleus potential, $g_p=7.3\mathrm{}\pm 1.2\left(\mathrm{expt}\right)\pm 1.5\left(\mathrm{theor}\right)$; the $\pi$-meson-nucleon interaction constant, $f_{\pi }\equiv h_{\pi }^1=[9.5\mathrm{}\pm 2.1(\mathrm{expt})\pm 3.5(\mathrm{theor}\left)\right]\times {10}^{-7}$; and the strength of the neutron-nucleus potential, $g_n=-1.7\pm 0.8\left(\mathrm{expt}\right)\pm 1.3\left(\mathrm{theor}\right)$.

We question the reliability of current estimates for the ${\Delta }^{+}$ mass. We explain why the standard value, determined from pion photoproduction, should not be used in conjunction with present estimates for the ${\Delta }^{++}$ and ${\Delta }^0$ masses, determined from pion-nucleon scattering. The resultant mass splittings are internally inconsistent. We also briefly comment on discrepancies found when “theoretical” and “experimental” values for the $\Delta$ masses are compared.

The ${}^{14}\mathrm{O}(\alpha {,p)}^{17}$F and ${}^{17}\mathrm{F}(p,\gamma {)}^{18}$Ne astrophysical reaction rates are needed to determine the breakout conditions from the hot CNO cycle into the rapid proton capture process in hot stellar environments. We have examined recent indirect experimental measurements of these reactions and generated analytical expressions for the reaction rates as a function of temperature. We also present a correction to the previously reported calculation of the ${}^{17}\mathrm{F}(p,\gamma )$ rate.

The dependence of the intermediate-mass-fragment (IMF) charge distribution on the multiplicity $N_{\mathrm{IMF}}$ of detected fragments has been investigated in projectile fragmentation ALADIN data from $E/A$ = 600, 800, and 1000 MeV ${}^{197}$Au + ${}^{197}$Au collisions. The observed dependence can be parametrized as $P_{N_{\mathrm{IMF}}}\mathrm{}\left(Z\right)\mathrm{}\propto \tilde{P}\mathrm{}\left(Z\right)\mathrm{}\exp \left(-{\mathrm{cN}}_{\mathrm{IMF}}Z\right)$ where $c$ is an excitation-energy-dependent parameter whose value evolves from near zero to a positive quantity as a function of $Z_{\mathrm{bound}}.$

A search for the double-γ vibration is performed using thermal neutron capture on ${}^{163}\mathrm{Dy}.$ A level at 2173 keV in ${}^{164}\mathrm{Dy}$ is found to exhibit a collective enhancement in its decay to the single-γ vibration, suggesting a contribution from the $K^{\pi }{=4\mathrm{}}^{+}$ double-γ excitation. Both its energy and the measured $B\left(E2\mathrm{}\right)\mathrm{}$ value to the single-γ vibration are in reasonable agreement with the different theoretical predictions.

A 39$A$ MeV ${}^{38}\mathrm{S}$ radioactive beam was used with inverse kinematics to measure angular distributions for elastic and inelastic proton scattering from a ${\mathrm{CH}}_2$ target. Optical potential and folding model calculations are compared with the elastic distribution. Using coupled channel calculations, the ${\beta }_2$ value for the $2_1^{+}$ state is determined to be 0.35±0.04. This value, when compared with the corresponding result from a Coulomb excitation measurement, leads to $M_n{/M}_p$=(1.5±0.3)$N/Z,$ indicating an isovector contribution to the $2_1^{+}$ state of ${}^{38}\mathrm{S}.$