One-loop corrections to $\omega$ photoproduction near threshold have been investigated by using the approximation that all relevant transition amplitudes are calculated from the tree diagrams of effective Lagrangians. With the parameters constrained by the data of $\gamma \overrightarrow{N}\pi N,$ $\gamma \overrightarrow{N}\rho N,$ and $\pi \overrightarrow{N}\omega N$ reactions, it is found that the one-loop effects due to the intermediate $\pi N$ and $\rho N$ states can significantly change the differential cross sections and spin observables. The results from this exploratory investigation suggest strongly that the coupled-channel effects should be taken into account in extracting reliable resonance parameters from the data of vector meson photoproduction in the resonance region.

The Gari-Krümpelmann (GK) models of nucleon electromagnetic form factors, in which the $\rho ,$ $\omega ,$ and $\phi$ vector meson pole contributions evolve at high momentum transfer to conform to the predictions of perturbative QCD, was recently extended to include the width of the $\rho$ meson by substituting the result of dispersion relations for the pole and the addition of the ${\rho }^{\prime }$ (1450) isovector vector meson pole. This extended model was shown to produce a good overall fit to all the available nucleon electromagnetic form-factor data. Since then new polarization data shows that the electric to magnetic ratios $R_p$ and $R_n$ obtained are not consistent with the older $G_{\mathrm{Ep}}$ and $G_{\mathrm{En}}$ data in their range of momentum transfer. The model is further extended to include the ${\omega }^{\prime }$ (1419) isoscalar vector meson pole. It is found that while this GKex cannot simultaneously fit the new $R_p$ and the old $G_{\mathrm{En}}$ data, it can fit the new $R_p$ and $R_n$ well simultaneously. An excellent fit to all the remaining data is obtained when the inconsistent $G_{\mathrm{Ep}}$ and $G_{\mathrm{En}}$ is omitted. The model predictions are extended beyond the data, if needed, to momentum transfer squared, $Q^2,$ of $8{\mathrm{GeV}}^2{/c}^2.$

The effect on fission fragment anisotropies of the alignment of ground-state nuclear spin with the nuclear deformation axis has been investigated for the reactions ${}^{31}\mathrm{P}{+}^{176}\mathrm{Lu}$ and ${}^{29}\mathrm{Si}{+}^{178}\mathrm{Hf},$ through measurements at a range of energies spanning the fusion barrier. Calculations which reproduce the anisotropies for the ${}^{29}\mathrm{Si}{+}^{178}\mathrm{Hf}$ reaction only reproduce the anisotropies for ${}^{31}\mathrm{P}{+}^{176}\mathrm{Lu}$ when the correlation of the seven units of ground-state spin of ${}^{176}\mathrm{Lu}$ with the nuclear deformation axis is correctly taken into account.

The inclusive energy distributions of fragments $(3\mathrm{}<~Z<~7)$ emitted in the reaction ${}^{16}\mathrm{O}{+}^{27}\mathrm{Al}$ at $E_{\mathrm{lab}}=116\mathrm{}\mathrm{MeV}$ have been measured in the angular range ${\theta }_{\mathrm{lab}}=15\mathrm{}°–115°.$ A nonlinear optimization procedure using multiple Gaussian distribution functions has been proposed to extract the fusion-fission and deep-inelastic components of the fragment emission from the experimental data. The angular distributions of the fragments, thus obtained, from the deep-inelastic component are found to fall off faster than those from the fusion-fission component, indicating shorter lifetimes of the emitting dinuclear systems. The lifetimes of the intermediate dinuclear configurations have been estimated using a diffractive Regge-pole model. The lifetimes thus extracted $\left[\sim \right(1\mathrm{}–5)\times {10}^{-22}\sec ]$ are found to decrease with the increase in the fragment charge. Optimum Q values are also found to increase with increasing charge transfer, i.e., with the decrease in fragment charge.

Self-affine multiplicity scaling is investigated in the framework of a two-dimensional factorial moment methodology using the concept of the Hurst exponent (H). Our investigation on experimental data of the medium energy target protons (gray particles) emitted in ${}^{32}\mathrm{S}-\mathrm{A}\mathrm{g}\mathrm{B}\mathrm{r}$ interactions at 200A GeV and ${}^{16}\mathrm{O}-\mathrm{A}\mathrm{g}\mathrm{B}\mathrm{r}$ interactions at 60A GeV reveals that a better power-law behavior is exhibited in self-affine analysis at $H=0.4\mathrm{}$ in both type of interactions. This work reports the first ever evidence of self-affine behavior of knocked out target protons.

This paper investigates how the breaking of manifest rotational invariance in light-front dynamics affects the binding energy and the form factors of the deuteron. To do this, we derive new light-front nucleon-nucleon one- and two-meson-exchange potentials, and use the potentials to solve for the deuteron wave function and binding energy. We find that including two-meson-exchange (TME) potentials partially repairs the broken rotational invariance of the one-meson-exchange (OME) potential. This is shown by a decrease in the binding energy difference of different m states of the deuteron. We calculate the matrix elements of the electromagnetic current using the deuteron wave functions obtained from the OME and $\mathrm{OME}+\mathrm{TME}$ potentials. Rotational invariance requires that the matrix elements satisfy an angular condition, but in light-front dynamics that condition is only partially satisfied. The current matrix elements from the OME calculation satisfy the angular condition better than the ones from the $\mathrm{OME}+\mathrm{TME}$ calculation. The matrix elements of the axial current satisfy the angular condition to the same extent regardless of which wave functions are used for the calculation. Finally, we find that at momentum transfers greater than about $2{\mathrm{GeV}}^2,$ the breaking of rotational invariance causes less uncertainty in the computed deuteron form factors than do the uncertainties in the nucleon form factors.

A complete set of $\pi d$ polarization observables, including polarization transfer, in $\pi d$ elastic scattering have been measured at backwards scattering angles for two pion energies below and at the $\Delta \mathrm{}(3,3)\mathrm{}$ resonance. Our results for the analyzing powers are in good agreement with the existing world dataset, while polarization transfer observables have not been measured before. The experimental data are compared to relativistic Faddeev calculations and different Virginia Tech Partial-Wave Analysis Facility solutions, in the laboratory as well as in the center-of-mass system.

The ${}^{99}\mathrm{Ru}{\mathrm{}(d,t)\mathrm{}}^{98}\mathrm{Ru}$ reaction was measured for the first time at 16 MeV incident energy with the São Paulo Pelletron-Enge-spectrograph facility employing the nuclear emulsion technique. In all, up to 3.5 MeV, 23 levels were detected, eight of them new; angular distributions are presented for all of them. Least squares fits of distorted wave Born approximation one-neutron pickup predictions to the rather well structured experimental angular distributions enabled the determination of l transfers and of the corresponding spectroscopic factors for 19 of these states, some being tentative attributions. Only transfers of $l=0,$ 2, and 4 were observed. Several states were populated through single l transfers. A pure $l=2\mathrm{}$ transfer is associated with the $2_1^{+}$ level and with several other states which are considered collective, as well as with the ${(4\mathrm{}}^{+})$ state at 2.277 MeV, which presents the highest spectroscopic strength. Considering five valence neutrons above the $N=50\mathrm{}$ core, only 41% of the spectroscopic strength expected for ${}^{99}\mathrm{Ru}$ was detected.

It is shown that under changing density or temperature a nucleon Fermi superfluid can undergo a phase transition to an anisotropic superfluid state, characterized by nonvanishing gaps in pairing channels with singlet-singlet (SS) and triplet-singlet (TS) pairing of nucleons (in spin and isospin spaces). In the SS pairing channel nucleons are paired with nonzero orbital angular momentum. Such two-gap states can arise as a result of branching from the one-gap solution of the self-consistent equations, describing SS or TS pairing of nucleons, that depends on the relationship between SS and TS coupling constants at the branching point. The density/temperature dependence of the order parameters and the critical temperature for transition to the anisotropic two-gap state are determined in a model with the SkP effective interaction. It is shown that the anisotropic SS-TS superfluid phase corresponds to a metastable state in nuclear matter.

The dynamical symmetry X(5) characterizes the critical point of phase transition between spherical and axially deformed shape in atomic nuclei. A first example of this new symmetry has been found in ${}^{152}\mathrm{Sm}$ $\mathrm{}(Z=62\mathrm{})\mathrm{}$ by Casten and Zamfir. We show that the level scheme of the transitional nucleus ${}^{104}\mathrm{Mo}$ $\mathrm{}(N=62\mathrm{})\mathrm{}$ also presents the characteristic X(5) pattern, not only in the ground-state band but also in its low-lying $n_{\gamma }=1,K=2\mathrm{}$ and $n_{\gamma }=2,K=4\mathrm{}$ bands. An essential point of the model leading to the X(5) symmetry, i.e., the decoupling of the $\gamma$ vibrations from the other degrees of freedom, is therefore confirmed.

Nuclear caloric curves have been analyzed using an expanding Fermi gas hypothesis to extract average nuclear densities. In this approach the observed flattening of the caloric curves reflects progressively increasing expansion with increasing excitation energy. This expansion results in a corresponding decrease in the density and Fermi energy of the excited system. For nuclei of medium to heavy mass apparent densities $\sim 0.4{\rho }_0$ are reached at the higher excitation energies.

We search for approximate, but analytic, solutions of the pairing problem for one pair of nucleons in many levels of a potential well. For the collective energy a general formula, independent of the details of the single particle spectrum, is given in both the strong and weak coupling regimes. Next the displacements of the solutions trapped in between the single particle levels with respect to the unperturbed energies are explored: their dependence upon a suitably defined quantum number is found to undergo a transition between two different regimes.

We investigated ${}^{108}\mathrm{Cd}$ using a powerful combination of complementary γγ spectroscopic methods. Excited states were populated in the β decay of ${}^{108}\mathrm{In}$ and with the ${}^{105}\mathrm{Pd}(\alpha ,n)$ fusion-evaporation reaction near the Coulomb barrier. From γγ angular correlation analyses we found dominant $M1\mathrm{}$ character for decays of three $2^{+}$ states between 2.1 and 2.65 MeV, indicating that the fundamental isovector quadrupole excitation in the valence shell, the so-called $2_{\mathrm{ms}}^{+}$ state, is fragmented in ${}^{108}\mathrm{Cd}.$ Effective lifetimes from the Doppler-shift attenuation method (DSAM) provided lower limits for the absolute transition strengths of the interesting decays. Our findings on mixed-symmetry $2^{+}$ states were compared to the neighboring nucleus ${}^{112}\mathrm{Cd}$ and IBM-2 predictions in the vicinity of the pure U(5) and O(6) dynamical symmetry limits. Furthermore, indications for the $1_{\mathrm{ms}}^{+}$ excitation of ${}^{108}\mathrm{Cd}$ were found. In total we established more than 120 new states and more than 580 new transitions, 30 spins and 80 multipole mixing ratios were determined and eight effective lifetimes stem from DSAM. This huge amount of new data enabled an investigation of the excitation spectrum even under statistical aspects. We discuss the frequency of spin values below 3.13 MeV in the framework of the constant temperature model.

Deformation is fundamental to understanding nuclear structure. We compare two ways to efficiently realize deformation for many-fermion wave functions, the leading SU(3) irreducible representation and the angular-momentum-projected Hartree-Fock state. In the absence of single-particle spin-orbit splitting the two are nearly identical. With realistic forces, however, the difference between the two is nontrivial, with the angular-momentum-projected Hartree-Fock state better approximating an “exact” wave function calculated in the fully interacting shell model. The difference is driven almost entirely by the single-particle spin-orbit splitting.

One-body overlap functions play an important role for the description of nuclear structure and nuclear reactions. Equations of motion for the one-body overlaps, based on particle-only, hole-only, and particle-hole approaches, are studied. A given overlap function is shown to satisfy four different Schrödinger-like equations, all of which can be derived in the framework of the Feshbach projection operator formalism. Approximating the relevant potential by a local potential is only valid in the particle-hole approach. Previously proposed one-body functions, which can be derived from the overlap functions, are also considered. It is argued that the latter do not satisfy a Schrödinger-like equation with an approximately local potential.

Pion virtual compton scattering (VCS) via the reaction ${\pi }^{-}\overrightarrow{e}{\pi }^{-}e\gamma$ was observed in the Fermilab E781 SELEX experiment. SELEX used a $600\mathrm{GeV}/c$ ${\pi }^{-}$ beam incident on target atomic electrons, detecting the incident ${\pi }^{-}$ and the final state ${\pi }^{-},$ electron and $\gamma .$ Theoretical predictions based on chiral perturbation theory are incorporated into a Monte Carlo simulation of the experiment and are compared to the data. The number of reconstructed events (=9) and their distribution with respect to the kinematic variables (for the kinematic region studied) are in reasonable accord with the predictions. The corresponding ${\pi }^{-}$ VCS experimental cross section is σ=38.8±13 nb, in agreement with the theoretical expectation of σ=34.7 nb.

We present measurements of the recoil proton polarization for the ${}^{1}H(\overrightarrow{\gamma },\overrightarrow{p}){\pi }^0$ reaction for ${\theta }_{\mathrm{c}.\mathrm{m}.\mathrm{}}^{\pi }=60\mathrm{}°–135°$ and for photon energies up to 4.1 GeV. These are the first data in this reaction for polarization transfer with circularly polarized photons. Various theoretical models are compared with the results. No evidence for hadron helicity conservation is observed. Models that employ factorization are not favored. It appears from the strong angular dependence of the induced polarization at photon energies of 2.5 and 3.1 GeV that a relatively high spin resonance or background amplitude might exist in this energy region.

We calculate the cross-section for the excitation and subsequent decay of triple giant resonances (TGR’s) in several nuclei excited with heavy ions. The recently developed coherent plus incoherent theory for the excitation in conjunction with the hybrid decay model of Dias, Hussein, and Adhikari are used for the purpose. It is emphasized that the direct decay of the TGR is expected to deviate appreciably from the harmonic limit especially at low bombarding energies, owing to the incoherent contribution.

We perform a field-theoretical computation of hadron production in large systems at the QCD confinement phase transition associated with restoration of the $Z\left(3\right)\mathrm{}$ global symmetry. This occurs from the decay of a condensate for the Polyakov loop. From the effective potential for the Polyakov loop, its mass just below the confinement temperature $T_c$ is in between the vacuum masses of the pion and that of the kaon. Therefore, due to phase-space restrictions the number of produced kaons is roughly an order of magnitude smaller than that of produced pions, in agreement with recent results from collisions of gold ions at the BNL-RHIC. From its mass, we estimate that the Polyakov loop condensate is characterized by a (spatial) correlation scale of ${1/m}_l\simeq 1/2\mathrm{fm}.$ For systems of deconfined matter of about that size, the free energy may not be dominated by a condensate for the Polyakov loop, and so the process of hadronization may be qualitatively different as compared to large systems. In that vein, experimental data on hadron abundance ratios, for example $K/\pi ,$ in high-multiplicity $\mathrm{pp}$ events at high energies should be very interesting.