Charge-independence breaking due to the pion-mass difference in the (chiral) two-pion-exchange nucleon-nucleon force is investigated. A general argument based on symmetries is presented that relates the charge-symmetric part of that force to the proton-proton case. The static potential linear in that mass difference is worked out as an explicit example by means of Feynman diagrams, and this confirms the general argument.

We study the spectrum of the bremsstrahlung photons coming from the electrons and positrons, which are produced in the strong electromagnetic fields present in peripheral relativistic heavy-ion collisions. We compare different approaches, making use of the exact pair production cross section in heavy-ion collisions as well as the double equivalent photon approximation.

Using a relativistic transport model, we study the azimuthal momentum asymmetry of kaons with fixed transverse momentum, i.e., the differential flow, in heavy-ion collisions at beam momentum of $6\hspace{0.5em}\mathrm{GeV}/c$ per nucleon, available from the Alternating Gradient Synchrotron (AGS) at the Brookhaven National Laboratory (BNL). We find that in the absence of kaon potential the kaon differential flow is positive and increases with transverse momentum as that of nucleons. The repulsive kaon potential as predicted by theoretical models, however, reduces the kaon differential flow, changing it to negative for kaons with low transverse momenta. Cancellation between the negative differential flow at low momenta and the positive one at high momenta is then responsible for the experimentally observed nearly vanishing in-plane transverse flow of kaons in heavy-ion experiments.

Identical particle correlations at fixed multiplicity are considered in the presence of chaotic and coherent fields. The multiplicity distribution, one-particle momentum density, and two-particle correlation function are obtained based on the diagrammatic representation for cumulants in semi-inclusive events. Our formulation is applied to the analysis of the experimental data on the multiplicity dependence of correlation functions reported by the UA1 and the OPAL Collaborations.

We improved the accuracy of calculating the exchange α-nucleus real potential by suggesting a simple expression for the nondiagonal density matrix of α-particle $\{{\rho }_{\alpha }(\overrightarrow{r},r^{\prime })\}.$ We found that this expression reduces the error in calculating the total α-nucleus potential by more than 20% compared with using the density matrix expansion method to treat ${\rho }_{\alpha }(\overrightarrow{r},r^{\prime }).\mathrm{}$

The $d^{*}\to d\pi \pi$ partial decay width has been calculated in a wave-function model for $d^{*}$ and d. It is found to be smaller than a previous estimate by a factor of 7. A previously proposed dependence on dibaryon sizes is confirmed. The large reduction found is caused partly by a change in the $d^{*}$ size used and partly by the need to match momenta in pion emissions, a feature not included in the previous estimate.

The criteria suggested by Welsh and Fearing to judge the validity of certain soft-photon amplitudes are examined. Some aspects of their analysis lead to incorrect conclusions.

We respond to the preceding Comment on our paper, “Validity of certain soft photon amplitudes.” While we hope the discussion here clarifies the issues, we have found nothing which leads to a change in the original conclusions of our paper.

Using a harmonic oscillator model, it is shown that the isovector giant quadrupole resonance carries little isoscalar quadrupole strength while the isoscalar giant quadrupole resonance contains an isovector strength with $B\left(\mathrm{IV}\right)/B\left(\mathrm{IS}\right)\mathrm{}\approx \left(\mathrm{}\right(N-Z)/A{)}^2,$ when a consistency condition is fulfilled. Taking into account the consistency between the one-particle excitation spectra and the vibrational fields is of vital importance in the proper estimate of the ratio of the contribution by neutrons to that by protons to collective excitations of nuclei with $N\ne Z.\mathrm{}$ The ratio may not be properly estimated in the models such as traditional shell models, in which the Coulomb potential (or interaction) is simulated by using the parameters ${\omega }_p<{\omega }_n$ for nuclei with a neutron excess.

A gas proportional chamber has been employed to make precise observations of the low-energy portion of the ${}^3\mathrm{H}$ β spectrum in methane molecules. This spectrum has been well fit to the combination of an electron screening potential of $76\pm 4$ (stat) $\pm 9$ (sys) eV, simultaneously with $-22\pm 3$ (stat) $\pm 9$ (sys) eV of molecular neutralization energy recovered in ionization of the gas. Both of these values are consistent with expectations based on self-consistent field predictions.

The coupled $\pi N,$ $\eta N,$ $\gamma N$ systems are described by a K-matrix method. The parameters in this model are adjusted to get an optimal fit to $\pi \overrightarrow{N}\pi N,$ $\pi \overrightarrow{N}\eta N,$ $\gamma \overrightarrow{N}\pi N$, and $\gamma \overrightarrow{N}\eta N$ data in an energy range of about 100 MeV each side of the $\eta$ threshold. The coupling of photons to the $N\left(1535\right)\mathrm{}$ state is extracted and also an alternative to the current $S11\mathrm{}\gamma \overrightarrow{N}\pi N$ amplitudes suggested. Expansions are given for the $\eta \eta$ and $\gamma \eta$ amplitudes in terms of the $\eta$ momentum. Effects of interference of this state with background potential interactions are discussed and experimental consequences are indicated.

By studying the disassembly of excited drops within the framework of the classical molecular dynamics (CMD) model, a critical review of observables which can give a signature of a critical behavior is performed. In particular we look at the normalized variance of the mass of the largest fragment (NVM) and to the intermittency signal (IS). It is found the NVM displays a maximum in the critical region for CMD and percolation models, while it is not triggered in “noncritical” data like the one resulting from the random partition model. On the other hand, the IS displays a maximum when events with a big fragment are mixed with events composed mainly of small clusters.

General formulas of analyzing powers in nuclear reactions are derived in a model-independent way, decomposing the analyzing powers by the rank of tensors in the spin space by the invariant-amplitude method. The validity of the formulas is examined in low energy reactions, the ${}^3\mathrm{He}(\overrightarrow{d}{,p)}^4\mathrm{He}$ reaction at the 430-keV resonance and ${}^1\mathrm{H}(\overrightarrow{d},\gamma {)}^3\mathrm{He}$ reactions at energies below 80 keV, for which the formulas reproduce experimental data very well. The analyses clarify the following. The former reaction occurs mainly due to tensor interactions with incident $S$ waves while $P$ wave corrections by spin-orbit interactions have indispensable contributions to the analyzing powers. The data of the latter reaction are explained by the vector transition amplitudes in the spin space. The formulas predict the angular distribution of the analyzing power $T_{\mathrm{kq}}$ $(k=\mathrm{even})$ to be similar to $P_k^q\left(\cos \theta \right)$ for incident $S$ waves when $Q$ values are finite.

We study the pionic decay of a possible dibaryon $d^{\prime }\to \pi +NN$ and pion decay of single baryons. The ${}^3{P}_0$ quark-pair-creation model is used for the definition of the effective quark-pion coupling. All necessary coupling constants and vertex form factors both in the baryonic and dibaryonic sectors are calculated in this model using translationally invariant quark-shell-model configurations. A hypothesis for the mass shift of the $d^{\prime }$ in a nuclear medium is discussed in order to explain the position of the resonance peak observed in double-charge exchange reactions in nuclei and the nonobservation (or at least doubtful observations) of the $d^{\prime }$ as a free resonance outside of a nuclear medium. In this connection the dependence of the $d^{\prime }$ decay width on the $d^{\prime }$ mass is calculated for two alternative models of the final-state $\mathrm{NN}$ interaction (one-boson exchange potential and Moscow potential). Off-shell effects in the $d^{\prime }$ decay are studied on the basis of an algebraic quark-cluster model technique.

Various quasipotential two-body scattering equations are studied at the one-loop level for the case of both t- and u-channel exchange potentials. We find that the quasipotential equations devised to satisfy the one-body limit for the t-channel exchange potential can be in large disagreement with the field-theoretical prediction in the case of u-channel exchange interactions. Within the spectator model, the description of the u-channel case improves if another choice of the spectator particle is made. Since the appropriate choice of the spectator depends strongly on the type of interaction used, one faces a problem when both types of interaction are contained in the potential. Equal-time formulations are presented, which, in the light-heavy particle system corresponding to the mass situation of the $\pi N$ system, approximate in a reasonable way the field-theoretical result for both types of interactions.

Manifestations of pronounced shell effects are found when combining nonaxial octupole deformations with a three-dimensional harmonic oscillator model. The contributions of the main classical periodic orbits of this intrinsically chaotic three degrees of freedom system are obtained from a frequency analysis. An adiabatic approximation based on the removal of resonance method yields explicit expressions for winding numbers from which the quantum spectrum can be predicted. The shell structure obtained from this quadrupole+octupole combination turns out to be equivalent to the shell structure of a plain but more strongly deformed quadrupole potential for about the first 100 levels.

We report calculations for exclusive pion photoproduction on nuclei beyond the first resonance region in the distorted wave impulse approximation. The elementary operator contains contributions from the resonances $P_{33}\mathrm{}\left(1232\right),$ $P_{11}\mathrm{}\left(1440\right),$ $D_{13}\mathrm{}\left(1520\right),$ $D_{33}\mathrm{}\left(1700\right),$ $S_{11}\mathrm{}\left(1535\right),$ $S_{11}\mathrm{}\left(1650\right),$ and $F_{15}\mathrm{}\left(1680\right),$ in addition to the usual Born plus vector meson contributions. It gives a good description of single pion photoproduction data up to about 1.1 GeV. Final state interactions are incorporated via optical potentials and are found to be substantial in the coincidence cross sections, but insensitive to the photon asymmetry. Clear signatures of possible medium modifications of the $D_{13}$ and $F_{15}$ resonances are predicted under selected kinematics.

It is shown that the true parameters of ${}_{\Sigma }^4\mathrm{He}$ differ from the observed ones. The reason is that the amplitude of ${}_{\Sigma }^4\mathrm{He}$ production in the reaction ${}^4\mathrm{He}{(K}^{-},{\pi }^{-})$ sharply varies just in the corresponding mass region. This leads to a small, but noticeable shift of the binding energy and the width. In addition, the data at the threshold of ${\Sigma }^0$ production is found to give additional evidence that the ${}_{\Sigma }^4\mathrm{He}$ width cannot exceed $8.5–9.0\hspace{0.5em}\mathrm{MeV}.$

The ${B(E2;0\mathrm{}}_{\mathrm{g}.\mathrm{s}.\mathrm{}}^{+}\to 2_1^{+})$ value for ${}^{38}\mathrm{Ca}$ has been measured via the technique of intermediate energy Coulomb excitation using a beam of radioactive ${}^{38}\mathrm{Ca}$ nuclei. The present result is used to test isospin purity in the mass 38 system by comparing the isoscalar multipole matrix element $M_0$ extracted from the $0_{\mathrm{g}.\mathrm{s}.\mathrm{}}^{+}\to 2_1^{+}$ transitions in ${}^{38}\mathrm{Ca}$ and ${}^{38}\mathrm{Ar}$ to the corresponding matrix element obtained from the $T=1\mathrm{}$ states of the $T_z=0\mathrm{}$ nucleus ${}^{38}\mathrm{K}.$ A discrepancy between the two values of $M_0$ is found, suggesting that isospin symmetry is broken in $A=38\mathrm{}$ nuclei. Similar discrepancies occur for $A=34\mathrm{}$ and 42. Experiments for addressing these discrepancies are proposed.

Two cascades of γ rays were discovered in ${}^{113}\mathrm{Pd}$ and ${}^{115}\mathrm{Pd}$ in prompt γ-ray spectroscopy with Gammasphere following heavy-ion induced fission in the reaction ${}^{18}{\mathrm{O}+}^{208}\mathrm{Pb}$ at 91 MeV. Comparison with recently observed band structures in ${}^{109}\mathrm{Pd}$ and ${}^{111}\mathrm{Pd}$ as well as blocking arguments lead to an interpretation of these bands as $\nu h_{11/2}$ bands. This discovery, together with cranked Woods-Saxon and total Routhian surface calculations, indicates that increased rotational frequency stabilizes a prolate but still γ-soft shape in the neutron-rich, even-even Pd isotopes up to ${}^{116}\mathrm{Pd},$ which exhibit very γ-soft nuclear potentials in their respective ground states.