X-ray yields of ${\mathit{K}}^{\mathrm{-}}$-p and ${\mathit{K}}^{\mathrm{-}}$-d atoms are calculated as a function of the target density in order to find an optimum condition for experiments. The dependence of the yields on the energy level shift and absorption width due to the strong interaction is systematically investigated. © 1996 The American Physical Society.

Scattering amplitudes have been extracted from (elastic scattering) neutron-alpha (n-α) differential cross sections below threshold using the constraint that the scattering function is unitary. Real phase shifts have been obtained therefrom. A modification to the Newton iteration method has been used to solve the nonlinear equation that specifies the phase of the scattering amplitude in terms of the complete (0 to 180°) cross section since the condition for a unique and convergent solution by an exact iterated fixed point method, the ‘‘Martin’’ condition, is not satisfied. The results compare well with those found using standard optical model search procedures. Those optical model phase shifts, from both n-α and p-α (proton-alpha) calculations in which spin-orbit effects were included, were used in the second phase of this study, namely to determine the scattering potentials by inversion of that phase shift data. A modified Newton-Sabatier scheme to solve the inverse scattering problem has been used to obtain inversion potentials (both central and spin orbit) for nucleon energies in the range 1 to 24 MeV. The inversion interactions differ noticeably from the Woods-Saxon forms used to give the input phase shifts. Not only do those inversion potentials when used in Schrödinger equations reproduce the starting phase shifts but they are also very smooth, decay rapidly, and are as feasible as the optical model potentials of others to be the local form for interactions deduced by folding realistic two-nucleon g matrices with the density matrix elements of the α particle. © 1996 The American Physical Society.

Absolute branching ratios for the β decay of ${}_{}{}^{57}{}_{}{}^{}\mathrm{Cu}$ to excited states up to 3.3 MeV in ${}_{}{}^{57}{}_{}{}^{}\mathrm{Ni}$ have been determined, including the l-forbidden Gamow-Teller transition to the first excited state in ${}_{}{}^{57}{}_{}{}^{}\mathrm{Ni}$. Four transitions to excited states at 0.768, 1.113, 2.443, and 3.007 MeV are observed in addition to the superallowed decay to the ground state of ${}_{}{}^{57}{}_{}{}^{}\mathrm{Ni}$. The measured branching ratio to the ground state is 89.9 ± 0.8% and the branching ratios to the four excited states are 0.94 ± 0.09%, 8.6 ± 0.6%, 0.17 ± 0.03%, and 0.35 ± 0.04%, respectively. In addition we have measured the ${}_{}{}^{57}{}_{}{}^{}\mathrm{Cu}$ half-life and find it to be 196.3 ± 0.7 ms, which is in good agreement with the most recent measurement. B(GT) values have been extracted from the new results and are compared to shell model calculations. © 1996 The American Physical Society.

A previous study of the ground-state transition of the ${}_{}{}^7{}_{}{}^{}\mathrm{Li}(\overrightarrow{p}, \gamma ){}_{}{}^8{}_{}{}^{}\mathrm{Be}$ reaction at energies of $E_p\left(\mathrm{lab}\right)=80-0\mathrm{}$ keV indicated the possibility of a large $p$-wave capture amplitude in this reaction. A similar $p$-wave component in the ${}_{}{}^7{}_{}{}^{}\mathrm{Be}(p, \gamma ){}_{}{}^8{}_{}{}^{}\mathrm{B}$ reaction could seriously affect the extrapolation used to obtain the astrophysical $S$ factor. The present work examines this possibility by observing the closely related ${}_{}{}^7{}_{}{}^{}\mathrm{Li}(\overrightarrow{p}, {\gamma }_{16.6}){}_{}{}^8{}_{}{}^{}\mathrm{Be}_{}^{*}{}_{}{}^{}$ ($2^{+}$, $T=0+1)$ reaction with polarized protons at and below 80 keV. Experimental data for $\frac{\sigma \left(\theta \right)}{A_0}$ and $A_y\left(\theta \right)$ for capture to the third (16.6 MeV) excited state of 8Be are presented, and the implications discussed.

We use a boost-invariant one-dimensional (cylindrically symmetric) fluid dynamics code to calculate $e^{+}{e}^{-}$ production from ${\rho }^0$ and $\omega$ decay in the central rapidity region of a central S+Au collision at $\sqrt{s}=20\mathrm{}$ GeV/nucleon. We use equations of state with a first-order phase transition between a massless pion gas and quark gluon plasma, with transition temperatures in the range 150-200 MeV. The production cross section at the $\rho$ mass loosely constrains the transition and freeze-out temperatures, and we find that the $m_T$ spectrum is a good thermometer for sufficiently high $T_c$.

Observed enhancements of fusion cross sections at low energies are explained as caused by an underestimate of beam energy due to an overestimate of the stopping energy Ioss.

We calculate the differential cross section of the reaction $d({\pi }^{-}, {\pi }^0)nn$ between 164 and 500 MeV and compare the results with recent data. In general, we obtain good agreement with data except for the backward region at 263 and 371 MeV and the very forward region at 500 MeV. The calculation is performed within a recently proposed extended-three-body model.

Within the framework of a relativistic transport model (ART 1.0) for heavy-ion collisions at AGS energies we study the transverse flow of pions with respect to that of nucleons using two complementary approaches. It is found that in central collisions pions develop a weak flow as a result of the flow of baryon resonances from which they are produced. On the other hand, they have a weak antiflow in peripheral collisions due to the shadowing of spectators. Furthermore, it is shown that both pion flow and antiflow are dominated by those with large transverse momenta.

The structure of nonlocalities implied by the meson exchange dynamics in the nucleon-nucleon interaction is investigated. It is shown that they have a considerable impact on $\mathrm{NN}$ as well as $3N$ observables. It is argued that, for a precise determination of their effects, a sufficiently complete calculation, consistent in the two- and three-body sector, is required.

The charge distributions and their dependence on fragment multiplicity have been studied for the multifragmentation of 30 MeV/nucleon Xe+Au, Cu. For both targets, the charge distributions are approximately independent of the fragment multiplicity $n$. However, a residual systematic dependence on $n$ is detectable at the largest values of the total charge multiplicity $N_c$. Such $n$ dependence obeys a simple scaling law and suggests the presence of an entropic term possibly related to the mechanism of multifragmentation. Thermal scaling between the different bins of $N_c$ seems to occur.

From the observed competition between $M1\mathrm{}$ and $E2\mathrm{}$ $\gamma$ transitions deexciting the states of the two signature partner yrast superdeformed bands in ${}_{}{}^{193}{}_{}{}^{}\mathrm{Tl}$, the $i_{\frac{13}{2}}$ ($\Omega =\frac{5}{2}$) intruder proton orbital is found to have $\frac{(g_K-g_R)K}{Q_0}=0.138\mathrm{}\pm 0.008$. A model dependent value of $g_s^{\mathrm{eff}}=(0.7\mathrm{}\pm 0.2)g_s^{\mathrm{free}}$ is deduced. A saturation of the ${\mathcal{T}}^2$ moments of inertia, at rotational frequency $\hslash \omega >0.32\mathrm{}$ MeV, is observed for the two bands. This feature is discussed in terms of exhausted quasineutron alignment in the presence of substantially reduced quasiproton alignment due to Pauli blocking.

Angular distributions of the tensor analyzing powers $A_{\mathrm{yy}}$ and $A_{\mathrm{zz}}$ have been measured for the ground-state transition in the ${}_{}{}^{93}{}_{}{}^{}\mathrm{Nb}(\overrightarrow{d}, {}_{}{}^3{}_{}{}^{}\mathrm{He}){}_{}{}^{92}{}_{}{}^{}\mathrm{Zr}$ reaction at $E_d=12\mathrm{}$ MeV, and of $A_{\mathrm{zz}}$ for the ground-state transitions in ${}_{}{}^{63}{}_{}{}^{}\mathrm{Cu}(\overrightarrow{d}, {}_{}{}^3{}_{}{}^{}\mathrm{He}){}_{}{}^{62}{}_{}{}^{}\mathrm{Ni}$ at $E_d=8\mathrm{}$ MeV and ${}_{}{}^{89}{}_{}{}^{}\mathrm{Y}(\overrightarrow{d}, {}_{}{}^3{}_{}{}^{}\mathrm{He}){}_{}{}^{88}{}_{}{}^{}\mathrm{Sr}$ at $E_d=10.5\mathrm{}$ MeV. The data are compared with predictions of full finite-range distorted-wave Born approximation (DWBA) calculations from which the asymptotic $D$- to $S$-state ratio, $\eta$, for ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ is extracted to be -0.0386±0.0045±0.0012. The difficulties with a choice of deuteron tensor optical potentials used in the DWBA calculations are discussed.

In order to provide a quantitative test of theoretical calculations incorporating meson-exchange currents and intermediate $\Delta$ resonances, we measure the normal-component spin correlation coefficient $C_{\mathrm{NN}}$, the differential cross section $\frac{d\sigma }{d\Omega }$, and the neutron and proton analyzing powers $A_n$ and $A_p$, each as a function of angle, for $\overrightarrow{n}\overrightarrow{p}\to d\gamma$ at $T_n=183\mathrm{}$ MeV. Our $\overrightarrow{n}\overrightarrow{p}\to d\gamma$ results, combined with the previous cross section and photon asymmetry data collected in the past decade, place quite strong constraints on model calculations. Our data are in excellent agreement with theoretical predictions by Jaus and Woolcock that incorporate meson-exchange and isobar current effects and relativistic corrections, signifying great recent progress in our understanding of these effects in the nucleon-nucleon system.

An exactly Poincaré invariant front form model for the pion-nucleon system is constructed in the space spanned by $|B〉$ and $|\mu B〉$ states where $B=N, \Delta , N^{*}, \dots$ and $\mu =\pi , \eta , \rho , \dots$. A mass-square operator is constructed in the form $M^2=M_0^2+V$ where $M_0$ is a noninteracting mass operator and $V$ is an interaction. Assuming that the spin operator is a free spin operator, the most general form for the interaction $V$ is deduced. A fit to the $\pi N$ elastic scattering amplitudes for pion laboratory kinetic energies up to 700 MeV is carried out, under the assumption that the $\mu B-{\mu }^{\prime }{B}^{\prime }$ interactions are separable.

Precise variational solutions are given for problems involving diverse fermionic and bosonic (N=2–7)-body systems. The trial wave functions are chosen to be combinations of correlated Gaussians, which are constructed from products of the single-particle Gaussian wave packets through an integral transformation, thereby facilitating fully analytical calculations of the matrix elements. The nonlinear parameters of the trial function are chosen by a stochastic technique. The method has proved very efficient, virtually exact, and it seems feasible for any few-body bound-state problems emerging in nuclear or atomic physics.

The tensor analyzing power ${\mathit{A}}_{\mathit{yy}}$ in the symmetric constant relative energy geometry for the dp breakup reaction has been calculated using solutions of the three-nucleon Faddeev equations based on the Argonne AV14, AV18, Bonn-B, Nijm78, Nijm93, NijmI, NijmII, and Paris potentials, as well as the Bonn-B potential in conjunction with the Tucson-Melbourne three-nucleon interaction. The comparison with recent dp data at ${\mathit{E}}_{\mathit{d}}$=94.5 MeV revealed a clear discrepancy in the region where the data exhibit a pronounced structure which is not present in the theoretical results.

Threshold neutral pion photoproduction on light nuclei is studied in the framework of baryon chiral perturbation theory. We obtain a general formula for the electric dipole amplitude in the special case of neutral pion photoproduction on a nucleus. To third order in small momenta, the amplitude is a sum of 2- and 3-body interactions with no undetermined parameters. With reasonable input from the single nucleon sector, our result for neutral pion photoproduction on the deuteron is in agreement with experiment.

The three-nucleon interaction that is implied by the pion and the effective scalar and vector meson exchange components of the nucleon-nucleon interaction arises from the excitation of intermediate nucleon-antinucleon pairs. Using several wave-function models we show that this interaction is repulsive, reducing the calculated binding energy of the trinucleons by about 200–300 keV. The contributions of intermediate N(1440) resonances (and the same meson exchanges) to this three-nucleon interaction are also estimated and shown to be small.

The branching ratios of negative pions and protons due to the weak decays of ${}_{\Lambda }{}^{12}{}_{}{}^{}\mathrm{C}$ and ${}_{\Lambda }{}^{11}{}_{}{}^{}\mathrm{B}$ hypernuclei were measured. The negative pionic decay rates (${\Gamma }_{{\pi }^{-}}$), proton-induced nonmesonic decay rates (${\Gamma }_p$), total nonmesonic decay rates (${\Gamma }_{\mathrm{nm}}$), and ratios of the $\Lambda n\to \mathrm{nn}$ process to the $\Lambda p\to \mathrm{pn}$ process ($\frac{{\Gamma }_n}{{\Gamma }_p}$) were derived from the present measurements combined with previous studies on the mesonic ${\pi }^0$ and total decay rates. The measured ${\Gamma }_{{\pi }^{-}}$ shows that Pauli blocking is less effective than expected due to pion distortion. We found that ${\Gamma }_{\mathrm{nm}}$ is nearly equal to unity in units of the free-space $\Lambda$-decay width. The present results also indicate that ${\Gamma }_n$ is almost twice that of ${\Gamma }_p$. This is in disagreement with calculations based on meson-exchange models in which ${\Gamma }_n$ is strongly suppressed.

Excited states of ${}_{}{}^{132}{}_{}{}^{}\mathrm{Ba}$ were studied in an experiment utilizing the ${}_{}{}^{124}{}_{}{}^{}\mathrm{Sn}$${(}^{13}$C,5n) reaction at a beam energy of 65.5 MeV. The level scheme of ${}_{}{}^{132}{}_{}{}^{}\mathrm{Ba}$ was considerably extended from what was previously known. Evidence is presented for neutron ${\mathit{h}}_{11/2}$ alignments, which are predicted to drive the nucleus to a shape with γ≊-80°. Two strongly coupled ΔI=1 bands were also observed.