Showing papers in "Physical Review C in 1997"

New parametrization for the Lagrangian density of relativistic mean field theory

Abstract: A new parametrization for an effective nonlinear Lagrangian density of relativistic mean field (RMF) theory is proposed, which is able to provide a very good description not only for the properties of stable nuclei but also for those far from the valley of beta stability. In addition the recently measured superdeformed minimum in the {sup 194}Hg nucleus is reproduced with high accuracy. {copyright} {ital 1997} {ital The American Physical Society}

Quantum Monte Carlo calculations of nuclei with A 7

Abstract: We report quantum Monte Carlo calculations of ground and low-lying excited states for nuclei with $Al~7$ using a realistic Hamiltonian containing the Argonne ${v}_{18}$ two-nucleon and Urbana IX three-nucleon potentials. A detailed description of the Green's-function Monte Carlo algorithm for systems with state-dependent potentials is given and a number of tests of its convergence and accuracy are performed. We find that the Hamiltonian being used results in ground states of both ${}^{6}$Li and ${}^{7}$Li that are stable against breakup into subclusters, but somewhat underbound compared to experiment. We also have results for ${}^{6}$He, ${}^{7}$He, and their isobaric analogs. The known excitation spectra of all these nuclei are reproduced reasonably well and we predict a number of excited states in ${}^{6}$He and ${}^{7}$He. We also present spin-polarized one-body and several different two-body density distributions. These are the first microscopic calculations that directly produce nuclear shell structure from realistic interactions that fit $\mathrm{NN}$ scattering data.

{pi}- and K-meson Bethe-Salpeter amplitudes

Abstract: Independent of assumptions about the form of the quark-quark scattering kernel $K$, we derive the explicit relation between the flavor-nonsinglet pseudoscalar-meson Bethe-Salpeter amplitude ${\ensuremath{\Gamma}}_{H}$ and the dressed-quark propagator in the chiral limit. In addition to a term proportional to ${\ensuremath{\gamma}}_{5}$, ${\ensuremath{\Gamma}}_{H}$ necessarily contains qualitatively and quantitatively important terms proportional to ${\ensuremath{\gamma}}_{5}\ensuremath{\gamma}\ensuremath{\cdot}P$ and ${\ensuremath{\gamma}}_{5}\ensuremath{\gamma}\ensuremath{\cdot}\mathrm{kk}\ensuremath{\cdot}P$, where $P$ is the total momentum of the bound state. The axial-vector vertex contains a bound state pole described by ${\ensuremath{\Gamma}}_{H},$ whose residue is the leptonic decay constant for the bound state. The pseudoscalar vertex also contains such a bound state pole and, in the chiral limit, the residue of this pole is related to the vacuum quark condensate. The axial-vector Ward-Takahashi identity relates these pole residues, with the Gell-Mann--Oakes--Renner relation a corollary of this identity. The dominant ultraviolet asymptotic behavior of the scalar functions in the meson Bethe-Salpeter amplitude is fully determined by the behavior of the chiral limit quark mass function, and is characteristic of the QCD renormalization group. The rainbow-ladder Ansatz for $K$, with a simple model for the dressed-quark-quark interaction, is used to illustrate and elucidate these general results. The model preserves the one-loop renormalization group structure of QCD. The numerical studies also provide a means of exploring procedures for solving the Bethe-Salpeter equation without a three-dimensional reduction.

Superheavy nuclei in self-consistent nuclear calculations

Abstract: The shell structure of superheavy nuclei is investigated within various parametrizations of relativistic and nonrelativistic nuclear mean-field models. The heaviest known even-even nucleus ${}_{156}^{264}{\mathrm{Hs}}_{108}$ is used as a benchmark to estimate the predictive value of the models. From that starting point, doubly magic spherical nuclei are searched in the region $Z=110\ensuremath{-}140$ and $N=134$--$298$. They are found at $(Z=114,N=184)$, $(Z=120,N=172)$, or at $(Z=126,N=184)$, depending on the parametrization.

Nuclear incompressibility and density dependent NN interactions in the folding model for nucleus-nucleus potentials

Abstract: A generalized version of density dependence has been introduced into the M3Y effective nucleon-nucleon $(\mathrm{NN})$ interaction that was based on the $G$-matrix elements of the Paris $\mathrm{NN}$ potential. The density dependent parameters have been chosen to reproduce the saturation binding energy and density of normal nuclear matter within a Hartree-Fock scheme, but with various values for the corresponding nuclear incompressibility $K$ ranging from 176 to 270 MeV. We use these new density dependent interactions in the folding model to calculate the real parts of $\ensuremath{\alpha}$-nucleus and nucleus-nucleus optical potentials for those systems where strongly refractive scattering patterns have been observed. These provide some information on the potentials at short distances, where there is a strong overlap of the projectile and target density distributions, and hence where the density dependence of the interaction plays an important role. We try to infer, from careful optical model (OM) analyses, the sensitivity of the scattering data to different $K$ values. Results obtained for elastic $\ensuremath{\alpha}$ scattering on targets ranging from ${}^{12}$C to ${}^{208}$Pb allow us to determine unambiguously that the $K$ value favored in this approach is within the range of 240 to 270 MeV. Similar OM analyses have also been done on measurements of the elastic scattering of ${}^{12}$C+${}^{12}$C, ${}^{16}$O+${}^{12}$C, and ${}^{16}$O+${}^{16}$O at incident energies up to 94 MeV/nucleon. These data were found to be much less sensitive over such a narrow range of $K$ values. This lack of sensitivity is due mainly to the smaller maximum overlap density which occurs for these systems, compared to that which is formed in an $\ensuremath{\alpha}$-nucleus collision. This makes the effects of density dependence less substantial. Another reason is that a small difference between two folded heavy ion potentials can often be compensated for, in part, by a small overall renormalization of one of them. This renormalization is often allowed in optical model analyses, and interpreted, for example, as accounting for a contribution from a higher-order dynamic polarization potential. In an attempt to avoid this ambiguity, some OM analyses of the extensive and accurate data for ${}^{16}$O+${}^{16}$O scattering were done using the unrenormalized folded potentials, together with the explicit addition of a correction term, expressed in terms of cubic splines. This correction term can be interpreted as representing a contribution to the real potential from the dynamic polarization potential. The results of such a ``folding+spline'' analysis suggest a tendency to favor the same $K$ value range that was found in the OM analyses of $\ensuremath{\alpha}$-nucleus scattering.

Spin-isospin structure and pion condensation in nucleon matter

Abstract: We report variational calculations of symmetric nuclear matter and pure neutron matter, using the new Argonne v{sub 18} two-nucleon and Urbana IX three-nucleon interactions. At the equilibrium density of 0.16 fm{sup {minus}3} the two-nucleon densities in symmetric nuclear matter exhibit a short-range spin-isospin structure similar to that found in light nuclei. We also find that both symmetric nuclear matter and pure neutron matter undergo transitions to phases with pion condensation at densities of 0.32 fm{sup {minus}3} and 0.2 fm{sup {minus}3}, respectively. Neither transtion occurs with the Urbana v{sub 14} two-nucleon interaction, while only the transition in neutron matter occurs with the Argonne v{sub 14} two-nucleon interaction. The three-nucleon interaction is required for the transition to occur in symmetric nuclear matter, whereas the transition in pure neutron matter occurs even in its absence. The behavior of the isovector spin-longitudinal response and the pion excess in the vicinity of the transition, and the model dependence of the transition are discussed. {copyright} {ital 1997} {ital The American Physical Society}

Nuclear level density and the determination of thermonuclear rates for astrophysics

Abstract: 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{emdash}as an important ingredient to the statistical model (Hauser-Feshbach){emdash}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{le}A{le}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 {open_quotes}map{close_quotes} for the applicability of the model to reactions of stable and unstable nuclei with neutral and charged particles. {copyright} {ital 1997} {ital The American Physical Society}

Properties of the hypothetical spherical superheavy nuclei

Abstract: Theoretical results on the ground-state properties of the hypothetical spherical superheavy atomic nuclei are presented and discussed. Even-even isotopes of elements Z=104{minus}120 are considered. Certain conclusions are also drawn for odd-A and odd-odd superheavy nuclei. Results obtained earlier for even-even deformed superheavy nuclei with Z=104{minus}114 are given for completeness. Equilibrium deformation, nuclear mass, {alpha}-decay energy, {alpha}-decay half-life, dynamical fission barrier, as well as spontaneous-fission half-life are considered. {beta}-stability of superheavy nuclei is also discussed. The calculations are based on the macroscopic-microscopic model. A multidimensional deformation space describing axially symmetric nuclear shapes is used in the analysis of masses and decay properties of superheavy nuclei. We determined the boundaries of the region of superheavy nuclei which are expected to live long enough to be detected after the synthesis in a present-day experimental setup. {copyright} {ital 1997} {ital The American Physical Society}

Gallium solar neutrino experiments: Absorption cross-sections, neutrino spectra, and predicted event rates

Abstract: Neutrino absorption cross sections for {sup 71}Ga are calculated for all solar neutrino sources with standard energy spectra, and for laboratory sources of {sup 51}Cr and {sup 37}Ar; the calculations include, where appropriate, the thermal energy of fusing solar ions and use improved nuclear and atomic data. The ratio, R, of measured (in GALLEX and SAGE) to calculated {sup 51}Cr capture rate is R=0.95{plus_minus}0.07 (expt)+{sub {minus}0.03}{sup +0.04} (theor). Cross sections are also calculated for specific neutrino energies chosen so that a spline fit determines accurately the event rates in a gallium detector even if new physics changes the energy spectrum of solar neutrinos. Theoretical uncertainties are estimated for cross sections at specific energies and for standard neutrino energy spectra. Standard energy spectra are also presented for pp and CNO neutrino sources in the appendix. Neutrino fluxes predicted by standard solar models, corrected for diffusion, have been in the range 120 SNU to 141 SNU since 1968. {copyright} {ital 1997} {ital The American Physical Society}

Hydrodynamical Description of 200 A GeV/c S+Au Collisions: Hadron and Electromagnetic Spectra

Abstract: We study relativistic S+Au collisions at 200A GeV/c using a hydrodynamical approach. We test various equations of state (EOS{close_quote}s), which are used to describe the strongly interacting matter at densities attainable in the CERN-SPS heavy ion experiments. For each EOS, suitable initial conditions can be determined to reproduce the experimental hadron spectra; this emphasizes the ambiguity between the initial conditions and the EOS in such an approach. Simultaneously, we calculate the resulting thermal photon and dielectron spectra, and compare with experiments. If one allows the excitation of resonance states with increasing temperature, the electromagnetic signals from scenarios with and without phase transition are very similar and are not resolvable within the current experimental resolution. Only EOS{close_quote}s with a few degrees of freedom up to very high temperatures can be ruled out presently. We deduce an upper bound of about 250 MeV for the initial temperature from the single photon spectra of WA80. With regard to the CERES dilepton data, none of the EOS{close_quote}s considered, in conjunction with the standard leading order dilepton rates, succeed in reproducing the observed excess of dileptons below the {rho} peak. Our work, however, suggests that an improved measurement of the photon and dilepton spectra hasmore » the potential to strongly constrain the EOS. {copyright} {ital 1997} {ital The American Physical Society}« less

Excluded volume hadron gas model for particle number ratios in A+A collisions

Abstract: We recapitulate a thermodynamically consistent excluded volume hadron gas model and examine its differences with other ``thermal models'' used in the literature. Preliminary experimental data for particle number ratios in the collisions of $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ at the BNL AGS $(11A\mathrm{GeV}/c)$ and $\mathrm{P}\mathrm{b}+\mathrm{P}\mathrm{b}$ at the CERN SPS $(160A\mathrm{GeV}/c)$ are analyzed. For equal values of the hadron hard-core parameters the excluded volume model gives essentially the ideal gas predictions for the particle number ratios, which is similar to other thermal models. We observe, however, the systematic excess of experimental pion abundances compared to the ideal gas results. This effect can be explained in our model by a smaller pion hard-core volume compared to those of other hadrons. The absolute values for particle number and energy densities at the chemical freezeout are predicted with a simultaneous fit to all these AGS and SPS particle number ratios.

Heavy fragment production cross sections from 1.05 GeV/nucleon 56Fe in C, Al, Cu, Pb, and CH2 targets.

Abstract: We have obtained charge-changing cross sections and partial cross sections for fragmentation of 1.05 GeV/nucleon Fe projectiles incident on H, C, Al, Cu, and Pb nuclei. The energy region covered by this experiment is critical for an understanding of galactic cosmic ray propagation and space radiation biophysics. Surviving primary beam particles and fragments with charges from 12 to 25 produced within a forward cone of half-angle 61 mrad were detected using a silicon detector telescope to identify their charge and the cross sections were calculated after correction of the measured yields for finite target thickness effects. The cross sections are compared to model calculations and to previous measurements. Cross sections for the production of fragments with even-numbered nuclear charges are seen to be enhanced in almost all cases.

Completeness rules for spin observables in pseudoscalar meson photoproduction

Abstract: The number and type of measurements needed to ascertain the amplitudes for pseudoscalar meson photoproduction are analyzed in this paper. It is found that eight carefully selected measurements can determine the four transversity amplitudes without discrete ambiguities. That number of measurements is one less than previously believed. We approach this problem in two distinct ways: (1) solving for the amplitude magnitudes and phases directly, and (2) using a bilinear helicity product formulation to map an algebra of measurements over to the well-known algebra of the 4{times}4 gamma matrices. It is shown that the latter method leads to an alternate proof that eight carefully chosen experiments suffice for determining the transversity amplitudes completely. In addition, Fierz transformations of the gamma matrices are used to develop useful linear and nonlinear relationships between the spin observables. These relationships not only help in finding complete sets of experiments, but also yield important constraints between the 16 observables for this reaction. {copyright} {ital 1997} {ital The American Physical Society}

Spin-dependent neutralino-nucleus scattering for A ∼ 127 nuclei

Abstract: We perform nuclear shell model calculations of the neutralino-nucleus cross section for several nuclei in the A=127 region. Each of the four nuclei considered is a primary target in a direct dark matter detection experiment. The calculations are valid for all relevant values of the momentum transfer. Our calculations are performed in the 3s2d1g{sub 7/2}1h{sub 11/2} model space using extremely large bases, allowing us to include all relevant correlations. We also study the dependence of the nuclear response upon the assumed nuclear Hamiltonian and find it to be small. We find good agreement with the observed magnetic moment as well as other obervables for the four nuclei considered: {sup 127}I, {sup 129,131}Xe, and {sup 125}Te. {copyright} {ital 1997} {ital The American Physical Society}

Classical gluon radiation in ultrarelativistic nucleus-nucleus collisions

Abstract: The classical Yang-Mills equations are solved perturbatively in covariant gauge for a collision of two ultrarelativistic nuclei. The nuclei are taken as ensembles of classical color charges on eikonal trajectories. The classical gluon field is computed in coordinate space up to cubic order in the coupling constant $g$. We construct the Feynman diagrams corresponding to this field and show the equivalence of the classical and diagrammatic approaches. An argument is given which demonstrates that at higher orders in $g$ the classical description of the process breaks down. As an application, we calculate the energy, number, and multiplicity distributions of produced soft gluons and reproduce earlier results by Gunion and Bertsch and by Kovner, McLerran, and Weigert.

Gamow-Teller strength of 90 Nb in the continuum studied via multipole decomposition analysis of the 90 Zr ( p , n ) reaction at 295 MeV

Abstract: The double differential cross sections at ${\ensuremath{\theta}}_{\mathrm{lab}}$ between $0.0\ifmmode^\circ\else\textdegree\fi{}$ and $12.3\ifmmode^\circ\else\textdegree\fi{}$ and the polarization transfer ${D}_{\mathrm{NN}}$ at $0\ifmmode^\circ\else\textdegree\fi{}$ for the ${}^{90}\mathrm{Zr}(p,n)$ reaction are measured at a bombarding energy of 295 MeV. A multipole decomposition technique is applied to the cross sections to extract $L=0$, $L=1$, $L=2$, and $L=3$ contributions. The Gamow-Teller (GT) strength $B(\mathrm{GT})$ in the continuum deduced from the $L=0$ cross section is compared both with the perturbative calculation by Bertsch and Hamamoto and with the second-order random phase approximation calculation by Dro\ifmmode \dot{z}\else \.{z}\fi{}d\ifmmode \dot{z}\else \.{z}\fi{} et al. The sum of $B(\mathrm{GT})$ values up to 50 MeV excitation becomes ${S}_{{\ensuremath{\beta}}^{\ensuremath{-}}}$=28.0\ifmmode\pm\else\textpm\fi{}1.6 after subtracting the contribution of the isovector spin-monopole strength. This ${S}_{{\ensuremath{\beta}}^{\ensuremath{-}}}$ value of 28.0$\ifmmode\pm\else\textpm\fi{}$1.6 corresponds to about (93 $\ifmmode\pm\else\textpm\fi{}$ 5)% of the minimum value of the sum rule $3(N\ensuremath{-}Z)$=30. The usefulness of the polarization transfer observable in the distorted wave impulse approximation is presented.

Spherical proton emitters

Abstract: Various theoretical approaches to proton emission from spherical nuclei are investigated, and it is found that all the methods employed give very similar results. The calculated decay widths are found to be qualitatively insensitive to the parameters of the proton-nucleus potential, i.e., changing the potential parameters over a fairly large range typically changes the decay width by no more than a factor of $\ensuremath{\sim}$3. Proton half-lives of observed heavy proton emitters are, in general, well reproduced by spherical calculations with the spectroscopic factors calculated in the independent quasiparticle approximation. The quantitative agreement with experimental data obtained in our study requires that the parameters of the proton-nucleus potential be chosen carefully. It also suggests that deformed proton emitters will provide invaluable spectroscopic information on the angular momentum decomposition of single-proton orbitals in deformed nuclei.

Ground-state spectrum of light-quark mesons

Abstract: A confining, Goldstone theorem preserving, separable ansatz for the ladder kernel of the two-body Bethe-Salpeter equation is constructed from phenomenologically efficacious $u$, $d$, and $s$ dressed-quark propagators. The simplicity of the approach is its merit. It provides a good description of the ground-state flavor-octet pseudoscalar, vector, and axial-vector meson spectrum facilitates an exploration of the relative importance of various components of the two-body Bethe-Salpeter amplitudes, showing that subleading Dirac components are quantitatively important in the flavor-octet pseudoscalar meson channels, and allows a scrutiny of the domain of applicability of ladder truncation studies. A color-antitriplet diquark spectrum is obtained. The shortcomings of separable Ans\"atze and the ladder kernel are highlighted.

Variation of hadron masses in finite nuclei

Abstract: The quark-meson coupling model, based on a mean-field description of nonoverlapping nucleon bags bound by the self-consistent exchange of $\ensuremath{\sigma}$, $\ensuremath{\omega}$, and $\ensuremath{\rho}$ mesons, is extended to investigate the change of hadron properties in finite nuclei. Relativistic Hartree equations for spherical nuclei have been derived from a relativistic quark model of the structure of bound nucleons and mesons. Using this unified, self-consistent description of both infinite nuclear matter and finite nuclei, we investigate the properties of some closed-shell nuclei and study the changes in the hadron masses of the nonstrange vector mesons, the hyperons, and the nucleon in those nuclei. We find a new, simple scaling relation for the changes of the hadron masses, which can be described in terms of the number of nonstrange quarks in the hadron and the value of the scalar mean field in a nucleus.

Medium-induced parton energy loss in γ +jet events of high-energy heavy-ion collisions

Abstract: The effect of medium-induced parton energy loss on jet fragmentation is studied in high-energy heavy-ion collisions. It is shown that an effective jet fragmentation function can be extracted from the inclusive ${p}_{T}$ spectrum of charged particles in the opposite direction of a tagged direct photon with a fixed transverse energy. We study the modification of the effective jet fragmentation function due to parton energy loss in $\mathrm{AA}$ as compared to $\mathrm{pp}$ collisions, including ${E}_{T}$ smearing from initial-state radiations for the photon-tagged jets. The effective fragmentation function at ${z=p}_{T}{/E}_{T}^{\ensuremath{\gamma}}\ensuremath{\sim}1$ in $\mathrm{pA}$ collisions is shown to be sensitive to the additional ${E}_{T}$ smearing due to initial multiple parton scatterings whose effect must be subtracted out in $\mathrm{AA}$ collisions in order to extract the effective parton energy loss. Jet quenching in deeply inelastic lepton-nucleus scatterings as a measure of the parton energy loss in cold nuclear matter is also discussed. We also comment on the experimental feasibilities of the proposed study at the Relativistic Heavy Ion Collider (RHIC) and Large Hadron Collider (LHC) energies and some alternative measurements such as using ${Z}^{0}$ as a tag at the LHC energy.

Neck formation and deformation effects in a preformed cluster model of exotic cluster decays

Abstract: Using the nuclear proximity approach and the two center nuclear shape parametrization, the interaction potential between two deformed and pole-to-pole oriented nuclei forming a necked configuration in the overlap region is calculated and its role is studied for the cluster decay half-lives. The barrier is found to move to a larger relative separation, with its proximity minimum lying in the neighborhood of the Q value of decay and its height and width reduced considerably. For cluster decay calculations in the preformed cluster model of Malik and Gupta, due to deformations and orientations of nuclei, the (empirical) preformation factor is found to get reduced considerably and agrees nicely with other model calculations known to be successful for their predictions of cluster decay half-lives. Comparison with the earlier case of nuclei treated as spheres suggests that the effects of both deformations and neck formation get compensated by choosing the position of cluster preformation and the inner classical turning point for penetrability calculations at the touching configuration of spherical nuclei.

Yang-Mills radiation in ultrarelativistic nuclear collisions

Abstract: The classical Yang-Mills radiation computed in the McLerran-Venugopalan model is shown to be equivalent to the gluon bremsstrahlung distribution to lowest (g{sup 6}) order in pQCD. The classical distribution is also shown to match smoothly onto the conventional pQCD minijet distribution at a scale k{sub {perpendicular}}{sup 2}{approximately}{chi}, characteristic of the initial parton transverse density of the system. The atomic number and energy dependence of {chi} is computed from available structure function information. The limits of applicability of the classical Yang-Mills description of nuclear collisions at RHIC and LHC energies are discussed. {copyright} {ital 1997} {ital The American Physical Society}

Observational evidence for strange matter in compact objects from the x-ray burster 4U 1820-30

Abstract: We present systematic calculations of the mass-radius (MR) relation of a neutron star (NS) using a large variety of modern equations of state (EOS) of dense matter. The role of strangeness on the EOS and on the MR relation is particularly emphasized. Theoretical results are then compared with the semiempirical MR relation recently extracted for the x-ray burst source 4U 1820-30. Based on this comparison, we propose that the compact object in 4U 1820-30 is a kaon-condensed nucleon star or a strange star.

Neutron-proton correlations in an exactly solvable model

Abstract: We examine isovector and isoscalar neutron-proton correlations in an exactly solvable model based on the algebra SO(8). We look particularly closely at Gamow-Teller strength and double β decay, both to isolate the effects of the two kinds of pairing and to test two approximation schemes: the renormalized neutron-proton quasiparticle random phase approximation (QRPA) and generalized BCS theory. When isoscalar pairing correlations become strong enough a phase transition occurs and the dependence of the Gamow-Teller β+ strength on isospin changes in a dramatic and unfamiliar way, actually increasing as neutrons are added to an N=Z core. Renormalization eliminates the well-known instabilities that plague the QRPA as the phase transition is approached, but only by unnaturally suppressing the isoscalar correlations. Generalized BCS theory, on the other hand, reproduces the Gamow-Teller strength more accurately in the isoscalar phase than in the usual isovector phase, even though its predictions for energies are equally good everywhere. It also mixes T=0 and T=1 pairing, but only on the isoscalar side of the phase transition.

Enhanced T -odd, P -odd electromagnetic moments in reflection asymmetric nuclei

Abstract: Collective $P$- and $T$-odd moments produced by parity and time invariance violating forces in reflection asymmetric nuclei are considered. The enhanced collective Schiff, electric dipole, and octupole moments appear due to the mixing of rotational levels of opposite parity. These moments can exceed single-particle moments by more than 2 orders of magnitude. The enhancement is due to the collective nature of the intrinsic moments and the small energy separation between members of parity doublets. In turn these nuclear moments induce enhanced $T$- and $P$-odd effects in atoms and molecules. A simple estimate is given and a detailed theoretical treatment of the collective $T$-, $P$-odd electric moments in reflection asymmetric, odd-mass nuclei is presented. In the present work we improve on the simple liquid drop model by evaluating the Strutinsky shell correction and include corrections due to pairing. Calculations are performed for octupole deformed long-lived odd-mass isotopes of Rn, Fr, Ra, Ac, and Pa and the corresponding atoms. Experiments with such atoms may improve substantially the limits on time reversal violation.

Study of several double-beta-decaying nuclei using the renormalized proton-neutron quasiparticle random-phase approximation

Abstract: The renormalized proton-neutron quasiparticle random-phase approximation model (RQRPA) has been used to calculate double-\ensuremath{\beta}-decay matrix elements and associated transition half-lives for two-neutrino double \ensuremath{\beta} decay of parent nuclei ${}^{76}\mathrm{Ge},$ ${}^{78}\mathrm{Kr},$ ${}^{82}\mathrm{Se},$ ${}^{96}\mathrm{Zr},$ ${}^{106}\mathrm{Cd},$ and ${}^{130}\mathrm{Te}$ to the ground state and excited one- and two-phonon states of their daughter nuclei. The results are compared to ordinary proton-neutron QRPA and experiments. In addition, the violation of the Ikeda sum rule in the RQRPA is examined and discussed.

Gauge invariant theory of pion photoproduction with dressed hadrons

Abstract: Based on an effective field theory of hadrons in which quantum chromodynamics is assumed to provide the necessary bare cutoff functions, a gauge-invariant theory of pion photoproduction with fully dressed nucleons is developed. The formalism provides consistent dynamical descriptions of {pi}N{r_arrow}{pi}N scattering and {gamma}N{r_arrow}{pi}N production mechanisms in terms of nonlinear integral equations for fully dressed hadrons. Defining electromagnetic currents via the gauging of hadronic n-point Green{close_quote}s functions, dynamically detailed currents for dressed nucleons are introduced. The dressed hadron currents and the pion photoproduction current are explicitly shown to satisfy gauge invariance in a self-consistent manner. Approximations are discussed that make the nonlinear formalism manageable in practice and yet preserve gauge invariance. This is achieved by recasting the gauge conditions for all contributing interaction currents as continuity equations with {open_quotes}surface{close_quotes} terms for the individual particle legs coming into or going out of the hadronic interaction region. General procedures are given that approximate any type of (global) interaction current in a gauge-invariance-preserving manner as a sum of single-particle {open_quotes}surface{close_quotes} currents. It is argued that these prescriptions carry over to other reactions, irrespective of the number or type of contributing hadrons or hadronic systems. {copyright} {ital 1997} {ital The American Physical Society}

Application of contact interactions to Borromean halos

Abstract: ${}^{11}$Li and ${}^{6}$He are described as three-body systems using different approaches. We compare our technique, based on a density-dependent, cutoff, contact interaction between the valence neutrons, with a Faddeev approach which is based on realistic interactions. The ground state properties of a weakly bound two-neutron halo are described fairly well once the contact interaction has been adjusted and calibrated to produce a realistic scattering length and effective range.

The Nucleon-nucleon potential in the 1/N(c) expansion

Abstract: The nucleon-nucleon potential is analyzed using the 1/N{sub c} expansion of QCD. The NN potential is shown to have an expansion in 1/N{sub c}{sup 2}, and the strengths of the leading order central, spin-orbit, tensor, and quadratic spin-orbit forces (including isospin dependence) are determined. Comparison with a successful phenomenological potential (Nijmegen) shows that the large-N{sub c} analysis explains many of the qualitative features observed in the nucleon-nucleon interaction. The 1/N{sub c} expansion implies an effective Wigner supermultiplet symmetry for light nuclei. Results for baryons containing strange quarks are presented in an appendix. {copyright} {ital 1997} {ital The American Physical Society}

Asymptotic normalization coefficients for 10 B → 9 Be + p

Abstract: The differential cross sections for the reactions ${}^{9}\mathrm{Be}{(}^{10}\mathrm{B}{,}^{10}\mathrm{B}{)}^{9}\mathrm{Be}$ and ${}^{9}\mathrm{Be}{(}^{10}\mathrm{B}{,}^{9}\mathrm{Be}{)}^{10}\mathrm{B}$ have been measured at an incident energy of 100 MeV. The elastic scattering data have been used to determine the optical model parameters for the ${}^{9}\mathrm{Be}{+}^{10}\mathrm{B}$ system at this energy. These parameters are then used in distorted-wave Born approximation (DWBA) calculations to predict the cross sections of the ${}^{9}\mathrm{Be}{(}^{10}\mathrm{B}{,}^{9}\mathrm{Be}{)}^{10}\mathrm{B}$ proton exchange reaction, populating the ground and low-lying states in ${}^{10}\mathrm{B}$. By normalizing the theoretical DWBA proton exchange cross sections to the experimental ones, the asymptotic normalization coefficients (ANC's), defining the normalization of the tail of the ${}^{10}\mathrm{B}$ bound state wave functions in the two-particle channel ${}^{9}\mathrm{Be}+p$, have been found. The ANC for the virtual decay ${}^{10}\mathrm{B}(\mathrm{g}.\mathrm{s}.){\ensuremath{\rightarrow}}^{9}\mathrm{Be}+p$ will be used in an analysis of the ${}^{10}\mathrm{B}{(}^{7}\mathrm{Be}{,}^{8}\mathrm{B}{)}^{9}\mathrm{Be}$ reaction to extract the ANC's for ${}^{8}\mathrm{B}{\ensuremath{\rightarrow}}^{7}\mathrm{Be}+p$. These ANC's determine the normalization of the ${}^{7}\mathrm{Be}(p,\ensuremath{\gamma}{)}^{8}\mathrm{B}$ radiative capture cross section at very low energies, which is crucially important for nuclear astrophysics.