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The influence of the isospin-independent, isospin- and momentum-dependent equation of state (EoS), as well as the Coulomb interaction on the pion production in intermediate energy heavy ion collisions (HICs) is studied for both isospin-symmetric and neutron-rich systems. The Coulomb interaction plays an important role in the reaction dynamics, and strongly influences the rapidity and transverse momentum distributions of charged pions. It even leads to the $\pi^-/\pi^+$ ratio deviating slightly from unity for isospin-{\it symmetric} systems. The Coulomb interaction between mesons and baryons is also crucial for reproducing the proper pion flow since it changes the behavior of the directed and the elliptic flow components of pions visibly. The EoS can be better investigated in neutron-rich system if {\it multiple} probes are measured simultaneously. For example, the rapidity and the transverse momentum distributions of the charged pions, the $\pi^-/\pi^+$ ratio, the various pion flow components, as well as the {\it difference} of $\pi^+$-$\pi^-$ flows. A new sensitive observable is proposed to probe the symmetry potential energy at high densities, namely the transverse momentum distribution of the elliptic flow difference [$\Delta v_2^{\pi^+ - \pi^-}(p_t^{\rm c.m.})$].
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arxiv:nucl-th/0509070
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Lectures delivered at the 17th National Nuclear Physics Summer School 2005, Berkeley, CA, June 6-17, 2005.
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arxiv:nucl-th/0510023
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A K-matrix formalism is used to relate single-channel and multi-channel fits. We show how the single-channel formalism changes as new hadronic channels become accessible. These relations are compared to those commonly used to fit pseudoscalar meson photoproduction data.
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arxiv:nucl-th/0510025
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The NA57 experiment at the CERN SPS has measured the production of strange and multi-strange particles in Pb-Pb (and p-Be) collisions at mid-rapidity. The collective dynamics of the collision is studied in the transverse and longitudinal directions as a function of centrality and beam momentum and analysed based on hydrodynamical models. Central-to-peripheral nuclear modification factors at 158 A GeV/c are presented and compared with other measurements and theory.
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arxiv:nucl-th/0510031
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Using a chiral unitary approach for meson-baryon scattering in the strangeness zero sector, where the $N^*(1535)$ and $\Delta^*(1700)$ resonances are dynamically generated, we study the reactions $\gamma p \to \pi^0 \eta p$ and $\gamma p \to \pi^0 K^0 \Sigma^+$ at photon energies at which the final states are produced close to threshold. Among several reaction mechanisms, we find the most important is the excitation of the $\Delta^*(1700)$ state which subsequently decays into a pseudoscalar meson and the $N^*(1535)$. Hence, the reaction provides useful information with which to test current theories of the dynamical generation of the low-lying $1/2^-$ and $3/2^-$ states. Predictions are made for cross sections and invariant mass distributions which can be compared with forthcoming experiments at ELSA.
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arxiv:nucl-th/0510057
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Experimental data on electromagnetic and weak form factors of the nucleon are analyzed in a two-component model with a quark-like intrinsic structure surrounded by a meson cloud. The contribution from strange quarks is discussed and compared with recent data from the G0 Collaboration.
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arxiv:nucl-th/0511004
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We review recent developments in the understanding of meson properties as solutions of the Bethe-Salpeter equation in rainbow-ladder truncation. Included are recent results for the pseudoscalar and vector meson masses and leptonic decay constants, ranging from pions up to c\bar{c} bound states; extrapolation to b\bar{b} states is explored. We also present a new and improved calculation of F_\pi(Q^2) and an analysis of the \pi\gamma\gamma transition form factor for both \pi(140) and \pi(1330). Lattice-QCD results for propagators and the quark-gluon vertex are analyzed, and the effects of quark-gluon vertex dressing and the three-gluon coupling upon meson masses are considered.
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arxiv:nucl-th/0511017
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Separable nucleon-nucleon potentials are calculated using inverse scattering techniques as presented in previously published work. The dependence of the potentials on the momentum cut-off of the scattering phase-shifts is studied. Some comparison is made with the V-low-k potential. The effect of the cut-off on nuclear matter binding energy calculated by standard Brueckner theory is also presented. It is foumd that a cut-off larger than about 4 fm-1 will keep the error to within one Mev around saturation density. While the potentials are cut-off dependent the effective interaction represented by the Brueckner K-matrix is less sensitive to this cut-off. This is in particular found to be the case for the 1S0 state.
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arxiv:nucl-th/0511030
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An admixture of 10-20 % of qqqq\bar q components in the Delta(1232) resonance is shown to reduce the well known underprediction for the decay width for Delta(1232)->N gamma decay by about half and that of the corresponding helicity amplitudes from a factor ~ 1.7 to ~ 1.5. The main effect is due to the quark-antiquark annihilation transitions qqqq\bar q -> qqq gamma, the consideration of which brings the ratio A_{3/2}/A_{1/2} and consequently the E2/M1 ratio R_{EM} into agreement with the empirical value. Transitions between qqqq\bar q components in the resonance and the nucleon qqqq\bar q->qqqq\bar q gamma are shown to enhance the calculated width by only a few percent, as long as the probability of the qqqq\bar q component of the Delta(1232) and the proton is at most ~ 20 %. The transitions qqqq\bar q->qqqq\bar q gamma between the qqqq\bar q components in the Delta(1232) and the proton do not lead to a nonzero value for R_{EM}.
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arxiv:nucl-th/0511053
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Although the neutron (n) does not carry a total electric charge, its charge and magnetization distributions represented in momentum space by the electromagnetic form factors, $F_1^{(n)} (q^2)$ and $F_2^{(n)} (q^2)$, lead to an electromagnetic potential of the neutron. Using this fact, we calculate the electromagnetic corrections to the binding energy, $B_d$, of the deuteron and a one neutron halo nucleus (11Be), by evaluating the neutron-proton and the neutron-charged core (10Be) potential, respectively. The correction to $B_d$ (~9 keV) is comparable to that arising due to the inclusion of the $\Delta$-isobar component in the deuteron wave function. In the case of the more loosely bound halo nucleus, 11Be, the correction is close to about 2 keV.
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arxiv:nucl-th/0511078
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The density functional theory of nuclear structure provides a many-particle wave function that is useful for static properties, but an extension of the theory is necessary to describe correlation effects or other dynamic properties. Here we propose a procedure to extend the theory by mapping the properties of the self-consistent mean-field Hamiltonian onto an effective shell-model Hamiltonian with two-body interactions. In this initial study, we consider the sd-shell nuclei Ne-20, Mg-24, Si-28, and Ar-36. Our first application is in the framework of the USD shell-model Hamiltonian, using its mean-field approximation to construct an effective Hamiltonian and partially recover correlation effects. We find that more than half of the correlation energy is due to the quadrupole interaction. We then follow a similar procedure but using the SLy4 Skyrme energy functional as our starting point and truncating the space to the spherical $sd$ shell. The constructed shell-model Hamiltonian is found to satisfy minimal consistency requirements to reproduce the properties of the mean-field solution. The quadrupolar correlation energies computed with the mapped Hamiltonian are reasonable compared with those computed by other methods.
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arxiv:nucl-th/0512031
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It is shown that isospin-breaking corrections to the pion-deuteron scattering length can be very large, because of the vanishing of the isospin-symmetric contribution to this scattering length at leading order in chiral perturbation theory. We further demonstrate that these corrections can explain the bulk of the discrepancy between the recent experimental data on pionic hydrogen and pionic deuterium. We also give the first determination of the electromagnetic low-energy constant f1.
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arxiv:nucl-th/0512035
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By means of the mixed representation RPA based on the Skyrme-Hartree-Fock mean field, we investigate low-frequency octupole excitations built on the superdeformed (SD) states in the N=Z nuclei around 40Ca and the neutron-rich Sulfur isotopes. The RPA calculation is carried out fully self-consistently on the three-dimensional Cartesian mesh in a box, and yields a number of low-frequency octupole vibrations built on the SD states in 32S, 36Ar, 40Ca and 44Ti. In particular, a strongly collective K^\pi=1^- octupole vibration is suggested to appear on top of the SD state in 40Ca. For 48,50S close to the neutron drip line, we find that the low-lying state created by the excitation of a single neutron from a loosely bound low Omega level to a high Omega resonance level acquires an extremely strong octupole transition strength due to the spatially very extended structure of the particle-hole wave functions.
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arxiv:nucl-th/0512058
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Fully-microscopic No-core Shell Model (NCSM) calculations of all stable $s$ and $p$ shell nuclei are used to determine realistic $NN$ interaction JISP16 describing not only the two-nucleon data but the binding energies and spectra of nuclei with $A\leq 16$ as well. The JISP16 interaction, providing rapid convergence of the NCSM calculations, is obtained in an {\em ab exitu} approach by phase-equivalent transformations of the JISP6 $NN$ interaction.
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arxiv:nucl-th/0512105
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A theory of the competition between fusion and quasi-fission in a heavy fusing system is proposed, which is based on a master equation and the two-center shell model. Fusion and quasi-fission arise from a diffusion process in an ensemble of nuclear shapes, each of which evolves towards the thermal equilibrium. The master equation describes the diffusion of the nuclear shapes due to quantum and thermal fluctuations. Other crucial physical effects like dissipation, ground-state shell effects, diabatic effects and rotational effects are also incorporated into the theory. The fusing system moves in a dynamical (time-dependent) collective potential energy surface which is initially diabatic and gradually becomes adiabatic. The microscopic ingredients of the theory are obtained with a realistic two-center shell model based on Woods-Saxon potentials. Numerical calculations for several reactions leading to $^{256}$No are discussed. Among other important conclusions, the results indicate that (i) the diabatic effects play a very important role in the onset of fusion hindrance for heavy systems, and (ii) very asymmetric reactions induced by closed shell nuclei seem to be the best suited to synthesize the heaviest compound nuclei.
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arxiv:nucl-th/0601042
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We have developed a model to describe the interactions of neutrinos with nucleons and nuclei, focusing on the region of the quasielastic and Delta(1232) peaks. We describe neutrino nucleon collisions with a fully relativistic formalism which incorporates state-of-the-art parametrizations of the form factors for both the nucleon and the N-Delta transition. The model has then been extended to finite nuclei, taking into account nuclear effects such as Fermi motion, Pauli blocking (both within the local density approximation), nuclear binding and final state interactions. The in-medium modification of the Delta resonance due to Pauli blocking and collisional broadening have also been included. Final state interactions are implemented by means of the Boltzmann-Uehling-Uhlenbeck (BUU) coupled-channel transport model. Results for charged current inclusive cross sections and exclusive channels as pion production and nucleon knockout are presented and discussed.
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arxiv:nucl-th/0601103
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It was recently suggested that the error with respect to experimental data in nuclear mass calculations is due to the presence of chaotic motion. The theory was tested by analyzing the typical error size. A more sensitive quantity, the correlations of the mass error between neighboring nuclei, is studied here. The results provide further support to this physical interpretation.
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arxiv:nucl-th/0602041
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We consider interacting Fermi systems close to the unitary regime and compute the corrections to the energy density that are due to a large scattering length and a small effective range. Our approach exploits the universality of the density functional and determines the corrections from the analyical results for the harmonically trapped two-body system. The corrections due to the finite scattering length compare well with the result of Monte Carlo simulations. We also apply our results to symmetric neutron matter.
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arxiv:nucl-th/0602050
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Nuclear forces violating parity and time reversal invariance (${\cal P},{\cal T}$-odd) produce ${\cal P},{\cal T}$-odd nuclear moments, for example, the nuclear Schiff moment. In turn, this moment can induce the electric dipole moment in the atom. The nuclear Schiff moment is predicted to be enhanced in nuclei with static quadrupole and octupole deformation. The analogous suggestion of the enhanced contribution to the Schiff moment from the soft collective quadrupole and octupole vibrations in spherical nuclei is tested in this article in the framework of the quasiparticle random phase approximation with separable quadrupole and octupole forces applied to the odd $^{217-221}$Ra and $^{217-221}$Rn isotopes. We confirm the existence of the enhancement effect due to the soft modes. However, in the standard approximation the enhancement is strongly reduced by a small weight of the corresponding "particle + phonon" component in a complicated wave function of a soft nucleus. The perspectives of a better description of the structure of heavy soft nuclei are discussed.
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arxiv:nucl-th/0602051
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The rapidity dependence of the single- and double- neutron to proton ratios of nucleon emission from isospin-asymmetric but mass-symmetric reactions Zr+Ru and Ru+Zr at energy range $100 \sim 800$ A MeV and impact parameter range $0\sim 8$ fm is investigated. The reaction system with isospin-asymmetry and mass-symmetry has the advantage of simultaneously showing up the dependence on the symmetry energy and the degree of the isospin equilibrium. We find that the beam energy- and the impact parameter dependence of the slope parameter of the double neutron to proton ratio ($F_D$) as function of rapidity are quite sensitive to the density dependence of symmetry energy, especially at energies $E_b\sim 400$ A MeV and reduced impact parameters around 0.5. Here the symmetry energy effect on the $F_D$ is enhanced, as compared to the single neutron to proton ratio. The degree of the equilibrium with respect to isospin (isospin mixing) in terms of the $F_D$ is addressed and its dependence on the symmetry energy is also discussed.
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arxiv:nucl-th/0603050
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The experimental level structure of 134Sb is compared with the results of a shell-model calculation in which the two-body matrix elements of the effective interaction have been derived from the CD-Bonn nucleon-nucleon potential. The experimental data, including the very low-lying first-excited 1- state, are remarkably well reproduced by the theory. The results of this paper complement those of our previous studies on 135Sb and 134Sn, showing that our effective interaction is well suited to describe 132Sn neighbors beyond N=82. The various terms which contribute to the matrix elements of the proton-neutron effective interaction are examined and their relative importance is evidenced.
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arxiv:nucl-th/0603074
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A variety of physical phenomena can lead to viscous effects. In this talk we review several sources of shear and bulk viscosity with an emphasis on the bulk viscosity associated with chiral restoration. We show that in the limit of a second order phase transition, the viscosity peaks in a singularity at the critical point.
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arxiv:nucl-th/0604007
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In medium T-matrix calculations for symmetric nuclear matter at zero and finite temperatures are presented. The internal energy is calculated from the Galitskii-Koltun's sum rule and from the summation of the diagrams for the interaction energy. The pressure at finite temperature is obtained from the generating functional form of the thermodynamic potential. The entropy at high temperature is estimated and compared to expressions corresponding to a quasiparticle gas.
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arxiv:nucl-th/0604030
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The properties of spin polarized neutron matter are studied both at zero and finite temperature using the D1 and the D1P parameterizations of the Gogny interaction. The results show two different behaviors: whereas the D1P force exhibits a ferromagnetic transition at a density of $\rho_c \sim 1.31$ fm$^{-3}$ whose onset increases with temperature, no sign of such a transition is found for D1 at any density and temperature, in agreement with recent microscopic calculations.
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arxiv:nucl-th/0604058
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The energy dependence of the reactions pp -> p Lambda K+ and pp -> p Sigma0 K+ and the ratio R(Lambda/Sigma0} is studied in a constituent quark-gluon model, including the excitation of the baryon resonances N*(1650), N*(1710) and N*(1720) near the Lambda/Sigma0 thresholds. Representing the baryons as quark-diquark objects, the energy dependent ratio Lambda/Sigma0, which is qualitatively reproduced up to excess energies of 60 MeV above threshold, provides detailed information on the momentum spectrum of axial diquarks in the proton and the Sigma0.
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arxiv:nucl-th/0604059
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We address an actual problem of baryon-resonance dominated meson-exchange processes in the low GeV regime, i.e. the phase and the structure of meson-NN* transition vertices. Our starting point is a quark-diquark model for the baryons (obeying approximate covariance; the mesons are kept as elementary objects), together with the relative phases for the NN vertices, as determined from low energy NN scattering. From the explicit representation of the N and N* baryons, we exemplify the derivation of the coupling constants and form factors of the NN*(1535,1/2-)transition vertices for pseudo-scalar, scalar and vector mesons.
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arxiv:nucl-th/0604061
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Following the prediction by Akaishi and Yamazaki of relatively narrow $\bar K$-nuclear states, deeply bound by over 100 MeV where the main decay channel $\bar K N \to \pi \Sigma$ is closed, several experimental signals in stopped $K^-$ reactions on light nuclei have been interpreted recently as due to such states. In this talk I review (i) the evidence from $K^-$-atom data for a {\it deep} $\bar K$-nucleus potential, as attractive as $V_{\bar K}(\rho_0) \sim -(150 - 200)$ MeV at nuclear matter density, that could support such states; and (ii) the theoretical arguments for a {\it shallow} potential, $V_{\bar K}(\rho_0) \sim -(40 - 60)$ MeV. I then review a recent work by Mare\v{s}, Friedman and Gal in which $\bar K$-nuclear bound states are generated dynamically across the periodic table, using a RMF Lagrangian that couples the $\bar K$ to the scalar and vector meson fields mediating the nuclear interactions. Substantial polarization of the core nucleus is found for light nuclei, with central nuclear densities enhanced by almost a factor of two. The binding energies and widths calculated in this dynamical model differ appreciably from those calculated for a static nucleus. These calculations provide a lower limit of $\Gamma_{\bar K} \sim 50 \pm 10$ MeV on the width of nuclear bound states for $\bar K$ binding energy in the range $B_{\bar K} = 100 - 200$ MeV.
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arxiv:nucl-th/0604067
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It is shown that the experimentally observed decrease of the nuclear symmetry energy with the increasing centrality or the excitation energy in isotopic scaling analyses of heavy-ion reactions can be well understood analytically within a degenerate Fermi gas model. The evolution of the symmetry energy is found to be mainly due to the variation in the freeze-out density rather than temperature. The isoscaling analyses are useful for probing the interaction part of the nuclear symmetry energy, provided that both the freeze-out temperature and density of the fragments can be inferred simultaneously from the experiments.
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arxiv:nucl-th/0605002
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We discuss convergence issues as well as short distance constraints on the deuteron wave functions based on chiral perturbation theory relevant to pion deuteron scattering. Non-analytical terms arise in the multiple scattering series for the pion-deuteron scattering length limiting the accuracy of the calculations. This result resembles similar findings in the structure of the NN interaction. The effects are found not to be numerically large. The iso-scalar $\pi N $ scattering length from the iso-vector one and the $\pi d$ scattering length yields values compatible with the experimental number and with much smaller errors.
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arxiv:nucl-th/0605078
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11Li is studied within a three-body model 9Li+n+n where the core is allowed to be deformed and/or excite. In particular, we include reorientation couplings and couplings between the two bound states of 9Li. Contrary to the other examples studied within this model, we find that core excitation does not affect the structure of 11Li significantly. Reorientation couplings of the deformed 9Li can change the ground state of 11Li from a predominantly two neutron s1/2^2 configuration into a p1/2^2. In addition, we see no evidence for the existence of significant d-wave strength in its ground state, as opposed to the prediction by shell model. A comparison with shell model is presented.
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arxiv:nucl-th/0606048
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Predictions of the existence of well-defined deeply bound pionic atom states for heavy nuclei and the eventual observation of such states by the (d,3He) reaction have revived interest in the pion-nucleus interaction at threshold and in its relation to the corresponding pion-nucleon interaction. Explanation of the 'anomalous' s-wave repulsion in terms of partial restoration of chiral symmetry and/or in terms of energy-dependence effects have been tested in global fits to pionic atom data and in a recent dedicated elastic scattering experiment. The role of neutron density distributions in this context is discussed in detail for the first time.
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arxiv:nucl-th/0607049
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Isospin effects on the optical potentials of kaons and antikaons in dense hadronic matter are investigated using a chiral SU(3) model. These effects are important for asymmetric heavy ion collision experiments. In the present work the dispersion relations are derived for kaons and antikaons, compatible with the low energy scattering data, within our model approach. The relations result from the kaonic interactions with the nucleons, vector mesons and scalar mesons in the asymmetric nuclear matter. The isospin asymmetry effects arising from the interactions with the vector-isovector $\rho$- meson as well as the scalar isovector $\delta$ mesons are considered. The density dependence of the isospin asymmetry is seen to be appreciable for the kaon and antikaon optical potentials. This can be particularly relevant for the future accelerator facility FAIR at GSI, where experiments using neutron rich beams are planned to be used in the study of compressed baryonic matter.
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arxiv:nucl-th/0607050
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Two solvable Hamiltonians for describing the dynamic gamma deformation, are proposed. The limiting case of each of them is the X(5) Hamiltonian. Analytical solutions for both energies and wave functions, which are periodic in $\gamma$, are presented in terms of spheroidal and Mathieu functions, respectively. Moreover, the gamma depending factors of the transition operator can be treated.
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arxiv:nucl-th/0607064
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The possibility of synthesizing a doubly magic superheavy nucleus, $^{298}114_{184}$, is investigated on the basis of fluctuation-dissipation dynamics. In order to synthesize this nucleus, we must generate more neutron-rich compound nuclei because of the neutron emissions from excited compound nuclei. The compound nucleus $^{304}114$ has two advantages to achieving a high survival probability. First, because of small neutron separation energy and rapid cooling, the shell correction energy recovers quickly. Secondly, owing to neutron emissions, the neutron number of the nucleus approaches that of the double closed shell and the nucleus obtains a large fission barrier. Because of these two effects, the survival probability of $^{304}114$ does not decrease until the excitation energy $E^{*}= 50$ MeV. These properties lead to a rather high evaporation reside cross section.
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arxiv:nucl-th/0609043
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We show that dynamical deformation effects play an important role in fusion reactions involving the $^{64}$Ni nucleus, in particular the $^{64}$Ni+$^{132}$Sn system. We calculate fully microscopic interaction potentials and the corresponding subbarrier fusion cross sections.
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arxiv:nucl-th/0609071
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We investigate the composition and the equation of state of the kaon condensed phase in neutrino-free and neutrino-trapped star matter within the framework of the Brueckner-Hartree-Fock approach with three-body forces. We find that neutrino trapping shifts the onset density of kaon condensation to a larger baryon density, and reduces considerably the kaon abundance. As a consequence, when kaons are allowed, the equation of state of neutrino-trapped star matter becomes stiffer than the one of neutrino free matter. The effects of different three-body forces are compared and discussed. Neutrino trapping turns out to weaken the role played by the symmetry energy in determining the composition of stellar matter, and thus reduces the difference between the results obtained by using different three-body forces.
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arxiv:nucl-th/0610037
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With the aim of extracting information on the shift of the $\omega$ mass in the nuclear medium we analyze data obtained at ELSA from where claims for evidence of a mass shift of the $\omega$ have been made. We develop a Monte Carlo simulation code which takes into account the possible reactions in the experimental set up of $(\gamma ~ A \to \pi^0 \gamma ~X)$ in the vicinity of the $\omega$ production region with subsequent $\omega \to \pi^0 \gamma$ decay. We compare our results with experiment for the distribution of $\pi^0 \gamma$ invariant masses and conclude that the distribution is compatible with an enlarged $\omega$ width of about 90 MeV at nuclear matter density and no shift in the mass. This change in the width would be compatible with the preliminary results obtained from the transparency ratio in the A dependence of $\omega$ production. The discrepancy of the present conclusions with former claims of an evidence for a shift of the $\omega$ mass stem from a different choice of background which is discussed in the paper.
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arxiv:nucl-th/0610067
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This Dyson-Schwinger equation (DSE) aperc,u highlights recent applications to mesons. It reports features of, and results for, pseudoscalar and scalar bound-state residues in vacuum polarisations, and exhibits how a restoration of chiral symmetry in meson trajectories could be manifest in a relationship between them. It also touches on nucleon studies, emphasising the importance of both scalar and axial-vector diquark correlations, and reporting the calculation of mu_n G_E^n(Q^2)/G_M^n(Q^2). The value of respecting symmetries, including Poincare' covariance, is stressed.
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arxiv:nucl-th/0610080
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An extension of the single-freeze-out model with thermal and geometric parameters dependent on the spatial rapidity, $\alpha_\parallel$, is used to describe the rapidity and transverse-momentum spectra of pions, kaons, protons, and antiprotons measured at RHIC at $\sqrt{s_{NN}}=200 {\rm GeV}$ by the BRAHMS collaboration. {\tt THERMINATOR} is used to perform the necessary simulation, which includes all resonance decays. The result of the fit to the rapidity spectra in the range of the BRAHMS data is the expected growth of the baryon and strange chemical potentials with the magnitude of $\alpha_\parallel$, while the freeze-out temperature is kept fixed. The value of the baryon chemical potential at $\alpha_\parallel \sim 3$, which is the relevant region for particles detected at the BRAHMS forward rapidity $y \sim 3$, is about $200 {\rm GeV}$, {\em i.e.} lies in the range of the values obtained for the highest SPS energy. The chosen geometry of the fireball has a decreasing transverse size as the magnitude of $\alpha_\parallel$ is increased, which also corresponds to decreasing transverse flow. This feature is verified by reproducing the transverse momentum spectra of pions and kaons at various rapidities. The strange chemical potential obtained from the fit to the $K^+/K^-$ ratio is such that the local strangeness density in the fireball is compatible with zero. The resulting rapidity spectra of net protons are described qualitatively in the model. As a result of the study, the knowledge of the ``topography'' of the fireball is achieved, making other calculations possible. As an example, we give predictions for the rapidity spectra of hyperons.
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arxiv:nucl-th/0610083
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We calculate at two-loop order in chiral perturbation theory the electromagnetic corrections to the two-pion exchange nucleon-nucleon interaction that is generated by the isovector spin-flip $\pi\pi NN$ contact-vertex proportional to the large low-energy constant $c_4\simeq 3.4 $GeV$^{-1}$. We find that the respective $2\pi\gamma$-exchange potentials contain sizeable isospin-breaking components which reach up to -4% of corresponding isovector $2\pi$-exchange potentials. The typical values of these novel charge-independence breaking spin-spin and tensor potentials are $-0.11 $MeV and $0.09 $MeV, at a nucleon distance of $r=m_\pi^{-1}=1.4 $fm. The charge-symmetry breaking spin-spin and tensor potentials come out a factor of 2.4 smaller. Our analytical results for these presumably dominant isospin-violating spin-spin and tensor NN-forces are in a form such that they can be easily implemented into phase-shift analyses and few-body calculations.
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arxiv:nucl-th/0610089
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We construct a hadronic kinetic model for description of excitation functions of multiplicity ratios K+/pi+, K-/pi-, and Lambda/pi. It is shown that the model is able to describe data rather well under the assumption that the total lifespan of the fireball is decreasing function of the collision energy for SPS energies above 30 AGeV. Thus in order to identify the onset of deconfinement the proposed model will have to be checked against other kinds of data until hadronic description can be safely falsified.
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arxiv:nucl-th/0610122
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A model in which the soft collisions of the nucleon are described in terms of interactions of its two constituents (a quark and a diquark) is proposed. When adjusted to describe precisely the elastic proton-proton scattering data and supplemented with the idea of wounded constituents, the model accounts rather well for the centrality dependence of particle production in the central rapidity region at RHIC energies.
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arxiv:nucl-th/0611021
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We use the Bethe-Salpeter equation in rainbow-ladder truncation to calculate the ground state mesons from the chiral limit to bottomonium, with an effective interaction that was previously fitted to the chiral condensate and pion decay constant. Our results are in reasonable agreement with the data, as are the vector and pseudoscalar decay constants. The meson mass differences tend to become constant in the heavy-quark limit. We also present calculations for the pion and rho electromagnetic form factors, and for the single-quark form factors of the \eta_c and J/\psi.
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arxiv:nucl-th/0611057
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We investigate the centrality dependence of the pT-correlations in the event-by-event analysis of relativistic heavy-ion collisions at RHIC made recently by the PHENIX and STAR Collaborations. We notice that sigma^2 dynamical scales to a very good accuracy with the inverse number of the produced particles, n. This scaling can be naturally explained by formation of clusters. We discuss the nature of clusters and provide numerical estimates of correlations coming from resonance decays, which are tiny, and a model where particle are emitted from local thermalized sources moving at the same collective velocity. This "lumped cluster" model can explain the data when on the average 6-15 particles are contained in a cluster. We also point out simple relations of the popular correlation measures to the covariance, which arise under the assumptions (well holding at RHIC) that the distributions are sharply peaked in n and that the dynamical compared to statistical fluctuations are small.
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arxiv:nucl-th/0611069
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Pairing properties of even-even superheavy N=184 isotones are studied within the Skyrme-Hartree-Fock+BCS approach. In the particle-hole channel we take the Skyrme energy density functional SLy4, while in the particle-particle channel we employ the seniority pairing force and zero-range delta-interactions with different forms of density dependence. We conclude that the calculated static fission trajectories weakly depend on the specific form of the delta-pairing interaction. We also investigate the impact of triaxiality on the inner fission barrier and find a rather strong Z dependence of the effect.
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arxiv:nucl-th/0611076
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We summarize the findings of our Working Group, which discussed progress in the understanding of Chiral Dynamics in the A=2, 3, and 4 systems over the last three years. We also identify key unresolved theoretical and experimental questions in this field.
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arxiv:nucl-th/0611084
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The structure of Omega-pi state with isospin I=1 and spin-parity J^p=3/2^- are dynamically studied in both the chiral SU(3) quark model and the extended chiral SU(3) quark model by solving a resonating group method (RGM) equation. The model parameters are taken from our previous work, which gave a satisfactory description of the energies of the baryon ground states, the binding energy of the deuteron, the nucleon-nucleon (NN) scattering phase shifts, and the hyperon-nucleon (YN) cross sections. The calculated results show that the Omega-pi state has an attractive interaction, and in the extended chiral SU(3) quark model such an attraction can make for an Omega-pi quasi-bound state with the binding energy of about several MeV.
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arxiv:nucl-th/0612007
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Modern cosmic ray transport codes, that are capable of use for a variety of applications, need to include all significant atomic, nuclear and particle reactions at a variety of energies. Lepton pair production from nucleus-nucleus collisions has not been included in transport codes to date. Using the methods of Baur, Bertulani and Baron, the present paper provides estimates of electron-positron pair production cross sections for nuclei and energies relevant to cosmic ray transport. It is shown that the cross sections are large compared to other typical processes such as single neutron removal due to strong or electromagnetic interactions. Therefore lepton pair production may need to be included in some transport code applications involving MeV electrons.
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arxiv:nucl-th/0612054
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The $pp \to nK^+\Sigma^+$ reaction is a very good isospin 3/2 filter for studying $\Delta^{++*}$ decaying to $K^+\Sigma^+$. With an effective Lagrangian approach, contributions from a previous ignored sub-$K^+\Sigma^+$-threshold resonance $\Delta^{++*}(1620)1/2^-$ are fully included in addition to those already considered in previous calculations. It is found that the $\Delta^{++*}(1620)1/2^-$ resonance gives an overwhelmingly dominant contribution for energies very close to threshold, with a very important contribution from the t-channel $\rho$ exchange. This solves the problem that all previous calculations seriously underestimate the near-threshold cross section by order(s) of magnitude. Many important implications of the results are discussed.
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arxiv:nucl-th/0701021
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We review some recent experimental and theoretical work on the correlation among hadrons produced at intermediate $p_T$ at RHIC. The topics include: forward and backward asymmetry with and without trigger at mid-rapidity, associated-particle distribution on the near side, the $\Omega$ puzzle and its solution, associated particles on the away side, and two-jet recombination at LHC.
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arxiv:nucl-th/0701051
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In the last few years, the low-momentum nucleon-nucleon (NN) interaction V-low-k derived from free-space NN potentials has been successfully used in shell-model calculations. V-low-k is a smooth potential which preserves the deuteron binding energy as well as the half-on-shell T-matrix of the original NN potential up to a momentum cutoff Lambda. In this paper we put to the test a new low-momentum NN potential derived from chiral perturbation theory at next-to-next-to-next-to-leading order with a sharp low-momentum cutoff at 2.1 fm-1. Shell-model calculations for the oxygen isotopes using effective hamiltonians derived from both types of low-momentum potential are performed. We find that the two potentials show the same perturbative behavior and yield very similar results.
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arxiv:nucl-th/0701065
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Applying the unitary clothing transformation method in the model of charged spinless nucleons and neutral mesons interacting via the three-linear Yukawa-type coupling, the expression for the charge shift in the third order in the coupling constant is derived. Being determined off the energy shell, the ex-pression can be reduced on the energy shell to the explicitly covariant form, providing the independence of the particle momenta. Comparison with the cor-responding result of the Dyson covariant perturbation theory is performed by es-tablishing the link between the old-fashioned perturbation theory and the cloth-ing approach.
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arxiv:nucl-th/0701071
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The first order self-energy corrections of the kaon in the symmetric nuclear matter are calculated from kaon-nucleon scattering matrix elements using a chiral Lagrangian within the framework of relativistic mean field approximation. It shows that the effective mass and the potential of K^+ meson are identical with those of K^- meson in the nuclear matter, respectively. The effective mass of the kaon in the nuclear matter decreases with the nuclear density increasing, and is not relevant to the kaon-nucleon Sigma term. The kaon-nucleus potential is positive and increases with the nuclear density. Moreover, the influence of the resonance $\Lambda(1405)$ on the $K^-$-nucleus potential due to the re-scattering term is discussed. Our results indicate the K^- meson could not be bound in the nuclei even if the contribution of $\Lambda(1405)$ resonance is considered.
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arxiv:nucl-th/0701085
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The effects of different forms of the sound-velocity function c_s(T) on the hydrodynamic evolution of matter created in the central region of ultra-relativistic heavy-ion collisions are studied. At high temperatures (above the critical temperature T_c) we use the sound velocity function obtained from the recent lattice simulations of QCD, whereas at low temperatures we use the ideal hadron gas model. At moderate temperatures different interpolations between those two results are employed. They are characterized by different values of the local maximum (at T = 0.4 T_c) and local minimum (at T=T_c). The extreme values are chosen in such a way that at high temperature all considered sound-velocity functions yield the entropy density consistent with the lattice simulations of QCD. We find that the presence of a distinct minimum of the sound velocity leads to a very long (~ 20 fm/c) evolution time of the system. Since such long evolution times are not compatible with the recent estimates based on the HBT interferometry, we conclude that the hydrodynamic description becomes adequate if the QCD cross-over phase transition renders the smooth temperature variations of the sound velocity, with a possible shallow minimum at T_c where the values of c_s^2(T) remain well above 0.1.
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arxiv:nucl-th/0702030
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The four major approximation schemes devised to study the modification of jets in dense matter are outlined. The comparisons are restricted to basic assumptions and approximations made in each case and the calculation methodology used. Emergent underlying similarities between apparently disparate methods brought about by the approximation schemes are exposed. Parameterizations of the medium in each scheme are discussed in terms of the transport coefficient $\hat{q}$. Discrepancies between the estimates obtained from the four schemes are discussed. Recent developments in the basic theory and phenomenology of energy loss are highlighted.
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arxiv:nucl-th/0702066
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The superscaling observed in inclusive electron scattering is described within the dilute Fermi gas model with interaction between the particles. The comparison with the relativistic Fermi gas (RFG) model without interaction shows an improvement in the explanation of the scaling function $f(\psi ')$ in the region $\psi ' < -1$, where the RFG result is $f(\psi ') = 0$. It is found that the behavior of $f(\psi ')$ for $\psi ' < -1$ depends on the particular form of the general power-law asymptotics of the momentum distribution $n(k)\sim 1/ k^{4+m}$ at large $k$. The best agreement with the empirical scaling function is found for $m\simeq 4.5$ in agreement with the asymptotics of $n(k)$ in the coherent density fluctuation model where $m = 4$. Thus, superscaling gives information about the asymptotics of $n(k)$ and the NN forces.
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arxiv:nucl-th/0703003
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Cross sections are calculated for neutrino scattering off heavy nuclei at energies below 50 MeV. The theory of Fermi liquid is applied to estimate the rate of neutrino-nucleon elastic and inelastic scattering in a nuclear medium in terms of dynamic form factors. The cross sections, obtained here in a rather simple way, are in agreement with the results of the other much more sophisticated nuclear models. A background rate from the solar neutrino interactions within a large Ge detector is estimated in the above-mentioned approach. The knowledge of the rate is in particular rather important for new-generation large-scale neutrino experiments.
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arxiv:nucl-th/0703036
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We discuss strength of monopole excitation of the ground state to cluster states in light nuclei. We clarify that the monopole excitation to cluster states is in general strong as to be comparable with the single particle strength and shares an appreciable portion of the sum rule value in spite of large difference of the structure between the cluster state and the shell-model-like ground state. We argue that the essential reasons of the large strength are twofold. One is the fact that the clustering degree of freedom is possessed even by simple shell model wave functions. The detailed feature of this fact is described by the so-called Bayman-Bohr theorem which tells us that SU(3) shell model wave function is equivalent to cluster model wave function. The other is the ground state correlation induced by the activation of the cluster degrees of freedom described by the Bayman-Bohr theorem. We demonstrate, by deriving analytical expressions of monopole matrix elements, that the order of magnitude of the monopole strength is governed by the first reason, while the second reason plays a sufficient role in reproducing the data up to the factor of magnitude of the monopole strength. Our explanation is made by analysing three examples which are the monopole excitations to the $0^+_2$ and $0^+_3$ states in $^{16}$O and the one to the $0^+_2$ state in $^{12}$C. The present results imply that the measurement of strong monopole transitions or excitations is in general very useful for the study of cluster states.
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arxiv:nucl-th/0703045
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The flavor content of nucleon form factors is analyzed using two different theoretical approaches. The first is based on a phenomenological two-component model in which the external photon couples to both an intrinsic three-quark structure and a meson cloud via vector-meson dominance. The flavor content of the nucleon form factors is extracted without introducing any additional parameter. A comparison with recent data from parity-violating electron scattering experiments shows a good overall agreement for the strange form factors. A more microscopic approach is that of an unquenched quark model proposed by Geiger and Isgur which is based on valence quark plus glue dominance to which quark-antiquark pairs are added in perturbation. In the original version the importance of $s \bar{s}$ loops in the proton was studied. Here we present the formalism for a new generation of unquenched quark models which, among other extensions, includes the contributions of $u \bar{u}$ and $d \bar{d}$ loops. Finally, we discuss some preliminary results in the closure limit.
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arxiv:nucl-th/0703053
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We present a hybrid equation of state (EoS) for dense matter in which a nuclear matter phase is described within the Dirac-Brueckner-Hartree-Fock (DBHF) approach and a two-flavor quark matter phase is modelled according to a recently developed covariant, nonlocal chiral quark model. We show that modern observational constraints for compact star masses (M ~ 2 M_sun) can be satisfied when a small vector-like four quark interaction is taken into account. The corresponding isospin symmetric EoS is consistent with flow data analyses of heavy ion collisions and points to a deconfinement transition at about 0.55 fm^-3.
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arxiv:nucl-th/0703088
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The paper is the written version of a talk presented at the "VIIth Winter School of Hadronic Physics", held in Folgaria (Trento), Italy, February 10--15, 1992. We intend to illustrate in this lecture the possibilities opening up at machines planned for the nineties for low--energy kaon--nucleon interactions, keeping the focus on the theoretical problems they should help to solve. We shall deal here only with the $\phi$--factory DA$\Phi$NE$^1$ and consider, for brevity, interactions with light, gaseous targets, using gaseous $H_2$ as a benchmark for which to estimate the rates to be expected in a typical apparatus.
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arxiv:nucl-th/9210008
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There have been suggestions to measure atomic parity nonconservation (PNC) along an isotopic chain, by taking ratios of observables in order to cancel complicated atomic structure effects. Precise atomic PNC measurements could make a significant contribution to tests of the Standard Model at the level of one loop radiative corrections. However, the results also depend upon certain features of nuclear structure, such as the spatial distribution of neutrons in the nucleus. To examine the sensitivity to nuclear structure, we consider the case of Pb isotopes using various recent relativistic and non-relativistic nuclear model calculations. Contributions from nucleon internal weak structure are included, but found to be fairly negligible. The spread among present models in predicted sizes of nuclear structure effects may preclude using Pb isotope ratios to test the Standard Model at better than a one percent level, unless there are adequate independent tests of the nuclear models by various alternative strong and electroweak nuclear probes. On the other hand, sufficiently accurate atomic PNC experiments would provide a unique method to measure neutron distributions in heavy nuclei.
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arxiv:nucl-th/9211004
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It is shown that the 1S level hyperfine populations prior to muon capture will be statistical when either target or beam are unpolarised independent of the atomic level at which the hyperfine interaction becomes appreciable. This assertion holds in the absence of magnetic transitions during the cascade and is true because of minimal polarisation after atomic capture and selective feeding during the cascade.
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arxiv:nucl-th/9212007
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Internal target experiments with high quality proton beams allow for a new class of experiments providing null tests of time reversal symmetry in forward scattering. This could yield more stringent limits on T-odd P-even observables. A excellent candidate for such experiments is the proton deuteron system. This system is analyzed in terms of effective T-violating P-conserving nucleon-nucleon interactions and bounds on coupling strengths that might be expected are given.
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arxiv:nucl-th/9302002
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A semi-classical, many-body atomic model incorporating a momentum-dependent Heisenberg core to stabilize atomic electrons is used to study antiproton capture on Helium. Details of the antiproton collisions leading to eventual capture are presented, including the energy and angular momentum states of incident antiprotons which result in capture via single or double electron ionization, i.e. into [He$^{++}\,\bar p$ or He$^{+}\,\bar p$], and the distribution of energy and angular momentum states following the Auger cascade. These final states are discussed in light of recently reported, anomalously long-lived antiproton states observed in liquid He.
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arxiv:nucl-th/9304012
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In this paper we give explicit formulae in momentum and coordinate space for the three-nucleon potentials due to $\rho$ and $\pi$ meson exchange, derived from off-mass-shell meson-nucleon scattering amplitudes which are constrained by the symmetries of QCD and by the experimental data. Those potentials have already been applied to nuclear matter calculations. Here we display additional terms which appear to be the most important for nuclear structure. The potentials are decomposed in a way that separates the contributions of different physical mechanisms involved in the meson-nucleon amplitudes. The same type of decomposition is presented for the $\pi - \pi$ TM force: the $\Delta$, the chiral symmetry breaking and the nucleon pair terms are isolated.
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arxiv:nucl-th/9305017
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A simple two-level model is developed and used to test the properties of effective interactions for performing nuclear structure calculations in truncated model spaces. It is shown that the effective many-body interactions sensitively depend on the choice of the single-particle basis and they appear to be minimized when a self- consistent Hartree-Fock basis is used.
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arxiv:nucl-th/9306014
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The production of antiprotons in proton-nucleus and nucleus-nucleus reactions is calculated within the relativistic BUU approach employing proper selfenergies for the baryons and antiprotons and treating the p-bar annihilation nonperturbatively. The differential cross section for the antiprotons is found to be very sensitive to the p-bar selfenergy adopted. A detailed comparison with the available experimental data for p-nucleus and nucleus-nucleus reactions shows that the antiproton feels a moderately attractive mean-field at normal nuclear matter density which is in line with a dispersive potential extracted from the free annihilation cross section.
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arxiv:nucl-th/9306020
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A model is presented to describe electromagnetically induced two-nucleon emission processes in a shell-model picture. Distortions in the outgoing nucleon waves are accounted for by performing a partial-wave expansion in a real mean-field potential. The antisymmetry condition for the A-body wavefunctions is shown to be naturally preserved. The model is used to calculate ($\gamma$,pn) and ($\gamma$,pp) cross sections off the target nuclei $^{16}$O and $^{12}$C for photon energies ranging from 50 MeV up to the $\bigtriangleup$(1232) isobar threshold. Effects due to the pionic currents and intermediate $\bigtriangleup$ creation are implemented. The impact of the distortions due to the interaction of the outgoing nucleon waves with the (A-2) core is examined. Hadronic form factors are introduced to regularize the $\pi$NN vertices and the sensitivity of the cross section to the pion cut-off mass is examined. The relative contribution of the ($\gamma$,pp) and the ($\gamma$,pn) channel to the total photoabsorption strength is discussed. Further, the photon energy dependence of the ($\gamma$,pp)/($\gamma$,pn) ratio is investigated.
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arxiv:nucl-th/9307004
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We introduce momentum-dependent scalar and vector fields into the Lorentz covariant relativistic BUU- (RBUU-) approach employing a polynomial ansatz for the relativistic nucleon-nucleon interaction. The momentum-dependent parametrizations are shown to be valid up to about 1 GeV/u for the empirical proton-nucleus optical potential. We perform numerical simulations for heavy-ion collisions within the RBUU-approach adopting momentum-dependent and momentum-independent mean-fields and calculate the transverse flow in and perpendicular to the reaction plane, the directivity distribution as well as subthreshold K+-production. By means of these observables we discuss the particular role of the momentum-dependent forces and their implications on the nuclear equation of state. We find that only a momentum-dependent parameter-set can explain the experimental data on the transverse flow in the reaction plane from 150 - 1000 MeV/u and the differential K+-production cross sections at 1 GeV/u at the same time.
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arxiv:nucl-th/9307024
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Gamow-Teller strength functions in full $(pf)^{8}$ spaces are calculated with sufficient accuracy to ensure that all the states in the resonance region have been populated. Many of the resulting peaks are weak enough to become unobservable. The quenching factor necessary to bring into agreement the low lying observed states with shell model predictions is shown to be due to nuclear correlations. To within experimental uncertainties it is the same that is found in one particle transfer and (e,e') reactions. Perfect consistency between the observed $^{48}Ca(p,n)^{48}Sc$ peaks and the calculation is achieved by assuming an observation threshold of 0.75\% of the total strength, a value that seems typical in several experiments
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arxiv:nucl-th/9401010
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Pauli-projected random gaussians are used as a representation to solve the shell model equations. The elements of the representation are chosen by a variational procedure. This scheme is particularly suited to describe cluster formation and cluster decay in nuclei. It overcomes the basis-size problem of the ordinary shell model and the technical difficulties of the cluster-configuration shell model. The model reproduces the $\alpha$-decay width of $^{212}$Po satisfactorily.
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arxiv:nucl-th/9403016
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Scalar and vector interactions, with the scalar interaction coupled to a composite spin-1/2 system so as to cause a shift of its mass, are shown to obey a low-energy theorem which guarantees that the second order interaction due to z-graphs is the same as for a point Dirac particle. Off-shell and contact interactions appropriate to the composite system cancel and this is verified in a model of a composite fermion. The result provides a justification for the use of the Dirac equation as it has been in relativistic nuclear scattering and mean field theories.
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arxiv:nucl-th/9407040
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We study higher-order effects in the electromagnetic production of electron-positron pairs in relativistic heavy ion collisions. Treating the field of the heavy ions as an external field and neglecting the interaction among electrons and positrons, we show that the $N$-pair creation amplitude is the antisymmetrised product of $N$ one-pair creation amplitudes and the vacuum amplitude. Neglecting contributions coming from exchange terms, we show that the total probability for $N$ pairs is approximately a Poisson distribution. We investigate further the structure of the reduced one-pair amplitude, concentrating especially on multiple-particle corrections. We calculate the first of these corrections in second order Magnus theory based on our previous result in second-order Born approximation for impact parameter $b$ zero. Explicit calculations show that the total probability is increased up to 10 \% by this correction for realistic collider parameters. The calculations can also be used to confirm the use of the Poisson distribution for the total probability.
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arxiv:nucl-th/9408009
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It is shown that a consistent description of magnetic dipole properties in transitional nuclei can be obtained in the interacting boson model-2 by F-spin breaking mechanism, which is associated with differences between the proton and neutron deformations. In particular, the long standing anomalies observed in the $g$-factors of the Os-Pt isotopes are resolved by a proper inclusion of F-spin breaking.
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arxiv:nucl-th/9408024
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The reaction $^{12}C(\nu_\mu,\mu^-) X$ has been measured near threshold using a $\pi ^+$ decay-in-flight $\nu_\mu$ beam from the Los Alamos Meson Physics Facility and a massive liquid scintillator neutrino detector (LSND). In the energy region $123.7 < E_\nu < 280$ MeV, the measured spectral shape is consistent with that expected from the Fermi Gas Model. However, the measured flux-averaged inclusive cross section ($(8.3 \pm 0.7 stat. \pm 1.6 syst.) \times 10^{-40} cm^2$) is more than a factor of 2 lower than that predicted by the Fermi Gas Model and by a recent random phase approximation calculation.
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arxiv:nucl-th/9410039
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A microscopic model for the $N\bar N\to\pi\pi$ process is presented in the meson exchange framework, which in the pseudophysical region agrees with available quasiempirical information. The scalar ($\sigma$) and vector ($\rho$) piece of correlated two--pion exchange in the pion--nucleon interaction is then derived via dispersion integrals over the unitarity cut. Inherent ambiguities in the method and implications for the description of pion--nucleon scattering data are discussed.
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arxiv:nucl-th/9411022
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The proton-proton bremsstrahlung is investigated within a coupled-channel model with the $\Delta$ degree of freedom. The model is consistent with the $NN$ scattering up to 1 GeV and the $\gamma N\Delta$ vertex determined in the study of pion photoproduction reactions. It is found that the $\Delta$ excitation can significantly improve the agreements with the $pp \rightarrow pp\gamma$ at $E_{lab}=280$ MeV. Predictions at $E_{lab}=550$ and $800$ MeV are presented for future experimental tests.
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arxiv:nucl-th/9412013
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Linear rate equations are used to describe the cascading decay of an initial heavy cluster into fragments. This representation is based upon a triangular matrix of transition rates. We expand the state vector of mass multiplicities, which describes the process, into the biorthonormal basis of eigenmodes provided by the triangular matrix. When the transition rates have a scaling property in terms of mass ratios at binary fragmentation vertices, we obtain solvable models with explicit mathematical properties for the eigenmodes. A suitable continuous limit provides an interpolation between the solvable models. It gives a general relationship between the decay products and the elementary transition rates.
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arxiv:nucl-th/9412026
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Rotation-induced time-odd components in the nuclear mean field are analyzed using the Hartree-Fock cranking approach with effective interactions SIII, SkM*, and SkP. Identical dynamical moments ${{\cal J}^{(2)}}$ are obtained for pairs of superdeformed bands $^{151}$Tb(2)--$^{152}$Dy(1) and $^{150}$Gd(2)--$^{151}$Tb(1). The corresponding relative alignments strongly depend on which time-odd mean-field terms are taken into account in the Hartree-Fock equations.
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arxiv:nucl-th/9502030
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We investigate the compression of nuclear matter in relativistic hydrodynamics. Nuclear matter is described by a $\sigma-\omega$--type model for the hadron matter phase and by the MIT bag model for the quark--gluon plasma, with a first order phase transition between both phases. In the presence of phase transitions, hydrodynamical solutions change qualitatively, for instance, one-dimensional stationary compression is no longer accomplished by a single shock but via a sequence of shock and compressional simple waves. We construct the analytical solution to the ``slab-on-slab'' collision problem over a range of incident velocities. The performance of numerical algorithms to solve relativistic hydrodynamics is then investigated for this particular test case. Consequences for the early compressional stage in heavy--ion collisions are pointed out.
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arxiv:nucl-th/9504021
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Through a sequence of large scale shell model calculations, total Gamow-Teller strengths ($S_+$ and $S_-$) in $^{54}$Fe and $^{56}$Fe are obtained. They reproduce the experimental values once the $\sigma\tau$ operator is quenched by the standard factor of $0.77$. Comparisons are made with recent Shell Model Monte Carlo calculations. Results are shown to depend critically on the interaction. From an analysis of the GT+ and GT$-$ strength functions it is concluded that experimental evidence is consistent with the $3(N-Z)$ sum rule.
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arxiv:nucl-th/9505007
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The differential cross-section of inelastic coherent diffractive dissociation off nuclei $p~+~^4$He $\rightarrow X ~+ ~^4$He is expressed in terms of the relative cumulants of the cross-section distribution $P_N(\sigma)$. The theoretical result for the ratio $r=\Bigg(\frac{d\sigma_{diff}}{dt}\Bigg)^{pHe}_{t=0} \Bigg/ \Bigg(\frac{d\sigma_{diff}}{dt}\Bigg)^{pp}_{t=0}=6.8 \div 7.6$ is close to the value $r=7.1 \pm 0.75$ which we extracted from the FNAL data. These are the only $A>2$ data of this kind. The comparison provides the first confirmation of the cross-section fluctuation approach to the description of the absolute value of the inelastic diffraction cross-section off nuclei. It provides also a new constraint on the first 4 cumulants of the cross-section distribution.
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arxiv:nucl-th/9506010
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The neutron direct radiative capture (DRC) process is investigated, highlighting the role of incident p-wave neutrons. A set of calculations is shown for the 12-C(n,gamma) process at incoming neutron energies up to 500 keV, a crucial region for astrophysics. The cross section for neutron capture leading to loosely bound s, p and d orbits of 13-C is well reproduced by the DRC model demonstrating the feasibility of using this reaction channel to study the properties of nuclear wave functions on and outside the nuclear surface. A sensitivity analysis of the results on the neutron-nucleus interaction is performed for incident s- as well as p-waves. It turned out that the DRC cross section for p-wave neutrons is insensitive to this interaction, contrary to the case of incident s-wave neutrons. PACS number(s): 25.40Lw,21.10Gv,23.40.Hc
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arxiv:nucl-th/9508018
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We propose to introduce a new stochastic process in molecular dynamics in order to improve the description of the nucleon emission process from a hot nucleus. We give momentum fluctuations originating from the momentum width of the nucleon wave packet to the nucleon stochastically when it is being emitted from the nucleus. We show by calculating the liquid gas phase equilibrium in the case of antisymmetrized molecular dynamics, that with this improvement, we can recover the quantum mechanical statistical property of the nucleus for the particle emission process.
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arxiv:nucl-th/9508025
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The transverse momentum dependence of Hanbury-Brown/Twiss (HBT) interferometry radii for 2-body correlation functions provides experimental access to the collective dynamics in heavy-ion collisions. We present an analytical approximation scheme for these HBT radii which combines the recently derived model-independent expressions with an approximate determination of the saddle point of the emission function. The method is illustrated for a longitudinally boost-invariant hydrodynamical model of a heavy ion collision with freeze-out on a sharp hypersurface. The analytical approximation converges rapidly to the width of the numerically computed correlation function and reproduces correctly its exact transverse momentum dependence. However, higher order corrections within our approximation scheme are essential, and the previously published lowest order results with simple $m_{\perp}$ scaling behaviour are quantitatively and qualitatively unreliable.
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arxiv:nucl-th/9508040
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We study the structure of nucleon pairs within a simple model consisting of a square well in three dimensions and a delta-function residual interaction between two weakly-bound particles at the Fermi surface. We include the continuum by enclosing the entire system in a large spherical box. To a good approximation, the continuum can be replaced by a small set of optimally-determined resonance states, suggesting that in many nuclei far from stability it may be possible to incorporate continuum effects within traditional shell-model based approximations.
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arxiv:nucl-th/9509028
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Properties of octupole vibrations in rapidly rotating nuclei are discussed. Microscopic RPA calculations based on the cranked shell model are performed to investigate the interplay between rotation and vibrations. The ability of this model to describe the properties of collective vibrations built on the ground bands in rare-earth and actinide nuclei is demonstrated at high angular momentum. The octupole vibrational states in even-even superdeformed Hg nuclei are also predicted and compared with available experimental data. A new interpretation of the observed excited superdeformed bands invoking these octupole bands is proposed.
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arxiv:nucl-th/9509043
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The Glauber method is extensively used to describe the motion of a hadronic projectile in interaction with the surrounding nuclear medium. One of the main approximations consists in the linearization of the wave equation for the interacting particle. We have studied the consequences of such an assumption in the case of the $^{12}\mathrm{C(e,e}'\mathrm{p)}^{11}\hbox{\rm B}^*$ reaction at high proton momenta by comparing the results with the predictions obtained when all the ingredients of the calculation are unchanged but the second-order differential equation for the scattered wave, which is solved exactly for each partial wave up to a maximum of 120 spherical harmonics. We find that the Glauber cross section is always larger by a factor $10 \div 20 \%$, even at vanishing missing momenta. We give a quantum-mechanical explanation of this discrepancy. Nevertheless, a good correlation is found between the two predictions as functions of the missing momentum, especially in parallel kinematics.
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arxiv:nucl-th/9509045
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The technique of dispersion integration over the mass of composite particle is used to describe the reaction of the deuteron photodisintegration. The influence of the final state interaction (FSI) on the total cross section, calculated with and without inelasticity is investigated. Numerical results depend on the choice of the vertex function for the isobar photoproduction.
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arxiv:nucl-th/9510008
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The hadronic phase space distributions calculated with the transport model RQMD for central S(200 AGeV) on S and Pb(160AGeV) on Pb collisions are analyzed to study the deviations from ideal hydrodynamical evolution. After the preequilibrium stage, which lasts for approximately 4 (2) fm/c in Pb+Pb (S+S) the source stays in approximate kinetic equilibrium for about 2 fm/c at a temperature close to 140 MeV. The interactions of mesons last until around 14 (5) fm/c during which time strong transverse flow is generated. The interactions in the hadronic resonance gas are not sufficiently strong to maintain ideal fluid expansion. While pions acquire average transverse fluid velocities around 0.47-0.58 c, heavier particles like protons and kaons cannot keep up with the pionic fluid, since their average velocities are smaller by about 20 to 30 \%. Although kinetic equilibrium breaks down in the final dilute stage of $AA$ collisions, the system resembles a thermal system at a temperature of 130 MeV, if the free streaming of hadrons after freeze-out is suppressed. This freeze-out temperature is consistent with estimates based on mean free paths and expansion rates in a thermal fireball but lower than values derived from fits to measured particle ratios and transverse momentum spectra. The processes in RQMD to which the differences can be attributed to are the non-ideal expansion of the hadronic matter and the absence of chemical equilibrium at freeze-out.
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arxiv:nucl-th/9510056
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The recent discovery of isotopes with Z=110--111 suggests evidence for (1) a monopole--monopole interaction that does not appear explicitly in Nilsson--Strutinsky mass systematics, and (2) a competition between $SU(2)$ and $SU(3)$ dynamical symmetries that has been predicted for this region. Our calculations suggest that these new isotopes are near spherical, and may represent a true island of superheavy nuclei, but shifted downward in neutron number by these new physical effects.
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arxiv:nucl-th/9511037
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We investigate the Equation of State (EOS) of classical systems having 300 and 512 particles confined in a box with periodic boundary conditions. We show that such a system, independently on the number of particles investigated, has a critical density of about 1/3 the ground state density and a critical temperature of about $2.5~ MeV$. The mass distribution at the critical point exhibits a power law with $\tau = 2.23$. Making use of the grand partition function of Fisher's droplet model, we obtain an analytical EOS around the critical point in good agreement with the one extracted from the numerical simulations.
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arxiv:nucl-th/9512019
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The pseudoscalar and pseudovector $\eta N$ coupling constants are calculated from an effective vertex associated with the $a_0(980)\pi N$ triangle diagram. The predicted values are in agreement with the ones concluded from fitting $\eta $ photoproduction amplitudes. In this context we stress the importance of the properties of the scalar meson octet for $\eta $ meson physics.
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arxiv:nucl-th/9601002
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We present the results for the electric dipole amplitude for $\gamma N \to \pi^0 N$ at threshold at the $O(p^2)$ level in SU$_f$(3) chiral perturbation theory. We find that the SU$_f$(3) results differ only slightly from the SU$_f$(2) results. At the $O(p^3)$ level one encounters new, unknown counterterms to fix which one is likely to need the threshold photoproduction data themselves, thus losing predictive power. We suggest, instead, that the {\it difference} between the proton and neutron $\pi^0$ photoproduction amplitudes may provide a test of the convergence properties of the $\chi$PT in the present context. We urge that the neutron's electric dipole amplitude be measured.
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arxiv:nucl-th/9601036
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Using the relativistic transport model (ART), we predict the energy dependence of the stopping power, maximum baryon and energy densities, the population of resonance matter as well as the strength of the transverse and radial flow for central Au+Au reactions at beam momentum from 2 to 12 GeV/c available at Brookhaven's AGS. The maximum baryon and energy densities are further compared to the predictions of relativistic hydrodynamics assuming the formation of shock waves. We also discuss the Fermi-Landau scaling of the pion multiplicity in these reactions.
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arxiv:nucl-th/9601041
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A two-parameter quantum algebra $U_{qp}({\rm u}_2)$ is briefly investigated in this paper. The basic ingredients of a model based on the $U_{qp}({\rm u}_2)$ symmetry, the $qp$-rotator model, are presented in detail. Some general tendencies arising from the application of this model to the description of rotational bands of various atomic nuclei are summarized.
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arxiv:nucl-th/9602015
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Non-equilibrium modifications of the nuclear equation of state are assessed in the framework of Extended Irreversible Thermodynamics. The expected size of the non-equilibrium corrections to quantities like the nuclear-matter incompressibility $K$ and the liquid-vapor critical temperature $T_c$ are compared to the uncertainties associated at present with the usual equilibrium values. The quantitative estimates are obtained in situations characterized by a stationary planar shear flow of realistic magnitude, or by a stationary temperature gradient.
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arxiv:nucl-th/9602017
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In this work we calculate neutron and proton energy gaps in neutron star matter, using the Bonn meson--exchange interactions and a model--space approach to the gap equation. This approach allows a consistent calculation of energy gaps and single particle energies with the model--space Brueckner--Hartree--Fock (MBHF) method, without double counting of two--particle correlations. Neutron energy gaps are calculated at zero and finite temperature. Proton energy gaps are calculated at beta equilibrium, and it is shown that the inclusion of muons has a significant effect. The results are compared with those of other works, and the implications for neutron star physics are briefly discussed.
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arxiv:nucl-th/9602020
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We describe the development of a theoretical description of the structure of finite nuclei based on a relativistic quark model of the structure of the bound nucleons which interact through the (self-consistent) exchange of scalar and vector mesons.
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arxiv:nucl-th/9602022
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