Showing papers in "Physical Review C in 2005"

Multiphase transport model for relativistic heavy ion collisions

Abstract: We describe in detail how the different components of a multiphase transport (AMPT) model that uses the heavy ion jet interaction generator (HIJING) for generating the initial conditions, Zhang's parton cascade (ZPC) for modeling partonic scatterings, the Lund string fragmentation model or a quark coalescence model for hadronization, and a relativistic transport (ART) model for treating hadronic scatterings are improved and combined to give a coherent description of the dynamics of relativistic heavy ion collisions. We also explain the way parameters in the model are determined and discuss the sensitivity of predicted results to physical input in the model. Comparisons of these results to experimental data, mainly from heavy ion collisions at the BNL Relativistic Heavy Ion Collider, are then made in order to extract information on the properties of the hot dense matter formed in these collisions.

How much do heavy quarks thermalize in a heavy ion collision

Abstract: We investigate the thermalization of charm quarks in high-energy heavy-ion collisions. To this end, we calculate the diffusion coefficient in the perturbative quark gluon plasma and relate it to collisional energy loss and momentum broadening. We then use these transport properties to formulate a Langevin model for the evolution of the heavy quark spectrum in the hot medium. The model is strictly valid in the nonrelativistic limit and for all velocities $\ensuremath{\gamma}vl\ensuremath{\alpha}{s}^{\ensuremath{-}1/2}$ to leading logarithm in $T/{m}_{D}$. The corresponding Fokker-Planck equation can be solved analytically for a Bjorken expansion and the solution gives a simple estimate for the medium modifications of the heavy quark spectrum as a function of the diffusion coefficient. Finally we solve the Langevin equations numerically in a hydrodynamic simulation of the heavy-ion reaction. The results of this simulation are the medium modifications of the charm spectrum ${R}_{\mathit{AA}}$ and the expected elliptic flow ${v}_{2}({p}_{T})$ as a function of the diffusion coefficient.

New relativistic mean-field interaction with density-dependent meson-nucleon couplings

Abstract: We adjust a new improved relativistic mean-field effective interaction with explicit density dependence of the meson-nucleon couplings. The effective interaction DD-ME2 is tested in relativistic Hartree-Bogoliubov and quasiparticle random-phase approximation (QRPA) calculations of nuclear ground states and properties of excited states, in calculation of masses, and it is applied to the analysis of very recent data on superheavy nuclei.

Electron energy spectra, fluxes, and day-night asymmetries of 8B solar neutrinos from measurements with NaCl dissolved in the heavy-water detector at the Sudbury Neutrino Observatory

Abstract: Results are reported from the complete salt phase of the Sudbury Neutrino Observatory experiment in which NaCl was dissolved in the {sup 2}H{sub 2}O (''D{sub 2}O'') target. The addition of salt enhanced the signal from neutron capture as compared to the pure D{sub 2}O detector. By making a statistical separation of charged-current events from other types based on event-isotropy criteria, the effective electron recoil energy spectrum has been extracted. In units of 10{sup 6}cm{sup -2}s{sup -1}, the total flux of active-flavor neutrinos from {sup 8}B decay in the Sun is found to be 4.94{sub -0.21}{sup +0.21}(stat){sub -0.34}{sup +0.38}(syst) and the integral flux of electron neutrinos for an undistorted {sup 8}B spectrum is 1.68{sub -0.06}{sup +0.06}(stat){sub -0.09}{sup +0.08}(syst); the signal from ({nu}{sub x},e) elastic scattering is equivalent to an electron-neutrino flux of 2.35{sub -0.22}{sup +0.22}(stat){sub -0.15}{sup +0.15}(syst). These results are consistent with those expected for neutrino oscillations with the so-called large mixing angle parameters and also with an undistorted spectrum. A search for matter-enhancement effects in the Earth through a possible day-night asymmetry in the charged-current integral rate is consistent with no asymmetry. Including results from other experiments, the best-fit values for two-neutrino mixing parameters are {delta}m{sup 2}=(8.0{sub -0.4}{sup +0.6})x10{sup -5}more » eV{sup 2} and {theta}=33.9{sub -2.2}{sup +2.4} degrees.« less

Azimuthal anisotropy in Au+Au collisions at sNN=200GeV

Abstract: The results from the STAR Collaboration on directed flow (v(1)), elliptic flow (v(2)), and the fourth harmonic (v(4)) in the anisotropic azimuthal distribution of particles from Au+Au collisions at root s(NN) = 200 GeV are summarized and compared with results from other experiments and theoretical models. Results for identified particles are presented and fit with a blast-wave model. Different anisotropic flow analysis methods are compared and nonflow effects are extracted from the data. For v(2), scaling with the number of constituent quarks and parton coalescence are discussed. For v(4), scaling with v(2)(2) and quark coalescence are discussed.

Thermalization of gluons in ultrarelativistic heavy ion collisions by including three-body interactions in a parton cascade

Abstract: We develop a new 3 + 1 dimensional Monte Carlo cascade solving the kinetic on-shell Boltzmann equations for partons including the inelastic gg{r_reversible}ggg pQCD processes. The back reaction channel is treated - for the first time - fully consistently within this scheme. An extended stochastic method is used to solve the collision integral. The frame dependence and convergency are studied for a fixed tube with thermal initial conditions. The detailed numerical analysis shows that the stochastic method is fully covariant and that convergency is achieved more efficiently than within a standard geometrical formulation of the collision term, especially for high gluon interaction rates. The cascade is then applied to simulate parton evolution and to investigate thermalization of gluons for a central Au+Au collision at RHIC energy. For this study the initial conditions are assumed to be generated by independent minijets with p{sub T}>p{sub 0}=2 GeV. With that choice it is demonstrated that overall kinetic equilibration is driven mainly by the inelastic processes and is achieved on a scale of 1 fm/c. The further evolution of the expanding gluonic matter in the central region then shows almost an ideal hydrodynamical behavior. In addition, full chemical equilibration of the gluons follows onmore » a longer time scale of about 3 fm/c.« less

Renormalization of one-pion exchange and power counting

Abstract: The renormalization of the chiral nuclear interactions is studied. In leading order, the cutoff dependence is related to the singular tensor interaction of the one-pion exchange potential. In S waves and in higher partial waves where the tensor force is repulsive this cutoff dependence can be absorbed by counterterms expected at that order. In the other partial waves additional contact interactions are necessary. The implications of this finding for the effective field theory program in nuclear physics are discussed.

Proton elastic form-factor ratios to Q**2 = 3.5-GeV**2 by polarization transfer

Abstract: The ratio of the proton elastic electromagnetic form factors, GEp/GMp, was obtained by measuring Pt and P, the transverse and longitudinal recoil proton polarization components, respectively, for the elastic epepreaction in the four-momentum transfer squared range of 0.5 to 3.5 GeV2. In the single-photon exchange approximation, GEp/GMp is directly proportional to Pt/P. The simultaneous measurement of Pt and P in a polarimeter reduces systematic uncertainties. The results for GEp/GMp show a systematic decrease with increasing Q2, indicating for the first time a definite difference in the distribution of charge and magnetization in the proton. The data have been reanalyzed and their systematic uncertainties have become significantly smaller than those reported previously. (Less)

Measurement of the response of a Ga solar neutrino experiment to neutrinos from a {sup 37}Ar source

Abstract: An intense source of {sup 37}Ar was produced by the (n,{alpha}) reaction on {sup 40}Ca by irradiating 330 kg of calcium oxide in the fast neutron breeder reactor at Zarechny, Russia The {sup 37}Ar was released from the solid target by dissolution in acid, collected from this solution, purified, sealed into a small source, and brought to the Baksan Neutrino Observatory where it was used to irradiate 13 tonnes of gallium metal in the Russian-American gallium solar neutrino experiment SAGE Ten exposures of the gallium to the source, whose initial strength was 409{+-}2kCi, were carried out during the period April to September 2004 The {sup 71}Ge produced by the reaction {sup 71}Ga({nu}{sub e},e{sup -}){sup 71}Ge was extracted, purified, and counted The measured production rate was 110{sub -09}{sup +10} (stat){+-}06 (syst) atoms of {sup 71}Ge/d, which is 079{sub -010}{sup +009} of the theoretically calculated production rate When all neutrino source experiments with gallium are considered together, there is an indication the theoretical cross section has been overestimated

Pion interferometry in Au+Au collisions at √ sNN = 200 GeV

Abstract: We present a systematic analysis of two-pion interferometry in Au+Au collisions at {radical}(s{sub NN})=200 GeV using the STAR detector at Relativistic Heavy Ion Collider. We extract the Hanbury-Brown and Twiss radii and study their multiplicity, transverse momentum, and azimuthal angle dependence. The Gaussianness of the correlation function is studied. Estimates of the geometrical and dynamical structure of the freeze-out source are extracted by fits with blast-wave parametrizations. The expansion of the source and its relation with the initial energy density distribution is studied.

Nucleon-nucleon cross sections in neutron-rich matter and isospin transport in heavy-ion reactions at intermediate energies

Abstract: Nucleon-nucleon (NN) cross sections are evaluated in neutron-rich matter using a scaling model according to density, momentum, and isospin dependent nucleon effective masses. It is found that the in-medium NN cross sections are not only reduced but also have a different isospin dependence compared with the free-space ones. Because of the neutron-proton effective mass splitting the difference between nn and pp scattering cross sections increases with the increasing isospin asymmetry of the medium. Within the transport model IBUU04, the in-medium NN cross sections are found to influence significantly the isospin transport in heavy-ion reactions. With the in-medium NN cross sections, a symmetry energy of ${E}_{\mathrm{sym}}(\ensuremath{\rho})\ensuremath{\approx}31.6(\ensuremath{\rho}/{\ensuremath{\rho}}_{0}){}^{0.69}$ was found most acceptable compared with both the MSU isospin diffusion data and the presently acceptable neutron-skin thickness in $^{208}\mathrm{Pb}$. The isospin dependent part ${K}_{\mathrm{asy}}({\ensuremath{\rho}}_{0})$ of isobaric nuclear incompressibility was further narrowed down to $\ensuremath{-}500\ifmmode\pm\else\textpm\fi{}50$ MeV. The possibility of determining simultaneously the in-medium NN cross sections and the symmetry energy was also studied. The proton transverse flow, or even better the combined transverse flow of neutrons and protons, can be used as a probe of the in-medium NN cross sections without much hindrance from the uncertainties of the symmetry energy.

Systematics of nuclear level density parameters

Abstract: The level density parameters for backshifted Fermi gas (both without and with energy-dependent level density parameter) and constant-temperature models have been determined for 310 nuclei between $^{18}\mathrm{F}$ and $^{251}\mathrm{Cf}$ by fitting of the complete level schemes at low excitation energies and s-wave neutron resonance spacings at the neutron binding energies. Simple formulas are proposed for the description of the two parameters of each of these models, which involve only quantities available from the mass tables. These formulas may constitute a reliable tool for extrapolating to nuclei far from stability, where nuclear level densities cannot be measured.

Thermalization of heavy quarks in the quark-gluon plasma

Abstract: Charm- and bottom-quark rescattering in a quark-gluon plasma (QGP) is investigated with the objective of assessing the approach toward thermalization. Employing a Fokker-Planck equation to approximate the collision integral of the Boltzmann equation we augment earlier studies based on perturbative parton cross sections by introducing resonant heavy-light quark interactions. The latter are motivated by recent QCD lattice calculations that indicate the presence of ``hadronic'' states in the QGP. We model these states by colorless (pseudo-) scalar and (axial-) vector D and B mesons within a heavy-quark effective theory framework. We find that the presence of these resonances at moderate QGP temperatures substantially accelerates the kinetic equilibration of c quarks as compared to using perturbative interactions. We also comment on consequences for D-meson observables in ultrarelativistic heavy-ion collisions.

Systematic studies of the centrality and √sNN dependence of the dET/dη and dNch/dη in heavy ion collisions at midrapidity

Abstract: The PHENIX experiment at the relativistic heavy ion collider (RHIC) has measured transverse energy and charged particle multiplicity at midrapidity in $\mathrm{Au}+\mathrm{Au}$ collisions at center-of-mass energies $\sqrt{{s}_{\mathrm{NN}}}=19.6,130$, and $200\phantom{\rule{0.3em}{0ex}}\text{GeV}$ as a function of centrality. The presented results are compared to measurements from other RHIC experiments and experiments at lower energies. The $\sqrt{{s}_{\mathrm{NN}}}$ dependence of $dE{}_{T}/d\ensuremath{\eta}$ and $dN{}_{\mathrm{ch}}/d\ensuremath{\eta}$ per pair of participants is consistent with logarithmic scaling for the most central events. The centrality dependence of $dE{}_{T}/d\ensuremath{\eta}$ and $dN{}_{\mathrm{ch}}/d\ensuremath{\eta}$ is similar at all measured incident energies. At RHIC energies, the ratio of transverse energy per charged particle was found to be independent of centrality and growing slowly with $\sqrt{{s}_{\mathrm{NN}}}$. A survey of comparisons between the data and available theoretical models is also presented.

Nuclear matter symmetry energy and the neutron skin thickness of heavy nuclei

Abstract: Correlations between the thickness of the neutron skin in finite nuclei and the nuclear matter symmetry energy are studied in the Skyrme Hartree-Fock model. From the most recent analysis of the isospin diffusion data in heavy-ion collisions based on an isospin- and momentum-dependent transport model with in-medium nucleon-nucleon cross sections, a value of $L=88\ifmmode\pm\else\textpm\fi{}25$ MeV for the slope of the nuclear symmetry energy at saturation density is extracted, and this imposes stringent constraints on both the parameters in the Skyrme effective interactions and the neutron skin thickness of heavy nuclei. Predicted thickness of the neutron skin is $0.22\ifmmode\pm\else\textpm\fi{}0.04$ fm for $^{208}\mathrm{Pb}$, $0.29\ifmmode\pm\else\textpm\fi{}0.04$ fm for $^{132}\mathrm{Sn}$, and $0.22\ifmmode\pm\else\textpm\fi{}0.04$ fm for $^{124}\mathrm{Sn}$.

Microscopic approach of fission dynamics applied to fragment kinetic energy and mass distributions in U 238

Abstract: The collective dynamics of low-energy fission in $^{238}\mathrm{U}$ is described within a time-dependent formalism based on the Gaussian overlap approximation of the time-dependent generator coordinate method. The intrinsic deformed configurations of the nucleus are determined from the self-consistent Hartree-Fock-Bogoliubov procedure employing the effective force D1S with constraints on the quadrupole and octupole moments. Fragment kinetic energy and mass distributions are calculated and compared with experimental evaluations. The effect of the collective dynamics along the fission paths and the influence of initial conditions on these distributions are analyzed and discussed.

Energy loss of leading partons in a thermal QCD medium

Abstract: We consider bremsstrahlung energy loss for hard partons traversing a quark-gluon plasma (QCP). Accounting correctly for the probabilistic nature of the energy loss, and making a leading-order-accurate treatment of bremsstrahlung, we find that the suppression of the spectrum is nearly flat, with the most suppression at energies $E~30\phantom{\rule{0.3em}{0ex}}T$ (where T is the QGP temperature), without the need for initial state effects such as shadowing and the Cronin effect. This flat pattern should also be observed at the LHC (Large Hadron Collider) out to an energy of $~30\phantom{\rule{0.3em}{0ex}}\mathrm{GeV}$.

Energy loss of charm quarks in the quark-gluon plasma: Collisional vs radiative losses

Abstract: In considering the collisional energy loss rates of heavy quarks from hard light parton interactions, we computed the total energy loss of a charm quark for a static medium. For the energy range $E~5$--10 GeV of charm quark, it proved to be almost the same order as that of radiative ones estimated to a first-order opacity expansion. The collisional energy loss becomes much more important for lower energy charm quarks, and this feature could be very interesting for the phenomenology of hadrons spectra. Using such collisional energy loss rates, we estimate the momentum loss distribution employing a Fokker-Planck equation and the total energy loss of a charm quark for an expanding quark-gluon plasma under conditions resembling the energies presently available at the BNL Relativistic Heavy Ion Collider. The fractional collisional energy loss is found to be suppressed by a factor of 5 as compared to the static case and does not depend linearly on the system size. We also investigate the heavy to light hadrons $D/\ensuremath{\pi}$ ratio at moderately large (5--10 GeV/c) transverse momenta and comment on its enhancement.

Energy loss of leading hadrons and direct photon production in evolving quark-gluon plasma

Abstract: We calculate the nuclear modification factor of neutral pions and the photon yield at high ${p}_{T}$ in central Au-Au collisions at the Relativistic Heavy-Ion Collider (RHIC) ($\sqrt{s}=200\phantom{\rule{03em}{0ex}}\text{GeV}$) and Pb-Pb collisions at the Large Hadron Collider (LHC) ($\sqrt{s}=5500\phantom{\rule{03em}{0ex}}\text{GeV}$) A leading-order accurate treatment of jet energy loss in the medium has been convolved with a physical description of the initial spatial distribution of jets and a one dimensional hydrodynamic expansion We reproduce the nuclear modification factor for pions ${R}_{\mathit{AA}}$ at RHIC, assuming an initial temperature ${T}_{i}=370\phantom{\rule{03em}{0ex}}\text{MeV}$ and a formation time ${\ensuremath{\tau}}_{i}=026$ fm/c, corresponding to $\mathit{dN}/\mathit{dy}=1260$ The resulting suppression depends on the particle rapidity density $\mathit{dN}/\mathit{dy}$ but weakly on the initial temperature The jet energy loss treatment is also included in the calculation of high ${p}_{T}$ photons Photons coming from primordial hard N-N scattering are the dominant contribution at RHIC for ${p}_{T}g5\phantom{\rule{03em}{0ex}}\text{GeV}$, whereas at the LHC, the range $8l{p}_{T}l14\phantom{\rule{03em}{0ex}}\text{GeV}$ is dominated by jet-photon conversion in the plasma

α-nucleus potential for α-decay and sub-barrier fusion

Abstract: The set of parameters for \ensuremath{\alpha}-nucleus potential is derived by using the data for both the \ensuremath{\alpha}-decay half-lives and the fusion cross sections around the barrier for reactions $\ensuremath{\alpha}+$$^{40}\mathrm{Ca}$, $\ensuremath{\alpha}+$$^{59}\mathrm{Co}$, and $\ensuremath{\alpha}+$$^{208}\mathrm{Pb}$. The \ensuremath{\alpha}-decay half-lives are obtained in the framework of a cluster model using the WKB approximation. The evaluated \ensuremath{\alpha}-decay half-lives and the fusion cross sections agreed well with the data. Fusion reactions between \ensuremath{\alpha} particles and heavy nuclei can be used for both the formation of very heavy nuclei and spectroscopic studies of the formed compound nuclei.

Onset of classical QCD dynamics in relativistic heavy ion collisions

Abstract: The experimental results on hadron production obtained recently at RHIC offer a new prospective on the energy dependence of the nuclear collision dynamics. In particular, it is possible that parton saturation---the phenomenon likely providing initial conditions for the multiparticle production at RHIC energies---may have started to set in central heavy ion collisions already around the highest CERN SPS energy. We examine this scenario, and make predictions based on high density QCD for the forthcoming $\sqrt{s}=22$ GeV run at RHIC.

Heavy quarkonia in quark-gluon plasma

Abstract: Using the color-singlet free energy ${F}_{1}$ and total internal energy ${U}_{1}$ obtained by Kaczmarek et al. (hep-lat/0309121) for a static quark Q and an antiquark $\overline{Q}$ in quenched QCD, we study the binding energies and wave functions of heavy quarkonia in a quark-gluon plasma. By minimizing the grand potential in a simplified schematic model, we find that the proper color-singlet $Q\text{\ensuremath{-}}\overline{Q}$ potential can be obtained from the total internal energy ${U}_{1}$ by subtracting the gluon internal energy contributions. We carry out this subtraction in the local energy-density approximation in which the gluon energy density can be related to the local gluon pressure by the quark-gluon plasma equation of state. We find in this approximation that the proper color-singlet $Q\text{\ensuremath{-}}\overline{Q}$ potential is approximately ${F}_{1}$ for $T~{T}_{c}$ and it changes to $\frac{3}{4}{F}_{1}+\frac{1}{4}{U}_{1}$ at high temperatures. In this potential model, the $J/\ensuremath{\psi}$ is weakly bound above the phase-transition temperature ${T}_{c}$, and it dissociates spontaneously above $1.62{T}_{c}$, whereas ${\ensuremath{\chi}}_{c}$ and ${\ensuremath{\psi}}^{'}$ are unbound in the quark-gluon plasma. The bottomium states $\ensuremath{\Upsilon},{\ensuremath{\chi}}_{b}$, and ${\ensuremath{\Upsilon}}^{'}$ are bound in the quark-gluon plasma and they dissociate at $4.1{T}_{c},1.18{T}_{c},$ and $1.38{T}_{c}$ respectively. For comparison, we evaluate the heavy quarkonium binding energies also in other models using the free energy ${F}_{1}$ or the total internal energy ${U}_{1}$ as the $Q\text{\ensuremath{-}}\overline{Q}$ potential. The comparison shows that the model with the new $Q\text{\ensuremath{-}}\overline{Q}$ potential proposed here gives dissociation temperatures that agree best with those from spectral function analyses. We evaluate the cross section for $\ensuremath{\sigma}(g+J/\ensuremath{\psi}\ensuremath{\rightarrow}c+\overline{c})$ and its inverse process to determine the $J/\ensuremath{\psi}$ dissociation width and the rate of $J/\ensuremath{\psi}$ production by recombining c and $\overline{c}$ in the quark-gluon plasma.

Centrality and pseudorapidity dependence of elliptic flow for charged hadrons in Au+Au collisions at √snn = 200 geV

Abstract: This Rapid Communication describes the measurement of elliptic flow for charged particles in Au+Au collisions at {radical}(s{sub NN})=200 GeV using the PHOBOS detector at the Relativistic Heavy Ion Collider. The measured azimuthal anisotropy is presented over a wide range of pseudorapidity for three broad collision centrality classes for the first time at this energy. Two distinct methods of extracting the flow signal were used to reduce systematic uncertainties. The elliptic flow falls sharply with increasing |{eta}| at 200 GeV for all the centralities studied, as observed for minimum-bias collisions at {radical}(s{sub NN})=130 GeV.

Jülich hyperon-nucleon model revisited

Abstract: A one-boson-exchange model for the hyperon-nucleon (\Lambda N, \Sigma N) interaction is presented. The model incorporates the standard one boson exchanges of the lowest pseudoscalar and vector meson multiplets with coupling constants fixed by SU(6) flavor symmetry relations. As the main new feature of the model, the contributions in the scalar--isoscalar (\sigma) and vector--isovector (\rho) exchange channels are now constrained by a microscopic model of correlated \pi\pi and K \bar K exchange. Additional short-ranged ingredients of the model in the scalar--isovector (a_0) and scalar--isospin-1/2 (\kappa) channels are likewise viewed as arising from meson-meson correlations but are treated phenomenologically. With this model a satisfactory reproduction of the available hyperon-nucleon data can be achieved.

Synthesis of elements 115 and 113 in the reaction 243 Am + 48 Ca

Abstract: The results of two experiments designed to synthesize element 115 isotopes in the {sup 243}Am+{sup 48}Ca reaction are presented. Two new elements with atomic numbers 113 and 115 were observed for the first time. With 248-MeV {sup 48}Ca projectiles, we observed three similar decay chains consisting of five consecutive {alpha} decays, all detected in a total time interval of 30 s. Each chain was terminated by a spontaneous fission (SF) with a high-energy release and a lifetime of about a day. With 253-MeV {sup 48}Ca projectiles, we registered a different decay chain of consecutive {alpha} decays detected in a time interval of 0.5 s, also terminated by spontaneous fission, but after 1.8 h. The decay properties of the eleven new {alpha}- and SF-decaying nuclei are consistent with expectations for consecutive {alpha} decays originating from the parent isotopes {sup 288}115 and {sup 287}115, produced in the 3n- and 4n-evaporation channels, respectively. Support for the assignment of the atomic numbers of all of the nuclei in the {sup 288}115 decay chain was obtained in an independent experiment in which a long-lived spontaneous fission activity, {sup 268}Db (15 events), was found to be chemically consistent with the fifth group of the periodic table.more » The odd-odd isotope {sup 288}115 was observed with largest cross section of about 4 pb. In the SF decay of {sup 268}Db, a total kinetic energy of 230 MeV and a neutron multiplicity per fission of 4.2 were measured. The decay properties of the 11 new isotopes with Z=105-115 and the production cross sections are in agreement with modern concepts of the role of nuclear shells in the stability of superheavy nuclei. The experiments were carried out at the Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research.« less

Determination of the parameters of a Skyrme type effective interaction using the simulated annealing approach

Abstract: We implement for the first time the simulated annealing method to the problem of searching for the global minimum in the hypersurface of the ${\ensuremath{\chi}}^{2}$ function, which depends on the values of the parameters of a Skyrme-type effective nucleon-nucleon interaction. We undertake a realistic case of fitting the values of the Skyrme parameters to an extensive set of experimental data on the ground-state properties of many nuclei, ranging from normal to exotic ones. The set of experimental data used in our fitting procedure includes the radii for the valence $1{d}_{5/2}$ and $1{f}_{7/2}$ neutron orbits in the $^{17}\mathrm{O}$ and $^{41}\mathrm{Ca}$ nuclei, respectively, and the breathing-mode energies for several nuclei, in addition to the typically used data on binding energy, charge radii, and spin-orbit splitting. We also include in the fit the critical density ${\ensuremath{\rho}}_{\mathrm{cr}}$ and further constrain the values of the Skyrme parameters by requiring that (i) the quantity $P=3\ensuremath{\rho}(\mathit{dS}/d\ensuremath{\rho})$, directly related to the slope of the symmetry energy S, must be positive for densities up to $3{\ensuremath{\rho}}_{0}$; (ii) the enhancement factor \ensuremath{\kappa}, associated with the isovector giant dipole resonance, should lie in the range of 0.1--0.5; and (iii) the Landau parameter ${G}_{0}^{'}$ is positive at $\ensuremath{\rho}={\ensuremath{\rho}}_{0}$. We provide simple but consistent schemes to account for the center-of-mass corrections to the binding energy and charge radii.

Fusion by diffusion. II. Synthesis of transfermium elements in cold fusion reactions

Abstract: We describe a method of estimating cross sections for the synthesis of very heavy nuclei by the fusion of two lighter ones. The cross section is considered to be the product of three factors: the cross section for the projectile to overcome the Coulomb barrier, the probability that the resulting composite nucleus reaches the compound nucleus configuration by a shape fluctuation treated as a diffusion of probability in one dimension, and the probability that the excited compound nucleus survives fission. Semi-empirical formulas for the mean Coulomb barrier height and its distribution around the mean are constructed. After overcoming the Coulomb barrier the system is assumed to be injected into an ``asymmetric fission valley'' by a rapid growth of the neck between the target and projectile at approximately frozen asymmetry and elongation. Diffusion in the elongation coordinate in this valley can occasionally bring the system over the saddle separating the injection point from the compound nucleus configuration. This is the stage that accounts for the hindrance to fusion observed for very heavy reacting systems. The competition between deexcitation of the compound nucleus by neutron emission and fission is treated by standard methods, but an interesting insight allows one to predict in an elementary way the location of the maximum in the resulting excitation function. Adjusting one parameter in the theory causes the calculated peak cross sections to agree within about a factor of 2 or so with 12 measured or estimated values for ``cold'' one-neutron-out reactions where targets of $^{208}\mathrm{Pb}$ and $^{209}\mathrm{Bi}$ are bombarded with projectiles ranging from $^{48}\mathrm{Ca}$ to $^{70}\mathrm{Zn}$. The centroids of the excitation functions agree with theory to within 1 or 2 MeV for the six cases where they have been determined, and their widths are reproduced. ``Hot'' fusion reactions, where several neutrons are emitted, are not treated, except that a comparison is made between the hindrance factors in cold and hot reactions to make elements with atomic numbers 112 to 118. The calculated diffusive hindrances in the hot reactions are less unfavorable by 4 to 5 orders of magnitude.

Relativistic model for nuclear matter and atomic nuclei with momentum-dependent self-energies

Abstract: The Lagrangian density of standard relativistic mean-field models with density-dependent meson-nucleon coupling vertices is modified by introducing couplings of the meson fields to derivative nucleon densities. As a consequence, the nucleon self-energies that describe the effective in-medium interaction become momentum dependent. In this approach it is possible to increase the effective (Landau) mass of the nucleons, that is related to the density of states at the Fermi energy, as compared to conventional relativistic models. At the same time the relativistic effective (Dirac) mass is kept small to obtain a realistic strength of the spin-orbit interaction. Additionally, the empirical Schr\"odinger-equivalent central optical potential from Dirac phenomenology is reasonably well described. A parametrization of the model is obtained by a fit to properties of doubly magic atomic nuclei. Results for symmetric nuclear matter, neutron matter, and finite nuclei are discussed.

Momentum-space treatment of the Coulomb interaction in three-nucleon reactions with two protons

Abstract: The Coulomb interaction between two protons is included in the calculation of proton-deuteron elastic scattering, radiative proton-deuteron capture, and two-body electromagnetic disintegration of $^{3}\mathrm{He}$. The hadron dynamics is based on the purely nucleonic charge-dependent (CD) Bonn potential and its realistic extension CD Bonn $+\phantom{\rule{0.3em}{0ex}}\ensuremath{\Delta}$ to a coupled-channel two-baryon potential, allowing for single virtual $\ensuremath{\Delta}$-isobar excitation. Calculations are done using integral equations in momentum space. The screening and renormalization approach is employed for including the Coulomb interaction. Convergence of the procedure is found at moderate screening radii. The reliability of the method is demonstrated. The Coulomb effect on observables is seen at low energies for the entire kinematic regime. In proton-deuteron elastic scattering at higher energies the Coulomb effect is confined to forward scattering angles; the $\ensuremath{\Delta}$-isobar effect found previously remains unchanged by the Coulomb effect. In electromagnetic reactions the Coulomb effect competes with other effects in a complicated way.

K(892)(*) resonance production in Au+Au and p+p collisions at root s(NN)=200 GeV

Abstract: The short-lived K(892)* resonance provides an efficient tool to probe properties of the hot and dense medium produced in relativistic heavy-ion collisions. We report measurements of K* in {radical}(s{sub NN})=200 GeV Au+Au and p+p collisions reconstructed via its hadronic decay channels K(892)*{sup 0}{yields}K{pi} and K(892)*{sup {+-}}{yields}K{sub S}{sup 0}{pi}{sup {+-}} using the STAR detector at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory. The K*{sup 0} mass has been studied as a function of p{sub T} in minimum bias p+p and central Au+Au collisions. The K* p{sub T} spectra for minimum bias p+p interactions and for Au+Au collisions in different centralities are presented. The K*/K yield ratios for all centralities in Au+Au collisions are found to be significantly lower than the ratio in minimum bias p+p collisions, indicating the importance of hadronic interactions between chemical and kinetic freeze-outs. A significant nonzero K*{sup 0} elliptic flow (v{sub 2}) is observed in Au+Au collisions and is compared to the K{sub S}{sup 0} and {lambda} v{sub 2}. The nuclear modification factor of K* at intermediate p{sub T} is similar to that of K{sub S}{sup 0} but different from {lambda}. This establishes a baryon-meson effect over a mass effect in the particle production atmore » intermediate p{sub T} (2