Single-particle potential in a chiral approach to nuclear matter including short-range NN-terms

We extend a recent chiral approach to nuclear matter of Lutz et al.Phys. Lett. B 474, 7 (2000)) by calculating the underlying (complex-valued) single-particle potential U(p, k _f) + iW(p, k _f). The potential for a nucleon at the bottom of the Fermi sea, U(0, k _f0) = - 20.0 MeV, comes out as much too weakly attractive in this approach. Even more seriously, the total single-particle energy does not rise monotonically with the nucleon momentum p, implying a negative effective nucleon mass at the Fermi surface. Also, the imaginary single-particle potential, W(0, k _f0) = 51.1 MeV, is too large. More realistic single-particle properties together with a good nuclear-matter equation of state can be obtained if the short-range contributions of non-pionic origin are treated in mean-field approximation (i.e. if they are not further iterated with 1π-exchange). We also consider the equation of state of pure neutron matter ˉE_n(k _n) and the asymmetry energy A(k _f) in that approach. The downward bending of these quantities above nuclear-matter saturation density seems to be a generic feature of perturbative chiral pion-nucleon dynamics. Received: 19 December 2002 / Accepted: 11 February 2003 / Published online: 15 April 2003     

Isospin properties of () reactions for the formation of deeply-bound antikaonic nuclei

The formation of deeply-bound antikaonic nuclear states in nuclear (K⁻,N) reactions is investigated theoretically within a distorted-wave impulse approximation (DWIA), considering the isospin properties of the Fermi-averaged elementary amplitudes. We calculate the formation cross sections of the deeply-bound states by the (K⁻,N) reactions on the nuclear targets, ¹²C and ²⁸Si, at incident K⁻ lab momentum p_K⁻=1.0 GeV/c and θ_lab=0°, introducing a complex effective nucleon number N_eff for unstable bound states in the DWIA. The results show that the deeply-bound states can be populated dominantly by the (K⁻,n) reaction via the total isoscalar ΔT=0 transition owing to the isospin nature of the amplitudes, and that the cross sections described by ReN_eff and ArgN_eff enable to deduce the structure of the nuclear states; the calculated inclusive nucleon spectra for a deep -nucleus potential do not show distinct peak structure in the bound region. The few-body and states formed in (K⁻,N) reactions on s-shell nuclear targets, ³He, ³H and ⁴He, are also discussed.     

Neutron Matter Properties Using Skyrme Interaction

The purpose of the present work is to extend earlier nuclear matter calculations to study the properties of neutron matter. The binding energy per particle, symmetry energy, single particle potential, effective mass, and magnetic susceptibility are calculated using a modified Skyrme interaction. These are calculated as a function of the Fermi momentum k_f in the range 0 < k_f < 2 fm^?1. Two sets of the interaction parameters are obtained by fitting the interaction parameters using the available information on neutron matter. Relativistic corrections to the order 1/c² are also calculated. The relativistic corrections are very small and they increase as k_f is increased.     

Resonances in at rest

Data on at rest show two resonant processes: (a) f₀(1370)η,f₀(1370)→σσ and ρρ, (b) η(1440)σ, η(1440)→ηπ⁺π⁻. The branching ratio BR[f₀(1370)→ρρ]/BR[f₀(1370)→σσ]=0.98±0.25 in the mass range available here. Using data on , the ratio Γ_4π/Γ_2π5 for f₀(1370). The effects of the strongly s-dependent width of f₀(1370) are discussed in some detail.The η(1440) is observed decaying to ησ and a₀(980)π, with strong destructive interference between them. In its decay to a₀(980)π, a narrow peak appears in the ηπ mass spectrum, but 30–50 MeV above that usually attributed to a₀(980) and significantly above the KK threshold. This effect is explained naturally by a two-step process: η(1440)→K^*(890)K followed by rescattering of the two kaons through a₀(980) to ηπ above the KK threshold.     

Variational calculations of asymmetric nuclear matter

We report on variational calculations of the energy E(ρ, β) of asymmetric nuclear matter having ? = ?_n + ?_p = 0.05 to 0.35 fm^?3, and β = (?_n ? ?_p/g9 = 0 to 1. The nuclear h used in this work consists of a realistic two-nucleon interaction, called v₁₄, that fits the available nucleon-nucleon scattering data up to 425 MeV, and a phenomenological three nucleon interaction adjusted to reproduce the empirical properties of symmetric nuclear matter. The variational many-body theory of symmetric nuclear matter is extended to treat matter with neutron excess. Numerical and analytic studies of the β-dependence of various contributions to the nuclear matter energy show that at ? < 0.35 fm^?3 the β⁴ terms are very small, and that the interaction energy EI(ρ, β) defined as E(ρ, β) ? T_F(ρ, β), where T_F is the Fermi-gas energy, is well approximated by EI₀(?) + β²EI₂(ρ). The calculated symmetry energy at equilibrium density is 30 MeV and it increases from 15 to 38 MeV as ? increases from 0.05 to 0.35 fm^?3.     

Bd,s– mass-differences from QCD spectral sum rules

We present the first QCD spectral sum rules analysis of the SU(3) breaking parameter ξ and an improved estimate of the renormalization group invariant (RGI) bag constant both entering into the B⁰_d,s– mass-differences. The averages of the results from the Laplace and moment sum rules to order α_s are and

Full-size image

, in units where f_π=130.7 MeV. Combined with the experimental data on the mass-differences ΔM_d,s, one obtains the constraint on the CKM weak mixing angle |V_ts/V_td|²20.0(1.1). Alternatively, using the weak mixing angle from the analysis of the unitarity triangle and the data on ΔM_d, one predicts ΔM_s=18.6(2.2) ps⁻¹ in agreement with the present experimental lower bound and within the reach of Tevatron 2.     

Vicinal Fluorine–Proton Coupling Constants: II. Individual Substituent Effects

The angular dependence and the effect of individual substituents upon the NMR vicinal fluorine–proton couplings3JFHhave been studied using data sets of experimental and calculated couplings. Coupling constants for a series of fluoroethane derivatives, CHXF–CH3and CH2F–CH2X(X= CH3, NH2, OH, and F), were calculated by means of the SCFab initioand semiempirical INDO/FPT methods. The calculated couplings reproduce correctly the main experimental trends in spite of the limitation in the calculation because of lack of electronic correlation and the use of medium size basis set. The individual substituent effects ΔKXiniare described by quadratic expressions on the relative electronegativities of substituents ΔχXi(ΔKXini=k0ni+kniΔχXi+ kniiΔχ2Xi). A selected data set of 58 experimental couplings, ranging from 1.9 to 44.4 Hz, has been collected from the literature. An extended Karplus equation with 16 coefficients that includes the electronegativity substituent effects has been derived from the experimental data set with a root-mean-square deviation of 1.2 Hz.     

Study of in flight

An analysis of data on is presented at beam momenta 600 to 1940 MeV/c. There is evidence for an I=1, J^PC=2⁻⁺ resonance in ηηπ⁰ with mass M=1880±20 MeV and width 255±45 MeV, decaying strongly to a₂(1320)η; it is too strong to be explained as the high mass tail of π₂(1670)→a₂(1320)η. There is tentative evidence also for weak decays to f₀(1500)π. It makes a natural partner to the η₂(1860).     

Modelling the quark propagator

We are interested in developing covariant, confining, and asymptotically free models of hadrons. With this goal in mind we have carried out a study of dynamical chiral symmetry breaking without imposing the frequently used approximation α_s(−(p−k)²) α₅(−p_>²), where p_>² ≡ max(p², k²) for the running coupling constant in the quark Schwinger-Dyson equation. We present numerical results in Landau gauge and compare these with earlier results obtained when using this approximation. We see in this context that a gluon propagator which has the form 1/q⁴ in the infrared is too singular and must be regulated. We derive a suitably generalized expression for the pion decay constant f_π. With essentially one free parameter we are able to reproduce reasonable results for various physical quantities of interest including , and Λ_QCD.     

Inclusive production of the meson in hadronic decays of the Z boson

The inclusive production rate of the ρ^±(770) vector meson in hadronic Z decays is measured with the ALEPH detector at the LEP collider. A total of 3.2 million hadronic events are selected from data recorded between 1991 and 1995. Decays of ρ^±→π⁰+π^± are reconstructed for x_E>0.05 and x_p>0.05 where x_p=p_ρ/p_beam and x_E=E_ρ/E_beam. The average ρ^± multiplicity per hadronic event is evaluated to be N(ρ^±)=2.59±0.03±0.15±0.04 where the first error is statistical and the second systematic. The third error is from the uncertainty in the extrapolation to x_p=x_E=0. The rates and differential cross-section are compared with Monte Carlo model predictions and OPAL measurements. Residual Bose–Einstein correlations are found to be an important component in the analysis.     

Λ spin–orbit splitting in heavy hypernuclei as deduced from DWIA analyses of the reaction

By taking nuclear core excitations into account, detailed structure calculations of ⁸⁹ _ΛY have been performed as a function of the Λ spin–orbit splitting. The obtained wave functions have been used to estimate the (π⁺,K⁺) reaction cross sections within the distorted-wave impulse approximation (DWIA). A theoretical explanation is given quantitatively for the first time of how to understand the doublet substructure of each major peak observed in medium-heavy hypernuclear production. A small Λ spin–orbit splitting of around δ(0f^Λ)=0.2 MeV is deduced, a value consistent with the small ΛN two-body spin–orbit interactions deduced from γ-ray measurements in three light hypernuclei.     

Physical properties of hot,dense matter: The general case

The thermodynamic properties of hot, dense matter are examined in the density range 10^?5 fm^?3 ? n ? 0.35 fm^?3 and the temperature range 0 ? T ? 21 MeV, for fixed lepton fractions Y_? = 0.4, 0.3 and 0.2 and for matter in β-equilibrium with no neutrinos. Three phases of the matter are considered: the nuclei phase is assumed to consist of Wigner-Seitz cells with central nuclei surrounded by a nucleon vapor containing also α-particles; in the bubbles phase the cell contains a central spherical bubble of nucleon vapor surrounded by dense nuclear matter; the third phase is that of uniform nuclear matter. All are immersed in a sea of leptons (electrons and neutrinos) and photons. The nuclei and bubbles are described by a compressible liquid drop model which is self-consistent in the sense that all of the constituent properties — bulk, surface, Coulomb energies and other minor contributions — are calculated from the same nuclear effective hamiltonian, in this case the Skyrme 1' interaction. The temperature dependence of all of these energies is included, for bulk and surface energies by direct calculation, for the Coulomb energy by combining in a plausible way the usual electrostatic energy and the numerical results pertaining to a hot Coulomb plasma. Lattice contributions to the Coulomb energy are an essential ingredient, and lattice modifications to the nuclear translational energy are included. A term is constructed to allow also for the reduced density of excited states of light nuclei. All of these modifications incorporate necessary physical effects which modify significantly the matter properties in some regions.     

Photoproduction of D mesons associated with a leading neutron

The photoproduction of D^*±(2010) mesons associated with a leading neutron has been observed with the ZEUS detector in ep collisions at HERA using an integrated luminosity of 80 pb⁻¹. The neutron carries a large fraction, x_L>0.2, of the incoming proton beam energy and is detected at very small production angles, θ_n<0.8 mrad, an indication of peripheral scattering. The D^* meson is centrally produced with pseudorapidity |η|<1.5, and has a transverse momentum p_T>1.9 GeV, which is large compared to the average transverse momentum of the neutron of 0.22 GeV. The ratio of neutron-tagged to inclusive D^* production is 8.85±0.93(stat.)^+0.48_−0.61(syst.)% in the photon–proton center-of-mass energy range 130<W<280 GeV. The data suggest that the presence of a hard scale enhances the fraction of events with a leading neutron in the final state.     

Speeds of sound and isentropic compressibilities of (2-ethoxyethanol + ethylene glycol, diethylene glycol, triethylene glycol, and tetraethylene glycol) binary mixtures at 298.15 K

The speed of sound (u) has been obtained at a frequency of 8.3 MHz in {CH₃CH₂OCH₂CH₂OH + HOCH₂CH₂(OCH₂CH₂)_nOH}for n = 0, 1, 2, and 3 over the whole composition range of studied binary liquid mixtures, at T = 298.15 K. The speed of sound values were combined with those of our previous results for densities and viscosities to obtain isentropic compressibility (κ_s), free volume (V_f), and intermolecular free length (L_f). From all these data excess isentropic compressibility (κ_s^E), excess free volume (V_f^E) and excess intermolecular free length (L_f^E) as well as the deviations of the speed of sound (Δu) were obtained. The results are interpreted in terms of molecular interactions occurring in the solutions.     

Analysis of inelastic scattering processes of electrons by localized electrons in quantum dots

The inelastic Coulomb scattering rate 1/τ_in of conduction electrons has been theoretically evaluated in the presence of localized states such as quantum dots. By a diagrammatical method, we have formulated 1/τ_in and its relation to the conductivity σ_loc(ω) through localized states. The dependence of τ_in on temperature T is examined in the case that σ_loc(ω) follows the Mott's model. It is found that 1/τ_in varies as T²(ln Δ/T)^d+1 where d is the dimensionality and Δ is tunneling energy between the localized states in the asymptonic T = 0 limit, in agreement with Imry's calculation. It is also found that calculated 1/τ_in deviates from T²(ln Δ/T)^d+1 as T increases, suggesting the importance of correction term at high temperature.     

Li mobility in Li0.5 − xNaxLa0.5TiO3 perovskites (0 ≤ x ≤ 0.5): Influence of structural and compositional parameters

The dependence of Li mobility on structure and composition of Li_0.5 − xNa_xLa_0.5TiO₃ perovskites (0 ≤ x ≤  0.5) has been investigated by means of neutron diffraction, nuclear magnetic resonance and impedance spectroscopy. At 300 K, all samples display a rhombohedral superstructure (R-3c S.G.), where octahedra are out of phase tilted along [111] direction of the ideal cubic cell. The elimination of the octahedral tilting is responsible for the rhombohedral–cubic transformation, detected near 1000 K. In these perovskites, La and Na cations are randomly distributed in A sites, but Li ions are fourfold coordinated at unit cell faces of the cubic perovskite. Lithium conductivity, σ_300 K, decreases with the sodium content, decreasing from values typical of fast ionic conductors, 10^− 3 S/cm, to those of good insulators, 10^− 10 S/cm, when the interconnectivity between vacant A sites is lost (x > 0.3). In samples with x < 0.3, dc conductivity displays a non-Arrhenius behaviour, decreasing activation energy from ~ 0.37 to 0.25 eV when the sample is heated between 77 and 500 K. The temperature dependence of B_Li factors shows the existence of two regimes for Li motion. Below 373 K, Li ions remain partially located near square oxygen windows that connect contiguous A sites, but above 400 K, extended Li motions become dominant. The additional decrease of activation energy from 0.25 to 0.16 eV (low-temperature ⁷Li NMR value), should require the full elimination of octahedral tilting which is only produced above 1000 °C.     

Densities, excess molar volumes, and viscosities of the binary and ternary mixtures of {diethylcarbonate (1) + p-chloroacetophenone (2) + 1-hexanol (3)} at 303.15 K for the liquid region and at ambient pressure

Densities ρ, dynamic viscosities η, of the ternary mixture (diethylcarbonate + p-chloroacetophenone + 1-hexanol) and the involved binary mixtures (diethylcarbonate + p-chloroacetophenone), (diethylcarbonate + 1-hexanol), and (p-chloroacetophenone + 1-hexanol) have been measured over the whole composition range at 303.15 K for the liquid region and at ambient pressure. The data obtained are used to calculate excess molar volumes V_m^E, excess partial molar volumes V¯_m,i^E, limiting excess partial molar volumes V¯_m,i^E,∞, and viscosity deviations Δη, of the binary and ternary mixtures. The data of excess molar volumes of the binary systems were fitted to the Redlich–Kister equation while for the ternary system the Cibulka equation was used. The McAllister's four body, and Kalidas and Laddha interaction models are used to correlate the kinematic viscosities of binary and ternary mixtures, respectively, to determine the fitting parameters and the standard deviations. The experimental data of the constitute binaries and ternary are analyzed to discuss the nature and strength of intermolecular interactions in these mixtures.     

Modified Kolmogorov wave turbulence in QCD matched onto “Bottom-up” thermalization

We investigate modification of Kolmogorov wave turbulence in QCD calculating gluon spectra as functions of time in the presence of a low energy source which feeds in energy density in the infrared region at a time-dependent rate. Then considering the picture of saturation constraints as has been constructed in the “bottom-up” thermalization approach we revisit that picture for RHIC center-mass energy, W=130 GeV, and also extend it to LHC center-mass energy, W=5500 GeV, thus for two cases having an opportunity to calculate the equilibration time, τ_eq|therm, of the gluon system produced in a central heavy ion collision at mid-rapidity region. Thereby, at RHIC and LHC energies we can match the equilibration time, obtained from the late stage gluon spectrum of the modified Kolmogorov wave turbulence, onto that of the “bottom-up” thermalization and other evolutional approaches as well. In addition, from the revised “bottom-up” approach we find the gluon liberation coefficient to be on the average, ε0.81–1.06 at RHIC and ε0.50–0.56 at LHC. We also present other phenomenological estimates of τ_therm which, at QCD realistic couplings, yield 0.45–0.65 fmτ_therm0.97–2.72 fm at RHIC and 0.31–0.40 fmτ_therm0.86–2.04 fm at LHC. We show that the second upper-bounds of τ_therm in both cases are due to the late stage gluon spectrum of the original Kolmogorov wave turbulence in QCD, previously deduced with a low energy source which feeds in energy density at a constant rate. On the other hand, the lower-bounds and first upper-bounds of τ_therm are due to the late stage gluon spectrum of the modified QCD wave turbulence, deduced here at the specific time-dependent rate. In the latter case, at certain conditions, taking also into account both very small and realistic couplings we give estimates: 0.65 fmτ_therm1.29 fm at RHIC and 0.52 fmτ_therm1.16 fm at LHC, as well as at realistic couplings we find 0.53<τ_therm<0.7 fm at RHIC and 0.41<τ_therm<0.65 fm at LHC.     

Lithium ion conductive glass–ceramics with Li3Fe2(PO4)3 and YAG laser-induced local crystallization in lithium iron phosphate glasses

The glasses with the composition of 37.5Li₂O–(25 − x)Fe₂O₃–xNb₂O₅–37.5P₂O₅ (mol%) (x = 5,10,15) are prepared, and it is found that the addition of Nb₂O₅ is effective for the glass formation in the lithium iron phosphate system. The glass–ceramics consisting of Nasicon-type Li₃Fe₂(PO₄)₃ crystals with an orthorhombic structure are developed through conventional crystallization in an electric furnace, showing electrical conductivities of 3 × 10^− 6 Scm^− 1 at room temperature and the activation energies of 0.48 eV (x = 5) and 0.51 eV (x = 10) for Li⁺ ion conduction in the temperature range of 30–200 °C. A continuous wave Nd:YAG laser (wavelength: 1064 nm) with powers of 0.14–0.30 W and a scanning speed of 10 μm/s is irradiated onto the surface of the glasses, and the formation of Li₃Fe₂(PO₄)₃ crystals is confirmed from XRD analyses and micro-Raman scattering spectra. The crystallization of the precursor glasses is considered as new route for the fabrication of Li₃Fe₂(PO₄)₃ crystals being candidates for use as electrolyte materials in lithium ion secondary batteries.     

Study of the process ee→ππγ in c.m. energy range 600–970 MeV at CMD-2

The cross section of the process e⁺e⁻→π⁰π⁰γ has been measured in the c.m. energy range 600–970 MeV with the CMD-2 detector. The following branching ratios have been determined:

Full-size image

and

Full-size image

. Evidence for the ρ⁰→f₀(600)γ decay has been obtained:

Full-size image

. From a search for the process e⁺e⁻→ηπ⁰γ the following upper limit has been obtained: at 90% CL.