Nuclear transparency in the (e,${\mathit{e}}^{\prime }$p) reaction for 135≤${\mathit{T}}_{\mathit{p}}$≤800 MeV is investigated using the distorted-wave approximation. Calculations using density-dependent effective interactions, both empirical and theoretical, are compared with phenomenological optical potentials. We find that nuclear transparency is well correlated with proton absorption and neutron total cross sections and that calculations using density-dependent effective interactions provide the best agreement with data. Nuclear transparency calculations are compared with recent electron scattering data for ${\mathit{Q}}^2$<2 (GeV/c${)}^2$. For ${\mathit{T}}_{\mathit{p}}$≲200 MeV we find that there is considerable sensitivity to the choice of optical model and that the empirical effective interaction provides the best agreement with the data, but remains 5–10 % low. For ${\mathit{T}}_{\mathit{p}}$≳300 MeV we find that there is much less difference between these models, but that the calculations significantly underpredict transparency data and that the discrepancy increases with A. The differences between Glauber and optical model calculations are related to their respective definitions of the semi-inclusive cross section. By using a more inclusive summation over final states the Glauber model emphasizes nucleon-nucleon inelasticity, whereas with a more restrictive summation the optical model emphasizes nucleon-nucleus inelasticity; experimental definitions of the semi-inclusive cross section lie between these extremes. © 1996 The American Physical Society.

In order to prepare the analysis of planned elastic-scattering experiments with a low-energy radioactive ${}_{}{}^6{}_{}{}^{}\mathrm{He}$ beam on an α target, we determine a theoretical interaction between these nuclei. A double-folding potential is obtained from a realistic ${}_{}{}^6{}_{}{}^{}\mathrm{He}$ density derived from a microscopic three-cluster model. Special attention is paid to the ${}_{}{}^6{}_{}{}^{}\mathrm{halo}$ description. The resulting potential displays an unusual long tail which might have observable effects on the elastic cross sections. The parity dependence of the optical potential related to the elastic transfer of the halo neutrons is discussed qualitatively. © 1996 The American Physical Society.

The sensitivity of nucleon-nucleus elastic scattering to the off-shell behavior of realistic nucleon-nucleon interactions is investigated when on-shell equivalent nucleon-nucleon potentials are used. The study is based on applications of the full-folding optical model potential for an explicit treatment of the off-shell behavior of the nucleon-nucleon effective interaction. Applications were made at beam energies between 40 and 500 MeV for proton scattering from ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ and ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$. We use the momentum-dependent Paris potential and its local on-shell equivalent as obtained with the Gelfand-Levitan and Marchenko inversion formalism for the two nucleon Schrödinger equation. Full-folding calculations for nucleon-nucleus scattering show moderate fluctuations in the corresponding observables. This sets narrow margins within which off-shell features of the nucleon-nucleon interaction can be resolved. Based on these results, inversion potentials were also constructed directly from phenomenological phase shifts (SM94). Their use in nucleon-nucleus scattering at intermediate energies provides an improved description of the data relative to those obtained from current realistic potential models. © 1996 The American Physical Society.

An algorithm is presented to adjust the uncorrelated momentum vectors of identical bosons produced by models of relativistic heavy-ion collisions to reproduce two-body and three-body Bose-Einstein correlation functions. The method is used to study the quality of the three-body correlations predicted by calculations in which prescribed two-body correlation functions are fit and to study the effects on the two-body distributions when the three-body correlations help constrain the momentum vector adjustment procedure. © 1996 The American Physical Society.

We investigate the thermalization and the chemical equilibration of a parton plasma created from Au+Au collision at LHC and RHIC energies starting from the early moment when the particle momentum distributions in the central region become for the first time isotropic due to longitudinal cooling. Using the relaxation time approximation for the collision terms in the Boltzmann equations for gluons and for quarks and the real collision terms constructed from the simplest QCD interactions, we show that the collision times have the right behavior for equilibration. The magnitude of the quark (antiquark) collision time remains bigger than the gluon collision time throughout the lifetime of the plasma so that gluons are equilibrating faster than quarks both chemically and kinetically. That is we have a two-stage equilibration scenario as has been pointed out already by Shuryak sometimes ago. Full kinetic equilibration is however slow and chemical equilibration cannot be completed before the onset of the deconfinement phase transition assumed to be at ${\mathit{T}}_{\mathit{c}}$=200 MeV. By comparing the collision entropy density rates of the different processes, we show explicitly that inelastic processes, and not elastic processes as is commonly assumed, are dominant in the equilibration of the plasma and that gluon branching leads the other processes in entropy generation. We also show that, within perturbative QCD, processes with higher power in ${\mathrm{\alpha }}_{\mathit{s}}$ need not be less important for the purpose of equilibration than those with lower power. The state of equilibration of the system has also a role to play. We compare our results with those of the parton cascade model. © 1996 The American Physical Society.

The effect of surface fluctuations on the observables of a quark-hadron phase transition is studied. The Ginzburg-Landau formalism is extended by the inclusion of an extra term in the free energy that depends on the vertical displacements from a flat surface. The probability that a bin has a particular net displacement is determined by lattice simulation, where the physics input is color confinement. The surface fluctuations from bin to bin are related to multiplicity fluctuations, which in turn are measured by the factorial moments. It is found that both the F-scaling behavior and the scaling exponent are essentially unaffected by the inclusion of surface fluctuations. © 1996 The American Physical Society.

Measurements of dilepton production from charm decay and Drell-Yan processes, respectively, probe the gluon and sea quark distributions in hadronic collisions. In nucleus-nucleus collisions, these hard scattering processes constitute a ‘‘background’’ to thermal contributions from the hot matter produced by the collision. To determine the magnitude and behavior of this background, we calculate the hard scattering contribution to dilepton production in nuclear collisions at RHIC and LHC at next to leading order in perturbative QCD. Invariant mass, rapidity, and transverse momentum distributions are presented. We compare these results to optimistic hydrodynamic estimates of the thermal dilepton production. We find that charm production from hard scattering is by far the dominant contribution. Experiments therefore can measure the gluon distribution in the nuclear target and projectile and, consequently, can provide new information on gluon shadowing. We then illustrate how experimental cuts on the rapidity gap between the leptons can aid in reducing the charm background, thereby enhancing thermal information. © 1996 The American Physical Society.

Coherent effects are considered in the model of bremsstrahlung of scalar pions in high-energy nucleus-nucleus collisions. As a result of the quantum mechanical Monte Carlo calculation it is shown that this mechanism yields pions in central collisions at large rapidities with a strong coherence. The coherent enhancement of the cross section has a threshold character of a function of the number of interacting nucleon pairs. The coherence narrows regions of pion transverse momenta towards zero and longitudinal momenta around some characteristic value. The pion pseudorapidities are moved to large values of about one-half of a unit. © 1996 The American Physical Society.

Self-consistent solitonic solutions with baryon number one are obtained in the chiral quark sigma model. The translational invariant vacuum is stabilized by a Landau ghost subtraction procedure based on the requirement of the Källén-Lehmann (KL) representation for the meson propagators. The connection of this ghost free model (KL model) to the more popular Nambu-Jona-Lasinio (NJL) model is discussed in detail. © 1996 The American Physical Society.

The numerical solution of the relativistic quasipotential equation is presented. A new approach is introduced to express the Blankenbecler-Sugar-Logunov-Tavkhlidze equation and the equal-time equation which is equivalent to the full Salpeter equation, improved by adding the crossed box diagram as energy eigenstates. A set of coupled positive and negative energy eigenstates is obtained. A systematic method to solve the nonlinear eigenvalue problem of the bound state equation is given and the results are compared with the approximate versions of the standard eigenvalue of the bound state. These equations are used in the investigation of heavy and light mesons with vector Coulomb and scalar linear confining potentials. © 1996 The American Physical Society.

An effective Hamiltonian consisting of bare Δ⇆πN, γN vertex interactions and energy-independent meson-exchange πN⇆πN,γN transition operators is derived by applying a unitary transformation to a model Lagrangian with N,Δ,π, ρ, ω, and γ fields. With appropriate phenomenological form factors and coupling constants for ρ and Δ, the model can give a good description of πN scattering phase shifts up to the Δ excitation energy region. It is shown that the best reproduction of the recent LEGS data of the photon-asymmetry ratios in γp→${\mathrm{\pi }}^0$p reactions provides rather restricted constraints on the coupling strengths ${\mathit{G}}_{\mathit{E}}$ of the electric E2 and ${\mathit{G}}_{\mathit{M}}$ of the magnetic M1 transitions of the bare Δ⇆γN vertex and the less well-determined coupling constant ${\mathit{g}}_{\mathrm{\omega }\mathit{NN}}$ of ω meson. Within the ranges that ${\mathit{G}}_{\mathit{M}}$=1.9±0.05, ${\mathit{G}}_{\mathit{E}}$=0.0±0.025, and 7≤${\mathit{g}}_{\mathrm{\omega }\mathit{NN}}$≤10.5, the predicted differential cross sections and photon-asymmetry ratios are in an overall good agreement with the data of γp→${\mathrm{\pi }}^0$p, γp→${\mathrm{\pi }}^{+}$n, and γn→${\mathrm{\pi }}^{\mathrm{-}}$p reactions from 180 MeV to the Δ excitation region. The predicted ${\mathit{M}}_{1^{+}}$ and ${\mathit{E}}_{1^{+}}$ multipole amplitudes are also in good agreement with the empirical values determined by the amplitude analyses. The constructed effective Hamiltonian is free of the nucleon renormalization problem and hence is suitable for nuclear many-body calculations. We have also shown that the assumptions made in the K-matrix method, commonly used in extracting empirically the γN→Δ transition amplitudes from the data, are consistent with our meson-exchange dynamical model. It is found that the helicity amplitudes calculated from our bare γN→Δ vertex are in good agreement with the predictions of the constituent quark model. The differences between these bare amplitudes and the dressed amplitudes, which are closer to the empirical values listed by the Particle Data Group, are shown to be due to the nonresonant meson exchange mechanisms. Within the range 7≤${\mathit{g}}_{\mathrm{\omega }\mathit{NN}}$≤10.5 of the ω meson coupling favored by the data of the photon-asymmetry ratios in γp→${\mathrm{\pi }}^0$p reactions, our values of the E2/M1 ratio for the γN→Δ transition are (0.0±1.3)% for the bare vertex and (-1.8±0.9)% for the dressed vertex. © 1996 The American Physical Society.

A search for ν${\mathrm{¯}}_{\mathrm{\mu }}$→ν${\mathrm{¯}}_{\mathit{e}}$ oscillations has been conducted at the Los Alamos Meson Physics Facility using ν${\mathrm{¯}}_{\mathrm{\mu }}$ from ${\mathrm{\mu }}^{+}$ decay at rest. The ν${\mathrm{¯}}_{\mathit{e}}$ are detected via the reaction ν${\mathrm{¯}}_{\mathit{ep}}$→${\mathit{e}}^{+}$n, correlated with the 2.2 MeV γ from np→dγ. The use of tight cuts to identify ${\mathit{e}}^{+}$ events with correlated γ rays yields 22 events with ${\mathit{e}}^{+}$ energy between 36 and 60 MeV and only 4.6±0.6 background events. The probability that this excess is due entirely to a statistical fluctuation is 4.1×${10}^{\mathrm{-}8}$. A ${\mathrm{\chi }}^2$ fit to the entire ${\mathit{e}}^{+}$ sample results in a total excess of 51.$0_{\mathrm{-}19.5}^{+20.2\mathrm{}}$±8.0 events with ${\mathit{e}}^{+}$ energy between 20 and 60 MeV. If attributed to ν${\mathrm{¯}}_{\mathrm{\mu }}$→ν${\mathrm{¯}}_{\mathit{e}}$ oscillations, this corresponds to an oscillation probability (averaged over the experimental energy and spatial acceptance) of (0.31±0.12±0.05)%. © 1996 The American Physical Society.

The internal bremsstrahlung spectrum which accompanies the electron capture decay of ${}_{}{}^{139}{}_{}{}^{}\mathrm{Ce}$ to the first excited state of ${}_{}{}^{139}{}_{}{}^{}\mathrm{La}$ has been measured in coincidence with the nuclear gamma ray which deexcites that state. The measured intensity above 42 keV is found to be (1.070±0.024) times that predicted by the recent calculations of Surić et al. The ${\mathit{Q}}_{\mathrm{EC}}$ value is found to be 264.6±2.0 keV. © 1996 The American Physical Society.

We report measurements of capture rates and hyperfine dependences in muon capture on ${}_{}{}^{23}{}_{}{}^{}\mathrm{Na}$ to various states in Ne and F isotopes. We also report comparisons of the capture rates and hyperfine dependences for six ${}_{}{}^{23}{}_{}{}^{}\mathrm{Na}$ → ${}_{}{}^{23}{}_{}{}^{}\mathrm{Ne}$ transitions with the 1s-0d shell model with the empirical effective interaction of Brown and Wildenthal and the realistic effective interaction of Kuo and Brown. Fits to the data with the Brown and Wildenthal interaction yield an effective coupling ${\mathit{g}\mathit{̃}}_{\mathit{a}}$ = -1.01 ± 0.07 and an effective coupling ratio ${\mathit{g}\mathit{̃}}_{\mathit{p}}$/${\mathit{g}\mathit{̃}}_{\mathit{a}}$ = 6.5 ± 2.4. The value of ${\mathit{g}\mathit{̃}}_{\mathit{a}}$ is consistent with values of ${\mathit{g}\mathit{̃}}_{\mathit{a}}$ extracted from ${\mathrm{\beta }}^{+}$/${\mathrm{\beta }}^{\mathrm{-}}$ decay and (p,n)/(n,p) charge exchange data, and the value of ${\mathit{g}\mathit{̃}}_{\mathit{p}}$/${\mathit{g}\mathit{̃}}_{\mathit{a}}$ is consistent with the predictions of PCAC and pion-pole dominance. We evaluate the nuclear model dependence of these values of ${\mathit{g}\mathit{̃}}_{\mathit{a}}$ and ${\mathit{g}\mathit{̃}}_{\mathit{p}}$/${\mathit{g}\mathit{̃}}_{\mathit{a}}$ and examine the role of the Gamow-Teller and other matrix elements in the ${}_{}{}^{23}{}_{}{}^{}\mathrm{Na}$ → ${}_{}{}^{23}{}_{}{}^{}\mathrm{Ne}$ transitions. © 1996 The American Physical Society.

The neutron capture cross sections of ${}_{}{}^{116}{}_{}{}^{}\mathrm{Sn}$, ${}_{}{}^{118}{}_{}{}^{}\mathrm{Sn}$, and ${}_{}{}^{120}{}_{}{}^{}\mathrm{Sn}$, which were determined recently with the Karlsruhe 4π ${\mathrm{BaF}}_2$ detector, have been reanalyzed at low energies. Resonance parameters were extracted by means of a shape analysis program, thus allowing a more reliable determination of the averaged cross sections below 20 keV. This study confirms the previously reported stellar cross sections. Accordingly, the results of the s-process studies based on these data remain unchanged. © 1996 The American Physical Society.

Neutrino induced reactions on ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, an ingredient of liquid scintillators, have been studied in several experiments. We show that for currently available neutrino energies, ${\mathit{E}}_{\nu }$≤ 300 MeV, calculated exclusive cross sections ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}_{\mathrm{g}.\mathrm{s}.\mathrm{}}^{}{}_{}{}^{}$(ν,l${)}^{12}$${\mathrm{N}}_{\mathrm{g}.\mathrm{s}.\mathrm{}}$ for both muon and electron neutrinos are essentially model independent, provided the calculations simultaneously describe the rates of several other reactions involving the same states or their isobar analogs. The calculations agree well with the measured cross sections, which can be therefore used to check the normalization of the incident neutrino spectrum and the efficiency of the detector. © 1996 The American Physical Society.

The superfluid densities in a mixture of neutron and proton superfluids are discussed within Fermi-liquid theory. There are the usual diagonal densities ${\mathrm{\rho }}_{\mathit{nn}}$ and ${\mathrm{\rho }}_{\mathit{pp}}$ but also off-diagonal densities ${\mathrm{\rho }}_{\mathit{np}}$ and ${\mathrm{\rho }}_{\mathit{pn}}$ which represent coupling between the two species. We express these quantities solely in terms of the Fermi momenta and the Landau parameter ${\mathit{f}}_1^{\mathit{pn}}$ in a way that explicitly satisfies the Galilean invariance constraints ${\mathrm{\rho }}_{\mathit{pp}}$+${\mathrm{\rho }}_{\mathit{pn}}$=${\mathit{m}}_{\mathit{pn}\mathit{p}}$ and ${\mathrm{\rho }}_{\mathit{nn}}$+${\mathrm{\rho }}_{\mathit{pn}}$=${\mathit{m}}_{\mathit{nn}\mathit{n}}$. The results are of astrophysical interest, e.g., in a discussion of the damping of gravitational instability in rapidly rotating neutron stars or of post-glitch relaxation of pulsars. © 1996 The American Physical Society.

We calculate the reaction cross sections for the fusion of hydrogen and deuterium in strong magnetic fields as are believed to exist in the atmospheres of neutron stars. We find that in the presence of a strong magnetic field (B≳${10}^{12}$ G), the reaction rates are many orders of magnitude higher than in the unmagnetized case. The fusion of both protons and deuterons is important over a neutron star’s lifetime for ultrastrong magnetic fields (B∼${10}^{16}$ G). The enhancement may have dramatic effects on thermonuclear runaways and bursts on the surfaces of neutron stars. © 1996 The American Physical Society.

The β-delayed γ decay of ${}_{}{}^{108}{}_{}{}^{}\mathrm{Nb}$ has been studied using the on-line mass-separator technique. The measured β-decay half-life 0.20±0.03 s agrees with the previous measurement based on β-delayed neutron detection. The lifetime of the first $2^{+}$ state in ${}_{}{}^{108}{}_{}{}^{}\mathrm{Mo}$ was measured to be 0.5±0.3 ns, which is consistent with a deformation β≊0.4. Spin and parity of $2^{+}$ are suggested for the ground state of ${}_{}{}^{108}{}_{}{}^{}\mathrm{Nb}$. © 1996 The American Physical Society.

A superdeformed band has been observed in the ${}_{}{}^{147}{}_{}{}^{}\mathrm{Tb}$ nucleus which was produced with the reaction ${}_{}{}^{100}{}_{}{}^{}\mathrm{Mo}$${(}^{51}$V,4n${)}^{147}$Tb at a bombarding energy of 230 MeV. The band configuration is assigned as π$6^3$ν$7^1$ with a total parity and signature of (π,α)=(-,+1/2). © 1996 The American Physical Society.