Analisis of inelastic scattering of π-mesons from nuclei within the microscopic optical potential

Cross sections of inelastic scattering of π-mesons from Si, Ni, and Pb nuclei at energy T _lab = 291 MeV are calculated using the distorted wave approximation. The microscopic direct and transition optical potentials are determined by specifying the pion-nucleon scattering amplitude and the nuclear density distribution, where we use the in-medium πN amplitude parameters obtained earlier by analyzing the elastic scattering data for the same nuclei. The cross sections are calculated on the basis of the relativistic wave equation. The deformation parameters of the nuclei are obtained by comparing inelastic scattering cross sections with the appropriate experimental data.     

Interlayer-exciton mediated three-hole-Auger-decay in the π⁎-band of highly oriented pyrolytic graphite

Resonant photoemission spectroscopy (resPES) is used to probe the occupied π- and unoccupied π^⁎-bands of carbon thin films with particular focus on the Auger decay. Highly Oriented Pyrolytic Graphite (HOPG) is studied at the C1s edge. We find strong resonant features at 285.5 eV and 292 eV in the resPES diagram. The normal two-hole Auger decay proceeds under constant kinetic energy (45°) only in the σ^⁎-region. In the π^⁎-region, however, it proceeds under 67.5° in terms of a E_bind(ħω) diagram. We attribute this to a multiple Auger decay with a net three hole final state. For this novel decay process we propose a model. We discuss the long lifetime of the first resonant excitation and conclude that it arises from the strong excitonic character of the first resonant state. We use HOPG as a reference system and suggest that this novel process is a tool to identify interlayer–substrate interaction of the carbon layers involved.     

Elastic and inelastic scattering of π mesons on 7Li nuclei

Within the diffraction theory of multiple scattering, the differential cross sections for elastic and inelastic pion scattering on a ⁷Li nucleus are calculated for the case where the final nucleus is either in the ground or in the first excited state. The nuclear wave function is set to that in the αt cluster model. The sensitivity of the calculated observables to variations in the type of the wave functions for the alpha-particle and the triton cluster and for their relative motion is investigated. Various multiplicities of scattering and rescattering on the clusters constituting the ⁷Li nucleus are taken into account, and their contributions to the cross section are revealed. The results of the calculations are compared with experimental data at E _π=143, 164, and 194 MeV.     

Charge-symmetry-breaking effects from phase-shift analysis of elastic π± He scattering

A phase-shift analysis of elastic π^±4 He scattering at energies 20–160 MeV was performed to determine pure hadronic phase shifts. No statistically significant difference between the hadronic phase shifts deduced from π⁺⁴ He and π⁻⁴ He scattering was observed.     

π+ and π− elastic and inelastic scattering on 6Li at 100, 180 and 240 MeV

Angular distributions for scattering from ⁶Li with π⁺ and π⁻ beams were measured at 100, 180 and 240 MeV incident energy. Elastic (J^p = 1⁺, T = 0) and inelastic (J^p = 3⁺, T = 0, E_x = 2.19 MeV) data were obtained over large angular ranges. The elastic results are compared to calculations within the αnp cluster model.     

Determination of strange sea distributions from νN deep inelastic scattering

We present an analysis of the nucleon strange sea extracted from a global Parton Distribution Function fit including the neutrino and anti-neutrino dimuon data by the CCFR and NuTeV Collaborations, the inclusive charged lepton–nucleon Deep Inelastic Scattering and Drell–Yan data. The (anti-)neutrino induced dimuon analysis is constrained by the semileptonic charmed-hadron branching ratio Bμ=(8.8±0.5)%$B_{\mu }=(8.8\pm 0.5)\mathrm{\%}$, determined from the inclusive charmed hadron measurements performed by the FNAL-E531 and CHORUS neutrino emulsion experiments. Our analysis yields a strange sea suppression factor κ(20 GeV²)=0.62±0.04(exp.)±0.03(QCD)$\kappa (20{\text{GeV}}^2)=0.62\pm 0.04(\text{exp.})\pm 0.03(\text{QCD})$, the most precise value available, an x-distribution of total strange sea that is slightly softer than the non-strange sea, and an asymmetry between strange and anti-strange quark distributions consistent with zero (integrated over x   it is equal to S⁻(20 GeV²)=0.0013±0.0009(exp.)±0.0002(QCD)$S^{-}(20{\text{GeV}}^2)=0.0013\pm 0.0009(\text{exp.})\pm 0.0002(\text{QCD})$).     

Unraveling the nature of charge excitations in La₂CuO₄ with momentum-resolved Cu K-edge resonant inelastic x-ray scattering

The results of model calculations using exact diagonalization reveal the orbital character of states associated with different Raman loss peaks in Cu K-edge resonant inelastic x-ray scattering (RIXS) from La?CuO?. The model includes electronic orbitals necessary to highlight the nonlocal Zhang-Rice singlet, charge transfer, and d-d excitations, as well as states with apical oxygen 2p(z) character. The dispersion of these excitations is discussed with prospects for resonant final state wave-function mapping. A good agreement with experiments emphasizes the substantial multiorbital character of RIXS profiles in the energy transfer range 1-6 eV.     

Formation of ground and excited hydrogen atoms in proton–potassium inelastic scattering

The inelastic scattering of proton with a potassium atom is treated for the first time as a three-channel problem within the framework of the improved coupled static approximation by assuming that the ground (1s state) and the excited (2s state) hydrogen formation channels are open for seven values of total angular momentum, ? (0≤?≤6) at energies between 50 and 500 keV. The Lipmann–Swinger equation and the Green’s function iterative numerical method are used to calculate iterative partial and total cross-sections. This can be done by calculating the reactance matrix at different values of the considered incident energies to obtain the transition matrix that gives partial and total cross-sections. Present results are in reasonable agreement with previous results.     

A three channel model of ππ scattering and the elastic and inelastic electromagnetic vertex functions

A three channelN/D model of π π scattering, the pion form factor, ande ⁺ e ^?→4π cross sections is investigated. The dispersion relation subtraction constants and other parameters are chosen to optimize resonances are generated, the ρ(770) and ρ(1600), and that there is no ρ(1250) resonant state.     

Photoproduction of K 0 and Λ at HERA and a comparison with deep inelastic scattering

Inclusive K ⁰ and Λ photoproduction has been investigated at HERA with the H1 detector at an average photon-proton center of mass energy of 200 GeV in the transverse momentum range 0.5 < p _t < 5 GeV. The production rates as a function of p _t and center of mass rapidity are compared to those obtained in deep inelastic scattering at 〈Q ²〉 = 23 GeV². A similar comparison is made of the rapidity spectra of charged particles. The rate of strangeness photoproduction is compared with $p\bar p$ measurements. The observations are also compared with next-to-leading order QCD calculations and the predictions of a Monte Carlo model.     

Determination of the pattern of nuclear binding from the data on lepton–nucleus deep inelastic scattering

Nucleon structure function ratios measured in the range of atomic masses are analyzed with the aim of determining the pattern of the x and A dependence of modifications caused by the nuclear environment. It is found that the x and A dependence of the deviations of the from unity can be factorized in the entire range of x. The characteristic feature of the factorization is represented with the three cross-over points , i = 1–3 in which independently of A. In the range the pattern of is fixed with . The pattern of the x dependence is compared with theoretical calculations of Burov, Molochkov and Smirnov to demonstrate that the evolution of the nucleon structure as a function of A occurs in two stages: first for and second for . The long-standing problem of the origin of the EMC effect is understood as a modification of the nucleon structure in the field responsible for the binding forces in a three-nucleon system. Received: 28 January 1999 / Revised version: 1 April 1999 / Published online: 3 August 1999     

Nuclear fusion and sticking from resonant states of dtμ

Fusion rates and sticking fractions for s-symmetry resonant states that cluster below the (t)_2s + d threshold in the molecular continuum of dt are analyzed. The fusion rates for some of these states are found to be comparable to their particle decay rates. The associated sticking probabilities appear to be approximately one order of magnitude lower than that of the ground state. This feature is interpreted as a result of quantum interference effects arising from the nonadiabatic character of the metastable states and indicates that the muon catalyzed fusion might proceed more efficiently if it were to occur from molecular resonant states.     

Ordering and growth of Langmuir–Blodgett films: X-ray scattering studies

The interplay of ordering, confinement and growth in ultrathin films gives rise to various interesting phenomena not observed in bulk materials. The nature of ordering and interfacial morphology present in these films, in turn, depends on their growth mechanism. Well-ordered metal–organic films, deposited using an enigmatic Langmuir–Blodgett (LB) technique, are not only ideal systems for understanding the interplay between growth and structure of ultrathin films but also for studying chemical reactions and phase transitions in confined geometries. Studies on these LB films also enhance our understanding of the fundamental interactions of amphiphilic molecules important for biological systems. Advent of grazing incidence X-ray scattering techniques has enabled us to probe the interfacial structure of these multilayer films at very high resolution and as a result has improved our knowledge about the mechanism of growth processes and about physical/chemical properties of ultrathin films. In this review we will focus our attention on recent results obtained using these X-ray scattering techniques to understand the mechanism of growth leading to formation of remarkably well-ordered LB films after giving a brief outline of these scattering techniques. In addition, we also review recent results on growth and structure of nanoparticles formed by suitable chemical processes within the ordered matrix of LB films. Finally, we will discuss the work done on melting of LB films and its implications in our understanding of melting process in lower dimensions. In all these studies, especially those on as-deposited LB films results of atomic force microscopy measurements have provided important complementary morphological information.     

Breakup effects of 6,7li on elastic and inelastic scattering from 12C at 18–28 MeV/nucleon

The differential cross sections for elastic scattering of ^6,7Li from ¹²C and inelastic one from the lowest three excited states of ¹²C have been measured at bombarding energies of 18–28 MeV/nucleon. Theoretical analyses of the data have been performed in which consistent treatments of density distributions for the ground and excited states of both projectile and target nuclei are made in the framework of microscopic cluster models for ^6,7Li and ¹²C and projectile-target interactions are generated by the double folding of the M3Y effective nucleon-nucleon interaction. About 25% reduction of the real part of folded potentials is required both in the analyses of elastic scattering with the single-channel calculation and in those of inelastic scattering with the coupled-channel calculation including the excited states of ¹²C. This reduction can be explained as a projectile breakup effect on elastic and inelastic scattering in comparison with a coupled-discretized-continuum-channels (CDCC) calculation and an extended CDCC one which allows mutual excitations of both projectile and target nuclei for ⁶Li case, respectively. It is also seen that an effect due to the target excitation on elastic scattering is of less importance than that of the ^6,7Li projectile breakup processes even fora deformed nucleus like ¹²C. Discrepancy between the extended CDCC calculation and inelastic data for the 0⁺₂ state of ¹²C suggests a strong influence from the ¹²C → 3α breakup channels in the ⁶Li case.     

Studies of high-temperature electron–phonon interactions with inelastic neutron scattering and first-principles computations

Several recent studies of phonons combining inelastic neutron scattering and first-principles calculations are summarized. Inelastic neutron scattering was used to measure the phonon densities of states of the A15 compounds V₃Si, V₃Ge, and V₃Co at temperatures from 10 K to 1273 K. It was found that phonons in V₃Si and V₃Ge, which are superconducting at low temperatures, exhibit an anomalous stiffening with increasing temperature, whereas phonons in V₃Co have a normal softening behavior. Additional measurements of the phonon DOS of BCC V alloys were performed, and it was found that a stiffening anomaly present in pure V is suppressed upon introduction of extra d-electrons by alloying. First-principles calculations of the electronic and phonon densities of states show that in both these systems, the anomalous phonon stiffening originates with an adiabatic electron–phonon coupling mechanism. The anomaly is caused by the thermally-induced broadening of sharp peaks in the electronic density of states, which tends to decrease the electronic density at the Fermi level. These results illustrate how the combined use of first-principles calculations and inelastic neutron scattering provides powerful insights into couplings of excitations in condensed-matter.     

Asymmetry measurement of the polarized Σ+p elastic scattering and the hyperon-nucleon spin-orbit interaction

In order to study the hyperon-nucleon spin-orbit interaction, asymmetries of the polarized Σ⁺ elastic scattering on protons have been measured. The polarized hyperons were produced through the p(π⁺, K⁺) Σ⁺ reaction in a liquid-scintillator active target, and tracks of Σ⁺p scattering events were recorded with a newly developed track detector named SCITIC (scintillating track image camera). Although analyses of 10 times more data with more sophisticated data-taking systems and more elaborated analyzing tools are under way, data from an early stage of this experiment indicate a large Σ⁺p spin-orbit interaction in contrast to the case of the small ΛN spin-orbit interaction. Received: 27 May 2002 / Accepted: 23 July 2002 / Published online: 19 November 2002 RID="a" ID="a"e-mail: nakai@post.kek.jp Communicated by Th. Walcher     

Sign of nuclear electric quadrupole coupling constants in solids fromγ-ray anisotropy measurements after capture of polarized neutrons

An experimental method is presented which allows the determination of the sign of nuclear electric quadrupole interactions in solids. Activated target nuclei with a purely dipolar spin polarization are produced by capture of polarized thermal neutrons. The quadrupole coupling of the nuclei to the electric field gradient tensor in the target crystal converts this (dipolar) polarization partly into a (quadrupolar) alignment, which can be measured by the anisotropy of the-ray emission in a succeeding nuclear transition. The sign of the alignment created in this reorientation process depends on the sign of the electric quadrupole interaction. The reorientation effect can be enhanced by selective induction of nuclear magnetic resonance transitions. The method has been applied to measure the sign of the crystal electric field gradient (efg) in tetragonal MgF₂. Further, the sign of an efg in cubic CaF₂ originating from a¹⁹F interstitial adjacent to the activated²⁰F probe nucleus has been determined. The method is in principle applicable to a considerable number of nuclides.