Resonances in electron scattering and photon absorption

A short survey is given of the development of ideas about resonances in atomic scattering processes and their connection with the theory of resonant states in nuclei, impurity resonances in solids, ion-atom scattering and recombination in plasmas. A detailed discussion of the experimental situation for atomic resonances is then given, followed by a review of the theory of resonance reactions as applied to them. Special attention is given to effective range and quantum defect methods, and to Fano's configuration interaction theory. Theoretical results for line positions, shapes and widths are compared with experimental data and the need for more angular distribution data is emphasized.     

Properties of baryon resonances from a multichannel partial wave analysis

Properties of nucleon and Δ resonances are derived from a multichannel partial wave analysis of pion and photo-induced reactions off protons. This paper summarizes the latest results on masses, widths, and decay properties of nucleon and Δ resonances.     

Barrier-top resonances and heavy ion reactions

In reactions involving strong absorption, we show that the narrowest potential (two body) resonances may be of a novel type, barrier-top (or “orbiting”) resonances whose ReE are at the centrifugal-Coulomb barrier top and whose wave functions are localized at the barrier radius. These resonances provide the link between semiclassical orbiting and quantal Regge poles and establish the close relationship between these concepts. We exploit the dominance and simplicity of barrier-top scattering in a model in which direct reaction amplitudes for heavy ion particle transfers can be calculated analytically. The model assumes complete absorption at small r of inward propagating waves, and a parabolic barrier potential which approximates the optical potential in the barrier region; the wave functions of the model (Weber functions) correspondingly approximate the optical potential wave functions (distoreed waves) in the barrier region. The results of this model reproduce many of the features present in more detailed DWBA computations, and provide simple physical explanations for these features.     

Microscopic form factors for inelastic excitation of isovector modes in heavy-ion reactions

Microscopic form factors are calculated for the excitation of isovector modes in heavy-ion reactions. They are constructed from RPA model wave functions. For the case of giant dipole resonances, the results are compared with the Goldhaber-Teller and Jensen-Steinwedel macroscopic expressions.     

Study of nucleon resonances in a chiral quark model via η productions

In this report we investigate η-meson productions on the proton via electromagnetic and hadron probes in a chiral quark model approach. The observables, such as, differential cross section and beam asym-metry for the two productions are calculated and compared with the experiment. The five known resonances S_(11)(1535), S_(11)(1650), P_(13)(1720), D_(13)(1520), and F_(15)(1680) are found to be dominant in the reaction mech-anisms in both channels. Significant contribution from a new S_(11) resonances are deduced. For the so-called "missing resonances", no evidence is found within the investigated reactions. The partial wave amplitudes for π~-p→ηn are also presented.     

Few-body Decay and Recombination in Nuclear Astrophysics

Three-body continuum problems are investigated for light nuclei of astrophysical relevance. We focus on three-body decays of resonances or recombination via resonances or the continuum background. The concepts of widths, decay mechanisms and dynamic evolution are discussed. We also discuss results for the triple ?? decay in connection with 2⁺ resonances and density and temperature dependence rates of recombination into light nuclei from ??-particles and neutrons.     

QED effects in Cu-like Pb recombination resonances near threshold

In an electron-ion recombination study with Pb53+ dielectronic recombination resonances are found for as low as approximately 10(-3)-10(-4) eV relative energy. The resonances have been calculated by relativistic many-body perturbation theory and through comparison with experiment the Pb53+(4p(1/2)-4s(1/2)) energy splitting of approximately 118 eV is determined with an accuracy comparable to the position of the first few resonances, i.e., approximately 10(-3) eV. Such a precision provides a test of QED in a many-body environment at a level which can still not be reached in calculations.     

A theory of intermediate structure,overlapping resonances and photonuclear reactions in light nuclei

Starting from a many body Hamiltonian a general theory involving intermediate structures and overlapping resonances in nuclear reaction has been worked out. This treatment, based on Trefftz's work on dielectronic recombination in atomic physics, avoids explicit use of projection operators and all relevant quantities like decay widths and energy shifts are explicitly expressed in terms of two body matrix elements. In particular, attention has been focused on the interaction of bound states among themselves and then on the coupling of the continuum with these interacting bound states. For the case of overlapping resonances, it is shown that in general one cannot take a simple energy average of the resonant amplitudes, and explicit equations for this case have been obtained. This microscopic theory also provides a justification of the model of Duke, Malik, and Firk in explaining the intermediate structure in giant dipole resonance region of ¹⁶O and ²⁸Si. However, the formalism is a general one and is suitable for the study of intermediate structure involving isolated and overlapping resonances for many types of reactions.     

Spontaneous emission in the near-resonant kapitza-dirac effect

We study the influence of spontaneous emission on atom diffraction by a standing wave laser field. We characterize, analytically, the major regimes of the near-resonant Kapitza-Dirac effect and study, numerically, the influence of spontaneous emission. In particular, we discuss in some detail two important classes of two-beam resonances which are major candidates to develop effective atom beam splitters, the so-called Bragg and Doppleron resonances.     

Photoproduction of multi-meson final states-recent results from the Crystal-Barrel/TAPS experiment at ELSA-

Multi-meson final states such as γp→pπ~0π~0 and γp → pπ~0η have been investigated with the Crystal-Barrel/TAPS experiment at ELSA. Baryon cascades via △π and △η and also via higher mass baryon resonances are clearly observed. Based on this data and on data from other reactions a partial wave analysis has been performed from which partial decay widths of various N~* and △~* states into the different pπ~0π~0 and pπ~0η decay channels have been determined, leading partly to unexpected results. In addition, polarisation observables have been investigated. The beam asymmetry Σ has been determined for both reactions and double polarisation data using a longitudinally polarised target and a circularly or linearly polarised photon beam has been taken. Given the angular coverage of the Crystal-Barrel/TAPS experiment this data covers almost the full angular range and phase space. This data will provide new and important information for the partial wave analyses and bring us one step closer towards a complete experiment.     

Three-boson problem near a narrow Feshbach resonance

We consider a three-boson system with resonant binary interactions and show that for sufficiently narrow resonances three-body observables depend only on the resonance width and the scattering length. The effect of narrow resonances is qualitatively different from that of wide resonances revealing novel physics of three-body collisions. We calculate the rate of three-body recombination to a weakly bound level and the atom-dimer scattering length and discuss implications for experiments on Bose-Einstein condensates and atom-molecule mixtures near Feshbach resonances.     

Time delay in nuclear reactions

The time delays involved under different circumstances in nuclear reactions, e.g., isolated or overlapping resonances, are analysed from the unified point of view of unitarity and of the statistical and analytical properties of theS-matrix. A general theorem is proved which says that the average over then open channels of the time delay of a wave packet covering many resonances (whose average separation isD) is given by?/(nD). The case of an incoherent superposition of monochromatic beams is also studied and the corresponding time delay is evaluated in the statistical model of Ericson.     

Fano resonances in prism-coupled multimode square micropillar resonators

We report Fano resonances in a multimode square glass micropillar resonator; the resonances were obtained by using angle-resolved prism coupling. Our experiments reveal characteristically asymmetric line shapes of high-Q resonances and of detuned low-Q resonances in multimode reflection spectra. The asymmetric resonance line shapes evolve for an approximately pi phase within a 0.5 degree range of reflection angles. We model our observed asymmetric multimode resonances by the far-field interference between a light wave that is evanescently coupled with a high-Q mode orbit and a coherent light wave that is refractively coupled with a detuned low-Q mode orbit.     

Possibility of new resonances in transient nonlinear spectroscopy

We predict the existence of new types of extra resonances in transient four wave mixing from a system with negligible collisions. These new resonances arise from the coherent pumping and disappear in the long time limit. We give explicit results for extra resonances in four wave mixing from several conventonally used systems.     

Resonant light pressure forces in a strong standing laser wave

The light pressure forces acting on a two-level atom in a strong standing laser wave are calculated. It is shown that at strong saturation of a resonant atomic transition the velocity dependence of these forces include sharp variations due to multiphoton resonances. At small atomic velocities these multiphoton resonances may even change the sign of the forces. The results obtained are important for many applications of resonant light pressure, e.g. in cooling and trapping of atoms in standing laser waves.     

Electronic energy exchange in high-temperature air

Kinetic processes with the participation of electronic states of atoms and molecules in air behind the shock wave front were analyzed. All metastable levels of molecular and atomic oxygen and nitrogen and nitrogen oxide molecules situated below the dissociation energy were analyzed. In high-temperature air, atom and molecule electronic states are formed in dissociation and recombination, electronic energy exchange in collisions of particles, and chemical exchange reactions. The formation of excited electronic states in the recombination of atoms and isoenergy vibrational energy transfer from highly excited vibrational levels into electronic energy is the fastest process. The quenching of metastable particles occurs in collisions between particles, dissociation and recombination, and chemical exchange reactions. A database on electronic energy exchange rate constants in high-temperature air is presented.     

离子和冷却电子重组的高分辨谱研究(英文)

给出了在CRYRING重离子储存环上测量到的在很低能量下电子与离子重组的最新实验结果和有关速率系数增强的新的数据 .主要讨论类锂、类钠和类铜离子的共振双电子重组的新近测量结果 ,以及从这些共振谱中所导出的非常精确的离子能级劈裂值 ,从而将严格检验相对论效应、电子关联效应和量子电动力学效应 .其中 ,对类锂Kr3 3 + 离子 2s1/2 能级Lamb移位的确定精度达到了0 .1%. We present our latest results on recombination of electrons with ions at very low energies obtained at the CRYRING heavy-ion storage ring. New data on the enhanced rate coefficient are shown. Then we concentrate on recent measurements of dielectronic recombination resonances with Li-like, Na-like, and Cu-like ions, where from the spectra of resonances very accurate values for energy splittings are derived for crucial tests of relativistic, correlation, and QED effects.     

Influence of the slow wave on the relation between the angular resonances and the leaky guided modes properties for a poroelastic plate embedded in water

A numerical study of the guided modes in a water-saturated poroelastic plate that obeys the Biot theory is presented. In the first part, we study the leaky guided modes and the angular resonances when the slow wave does not propagate. Two types of guided modes exist. The first ones occur from coupling of the fast longitudinal wave with the shear wave; most of them propagate whatever the frequency is, provided that it is not close to their cut-off frequencies. The leaky guided modes of the second type occur from coupling of the two longitudinal waves and the shear wave. These modes do not propagate (they are highly damped) as long as the slow wave remains diffusive. We show that the characteristics of the angular resonances can be linked to the leaky guided waves of the first type in the same way as for an elastic plate. The guided modes of the second type may not be associated to angular resonances. In the second part, we consider a thinner plate in a higher frequency range so that the slow wave can propagate. Once again its influence is studied both on the leaky guided modes and on the angular resonances.     

Electromagnetic Forces on Plasma Particles in the Presence of Resonant and Nonresonant Plasma Turbulence

Nonlinear forces on plasma particles in the presence of a test nonresonant wave and resonant plasma wave turbulence are calculated. The important feature of the considered nonlinear effect is that the forces due to the nonresonant test wave act on the plasma particles in the absence of linear and nonlinear resonances between the wave and the particles. Although in a closed plasma-wave system the process is balanced by the quasilinear interaction between the plasma resonant turbulence and plasma particles (leading to nonstationarity and inhomogeneity of the system), in open systems the effect can be significant.     

An overview of atomic and molecular processes in critical velocityionization

The authors present an overview of the time development of some atomic and molecular processes in critical ionization velocity (CIV). In the preonset stage, metastable states play an important role: they provide an energy pooling mechanism allowing low-energy electrons to participate in the ionization process; they may explain the low energy threshold was well as the fast time scale in the onset of CIV. For a sustaining CIV to occur, Townsend's criterion has to be satisfied. The kinetic energies of the neutrals are transformed to plasma wave energies via beam-plasma instabilities, and the plasma waves that heat the electron result in a tail formation. Excitation of neutrals with subsequent radiation is an important energy loss mechanism. Finite size also limits the instability growth rate. In the propagation of CIV, ion-molecule reactions and molecular dissociative recombination are important