Does Σ–Σ–α Form Quasi-Bound States?

For the Σ–Σ–α system we theoretically look into the possible existence of a quasi-bound state in the framework of Faddeev calculations. We are particularly interested in the state of total iso-spin T=2, because there is no strong conversion between Ξ–N–α and ${\Lambda-\Lambda-\alpha}$ . An analytic continuation using the point method is applied to search the eigenvalue in the complex energy plane. In our results the Σ–Σ–α three-body system has two quasi-bound states (J ^π  = 0⁺) where, depending on the potential parameters in the Nijmegen NSC97 model potential, the energy ranges between ?1.4 and ?2.4 MeV and the level width is about 0.4 MeV for the ground state. In addition, we obtained the excited state at ?0.15 MeV (width 4 MeV).     

Theoretical Study of Triatomic Systems Involving Helium Atoms

The triatomic ⁴He system and its isotopic species ${^4{\rm He}_2^3{\rm He}}$ are theoretically investigated. By adopting the best empirical helium interaction potentials, we calculate the bound state energy levels as well as the rates for the three-body recombination processes: ⁴He + ⁴He + ⁴He → ⁴ He₂ + ⁴He and ⁴He + ⁴He + ³He → ⁴He₂ + ³He. We consider not only zero total angular momentum J = 0 states, but also J > 0 states. We also extend our study to mixed helium-alkali triatomic systems, that is ⁴He₂ X with X = ⁷Li, ²³Na, ³⁹K, ⁸⁵ Rb, and ¹³³Cs. The energy levels of all the J ≥ 0 bound states for these species are calculated as well as the rates for three-body recombination processes such as ⁴He + ⁴He + ⁷Li → ⁴ He₂ + ⁷Li and ⁴He + ⁴He + ⁷Li → ⁴ He⁷Li + ⁴He. In our calculations, the adiabatic hyperspherical representation is employed but we also obtain preliminary results using the Gaussian expansion method.     

Coupling effects of resonant and discretized non-resonant continuum states in4He +6Li scattering at 10 MeV/A

Alpha- particle scattering from the resonant (3 ₁ ⁺ ) and non-resonant continuum states of⁶Li is studied at incident energy 10 MeV/A. Theα+d breakup continuum part within the excitation energyE _ex=1.475–2.475 MeV is discretized in two energy bins. Unlike the results at higher incident energies, here the coupled-channel calculations show significant breakup continuum coupling effects on the elastic and inelastic scattering. It is shown that even when the continuum-continuum coupling effects are strong, the experimental data of the ground state and the resonant as well as discretized non-resonant continuum states impose stringent constraint on the coupling strengths of the non-resonant continuum states.     

Study of Strangeness Photoproduction on the Neutron in the Threshold Region

Photoproduction of the neutral kaon on the deuteron has been investigated at the Research Center for Electron Photon Science, Tohoku University. We constructed the Neutral Kaon Spectrometer-2 for the detection of charged particles from the decay of the neutral kaon and the hyperon. We obtained a momentum distribution of K ⁰ with the inclusive measurement. It was consistent with the previous measurement. The total cross section of γ + d → K ⁰ + Λ + p was estimated from the measured integral cross section of γ + d → Λ + X. The total cross section with respect to the photon energy was compared with the theoretical calculations. It favored the Saclay-Lyon A model calculation with the ratio of the neutral to charged coupling constants of the axial-vector meson, K ₁, as ~ ?1.5. The energy dependence and the magnitude of the total cross section were similar to the total cross section of γ + p → K ⁺ Λ.     

Heavy ion e+e− pairs to all orders in Zα

The heavy ion cross section for continuum e⁺e^? pair production has been calculated to all orders in Zα. Comparison is made with available CERN SPS and RHIC STAR data. Computed cross sections are found to be reduced from perturbation theory with increasing charge of the colliding heavy ions and for all energy and momentum regions investigated. Au or Pb total cross sections are reduced by 28% (SPS), 17% (RHIC) and 11% (LHC). For very high energy (E _e ⁺, E _e ^?>3 GeV) forward pairs at LHC the reduction from perturbation theory is a bit larger (17%). Use of zero degree calorimeter triggering (and thus small impact parameter weighting) makes impact parameter representation of exact pair production useful. Preliminary exact calculations in the zero impact parameter limit show a much larger reduction from perturbation theory (about 40%) at both RHIC and LHC.     

Studies of Light Neutron-Excess Nuclei from Bounds to Continuum

The generalized two-center cluster model (GTCM), which can handle various single particle configurations in general two center systems, is applied to the light neutron-rich system, ¹² Be = α + α +4N. We discuss the change of the neutrons’ configuration around two α as a variation of an excitation energy. The covalent, ionic and atomic configurations coexists with the degenerate feature above the α +⁸ He _g.s. particle-decay threshold. We find the strong enhancement in the monopole excitation from the ground state to the excited states. The GTCM calculation is also applied to even Be isotopes, and the systematics on the structural changes from bound region to continuum is discussed.     

Two-state curve crossing processes involving rotational coupling in the Na 2 + molecular ion

We examine the relative utility of the Landau-Zener, phase integral, and semiclassical Magnus approximations for processes involving a real crossing of two potential curves. As an example we consider rotational coupling in Na ₂ ⁺ . Numerical calculations for the ¦3p〉→¦3s〉 quenching process and for ¦3p〉→¦3d〉 excitation agree well with recent experiments in the energy range 20 eV≦E_K≦50 eV. Simple expressions forS-matrix elements, differential and total cross sections in these approximations depend only on accurate evaluation of a few JWKB phases. For the total cross section further simplification of the Magnus results yields a useful semiempirical formula.     

Investigation of the mechanism of inelastic alpha-particle scattering on 28Si nuclei by the method of angular αγ correlations at E α = 30.3 MeV

The angular dependence of the differential cross sections for alpha-particle scattering on ²⁸Si nuclei and double-differential cross sections for the reaction ²⁸Si(α, αγ)²⁸Si at E _α = 30.3 MeV is measured for the case of alpha-particle emission angle between 20° and 160° and the excitation of low-lying states of the ²⁸Si nucleus (0⁺, ground state; 2⁺ state at 1.78 MeV; 4⁺ state at 4.62 MeV; 0⁺ state at 4.96 MeV; and 3^? + 4⁺, 6.88 MeV + 6.89 MeV). The spin-tensor components of the density matrix for the 2⁺ state at 1.78 MeV and the 4⁺ state at 4.62 MeV in the ²⁸Si* nucleus are reconstructed in a modelindependent way. Seven rank-6 components are reconstructed for the 3^? state at 6.88 MeV. Orientation features of ²⁸Si* are determined. The experimental data in question are compared with the results of the calculations performed under the assumption of the collective-excitation mechanism and by the coupled-channel method.     

High-twist correction for inclusive hadron production in photon-photon collisions

The contribution of the QCD high-twist subprocess γq→πq′ to the inclusive cross section for e⁺ e^? → e⁺ e^? + π^± + X is calculated both in the PETRA/PEP and the LEP energy range, in the equivalent-photon approximation. Superposed on the Born cross section and its O(α_s) correction, it gives agreement with the data at relatively low transverse momenta. It is suggested that this high-twist contribution may be further isolated experimentally by triggering simultaneously on both a fast hadron and the opposite-side jet.     

The ΔTz = + 1 Gamow-Teller excitation of N = 28 isotones

Results of shell-model calculations of Gamow-Teller strength distributions are presented for ⁵⁰Ti → ⁵⁰Sc, ⁵²Cr → ⁵²V and ⁵⁴Fe → ⁵⁴Mn. The results support the previous shell-model estimates that a large fraction of Gamow-Teller strength is concentrated at low excitation energy in the daughter nuclei. The strength distributions are in fairly good agreement with those of forward-angle cross sections of T₀ + 1 isospin states of the intermediate-energy (p, p') reaction on N = 28 isotones. An estimate of quenching in the T₀ → T₀ + 1 τσ mode transition is attempted. Calculations are performed also for the first 2⁺ and 4⁺ parent states in the context of electron capture at the late stages of stellar evolution.     

The structure ofT=1 levels inA=14 nuclei

States in¹⁴C, populated via the¹¹B(α, p) reaction at 14 MeV bombarding energy, were investigated with the Doppler Shift Attenuation Method (DSAM). The analysis ofpγ coincidence spectra taken in a Ge(Li) detector at 0? and 120? with the particle detector near 0? with respect to the beam direction yielded the following lifetimes and lifetime limits for the states at 6.09, 6.59, 7.01 and 7.34 MeV, respectively, <20 fs, <1,200 fs, <7 fs and 160±60 fs. Shell model calculations using the MSDI and an empirical interaction fitted to nuclear states in 1p and 2s 1d shell nuclei, are shown to account very well for the experimental levels andγ-transition rates of 5 different multipolarities. The structure of the (J ^*,T)=(2⁺, 1) levels is discussed in the light of the experimentally observed T_z-dependence of the 2⁺, 1→0⁺, 1E2 matrix elements.     

Mechanisms in d + 6Li three-body reactions at low bombarding energies

The three-body reactions induced by low energy deuterons on ⁶Li have been studied. The contributions from the sequential processes through the excited states of the intermediate ⁴He, ⁵Li, ⁶Li and ⁷Li nuclei dominate the coincidence spectra. The quasi-free d + d → d + d, d + α → d + α, and d + d → p + t reactions have been observed and compared with plane wave impulse approximation (PWIA) calculations.     

Alpha induced reactions

A comprehensive model forα particle induced reactions, recently proposed by two of the authors, has been improved and utilised in the analysis of proton andα particle spectra, angular distributions, excitation functions, spectra of neutrons emitted in the decay of continuum states on nuclei with 50<A<230 atα energies varying from 50 to 160 MeV. A unique set of average parameters has been used in all the calculations. Most of them were the same utilised in previous analyses of nucleon andπ ^? induced reactions. The energy and mass dependence (which turns out to be quite weak) of the additional parameters which are needed to describe theα particle induced reactions has been determined. The comparison with experimental data shows that the model discussed allows one to reproduce successfully the cross sections ofα particle induced reactions with an accuracy comparable to the one already gained in the analysis of nucleon andπ ^? reactions with the Exciton Model.     

Deformed states of high spin in42Ca

The⁴²Ca levels at 4,715 and 6,633 keV excitation energy have been investigated using the³⁹ K(α,pγ reaction atE _α=14 and 15 MeV. From particle-γ-ray angular correlations the spin assignmentsJ(4,715)=6, 4 andJ(6,633)=8, 6, 4 have been obtained. Lifetime measurements using the Doppler-shift attenuation method yieldedτ (4,715)=120±46 fs andτ(6,633)=52±21 fs. Both levels have positive parity and decay by enhancedE2 transitions. They are interpreted as theJ ^π=6⁺ and 8⁺ members, respectively, of theK ^π=0⁺ rotational band which has theE _x =1,837, 2,423 and 3,250 keV states as further members. The enhancement of inbandE2 transitions is 50 _?16 ⁺³⁵ W.u. (6→4) and 63 W.u. (8→6) respectively. The intrinsic quadrupole moments which have been derived on the basis of the coexistence model, areQ ₀=1.13?0.16/+0.37b(8→6) andQ ₀=1.36±0.25b(6→4), respectively. TheJ ^π=10⁺ member of the rotational band has possibly been observed as a level at 8,856±5 keV excitation energy.     

Measurement of the 2H(p,n) Breakup Reaction at 170 MeV and the Three-Nucleon Force Effects

The effects of three nucleon force (3NF) have been actively studied via the nucleon–deuteron (Nd) scattering states. The differential cross sections and the vector analyzing powers A _y of the ²H(p, n) inclusive breakup reaction at 170 MeV were measured for the study of 3NF effects in the intermediate energy region. The polarized proton beam of 170 MeV was injected to the deuterated polyethylene (CD₂) target and the energy of scattered neutrons were measured by using TOF method. The data were compared with the Faddeev calculations based on modern nucleon–nucleon (NN) forces with and without the 3NF. Concerning the differential cross sections, we can see large discrepancies between the data and the calculations in the region of scattered neutron energies are low, which is similar to the results of the ²H(p, p) inclusive breakup reaction at 250 MeV.     

Time-dependent quantum wave packet and quasiclassical trajectory studies of the Au(2S) + H2(X1∑+g) → AuH(X1∑+g) + H(2S) reaction

The time-dependent quantum wave packet (TDWP) and quasiclassical trajectory calculations (QCT) are carried out for the Au(²S) + H₂(X¹∑⁺_g) → AuH(X¹∑⁺_g) + H(²S) reaction on a global potential energy surface. The reaction probabilities at a series of J values, integral cross sections (ICSs) and differential cross sections of the title reaction are calculated by the TDWP method. For reaction probabilities, there are a mass of sharp oscillations at low collision energy, which can be attributed to resonances supported by the potential well. Due to the endothermicity of the title reaction, the total ICS shows a threshold about 1.53 eV. In order to further investigate the reactive mechanism, the lifetime of complex is calculated by QCT method. At the low collision energy, most intermediate complexes are long lived, which implies that the reaction is governed by indirect reactive mechanism. With the collision energy increasing, the direct reactive mechanism occupies the dominant position. Due to the change of the reactive mechanism, the angular distribution shifts toward the forward direction with collision energy increasing. The isotopic variant, Au + D₂→AuD + D reaction, is also calculated by TDWP method. The calculated reaction probabilities and ICSs show that the isotope effect reduces the reactivity.     

K*0Σ+ Photoproduction from Threshold to 3.0 GeV

The CLAS collaboration and the CBELSA/TAPS collaboration reported the differential cross section data for K*⁰ photoproduction, and found that the t-channel K exchange dominates the production amplitudes at small scattering angles. The measurement of forward-angle parity spin asymmetry for the γ p → K*⁰Σ⁺ reaction, where the theoretical calculations show an unambiguous signal, would establish the role of the κ(800). The γ p → K*⁰Σ⁺ reaction, where the Σ⁺ was identified through missing mass, on a liquid hydrogen target was measured at the LEPS detector in the energy from threshold to 3.0 GeV by using a linearly polarized photon beam at SPring-8. Decay angular distributions in the rest frame of the K ⁺ π ^? system were fit to extract spin-density matrix elements of the K*⁰ decay.     

A microscopic model for the pd → tπ+ reaction

A microscopic model for the pd → tπ⁺ reaction is constructed using two-body isobar wave functions containing the Δ(1236). This model results in an analytical form for the reaction cross section and so it is possible to check the validity of those more approximate models that relate the pd → tπ⁺ cross section to the pp → dπ⁺ cross section. The calculations are performed at the three proton lab energies of 400, 470 and 600 MeV.     

16O, 24, 26Mg, 28Si, 32S, 40Ca(α, 12C) and multi-α-cluster transfer reactions

The (α, ¹²C) reaction has been studied on a variety of nuclei, A = 16 to 40, at E_α = 90.3 MeV. The data indicate a rapid fall-off of cross sections with increasing target mass, approximately as A_t^{?5 ± 1}. This and other systematics are used to estimate cross sections for multi-α-cluster transfer reactions in heavy nuclei and suggest σ_T < 10^?34 cm² consistent with present experimental limits. The data for ²⁴Mg(α, ¹²C)¹⁶O has been studied in more detail and indicates a selective population of final states including ¹⁶O g.s., with oscillatory angular distributions in some instances. Finite-range distorted-wave Born approximation calculations for direct ⁸Be pickup have been performed utilizing cluster overlap amplitudes obtained with zero-order SU(3) wave functions. The calculations are in qualitative, and often quantitative, agreement with shapes and absolute magnitudes of the measured angular distributions although the cross sections for certain α-cluster states (2⁺, E_x ≈ 7 MeV; 4⁺, E_x ≈ 10.3 MeV) are greatly overestimated with this model. Other more complicated mechanisms, such as successive α-transfer, cannot be excluded. The systematics of the calculated ⁸Be cluster overlaps and the calculated and measured (α, ¹²C) cross sections are investigated, and implications for multi-α-cluster transfer reactions are discussed.     

Coupling effects of resonant and discretized non-resonant continuum states in 4He + 6Li scattering at 10 MeV/A

Alpha-particle scattering from the resonant (3 ₁ ⁺ ) and non-resonant continuum states of ⁶Li is studied at incident energy 10 MeV/A. The α + d breakup continuum part within the excitation energy E _ex = 1.475–2.475 MeV is discretized in two energy bins. Unlike the results at higher incident energies, here the coupled-channel calculations show significant breakup continuum coupling effects on the elastic and inelastic scattering. It is shown that even when the continuum-continuum coupling effects are strong, the experimental data of the ground state and the resonant as well as discretized non-resonant continuum states impose stringent constraint on the coupling strengths of the non-resonant continuum states.