Two photons into π<Superscript>0</Superscript>π<Superscript>0</Superscript>

We perform a theoretical study based on dispersion relations of the reaction γγ → π ⁰ π ⁰ emphasizing the low-energy region. We discuss how the ƒ ⁰(980) signal emerges in γγ → ππ within the dispersive approach and how this fixes to a large extent the phase of the isoscalar S-wave γγ → ππ amplitude above the threshold. This allows us to make sharper predictions for the cross-section at lower energies and our results could then be used to distinguish between different ππ isoscalar S-wave parameterizations with the advent of new precise data on ππ → π ⁰ π ⁰. We compare our dispersive approach with an updated calculation employing the unitary chiral perturbation theory (U _gC PT). We also pay special attention to the role played by the σ-resonance in γγ → ππ and calculate its coupling and width to γγ, for which we obtain Γ(σ → γγ) = (1.68 ± 0.15) keV.     

<Emphasis Type="Italic">J</Emphasis><Superscript>π</Superscript>0<Superscript>−</Superscript> levels in <Superscript>156</Superscript>Gd and <Superscript>158</Superscript>Gd

The 0^? states in the ¹⁵⁶Gd nucleus at E = 1952.38 keV and in the ¹⁵⁸Gd nucleus at E = 2269.16 keV are established on the basis of an analysis of available data on even-even deformed nuclei. From data on the deexcitation of the levels and on the probability of their population by beta transitions, it is found that these states have a two-particle proton structure. A comparison of our data with information about the 0^? levels in the ¹⁷⁰Yb and ¹⁷⁶Hf nuclei makes it possible to conclude that J^π0^? two-particle states exist at an excitation energy of about 2 MeV and higher.     

The evaluation of the branching ratios of the decays φ(1020)→2π<Superscript>+</Superscript>2π<Superscript>−</Superscript>π<Superscript>0</Superscript>, π<Superscript>+</Superscript>π<Superscript>−</Superscript>3π<Superscript>0</Superscript>

Combining the Okubo-Zweig-Iizuka rule in the decay φ→ρπ→π⁺π^?π⁰ with the ρ→4π decay amplitudes, we calculate the φ→2π⁺2π^?π⁰ and φ→π⁺π^?3π⁰ ones. The partial widths of the above φ decays are evaluated, and the excitation curves in e⁺e^? annihilation are obtained, assuming reasonable particular relations among the parameters characterizing the anomalous terms of the HLS Lagrangian. The evaluated branching ratios B_φ→π⁺_π^?_3π⁰ ≈ 2 × 10^?7 and B_φ→2π⁺_2π^?_π⁰ ≈ 7 × 10^?7 are such that, with the luminosity L=500 pb^?1 attained at DAΦNE φ factory, one may already possess about 1685 events of the decays φ→5π.     

Exclusive ωπ<Superscript>0</Superscript> production with muons<Superscript>⋆</Superscript>

Using 160GeV muon scattering data collected with the COMPASS experiment at CERN, the exclusive production of ωπ⁰ via virtual photons was studied. Selective population of a peak around 1250MeV is observed. Possible contributions from spin-parity 1^- are searched for, inspecting decay angular correlations. In particular, the orientation of the ω decay plane may allow a distinction from the 1⁺ b ₁(1235) state. Our observation is compared with indications of a (1250) in annihilation and in γp . Original article based on material presented at HADRON 2007.     

<Superscript>16</Superscript>O/<Superscript>18</Superscript>O oxygen isotope exchange kinetics in MnO<Stack><Subscript>4</Subscript><Superscript>−</Superscript></Stack> as probed by <Superscript>55</Superscript>Mn NMR

The effect of the ¹⁶O ? ¹⁸O substitution in the coordination sphere of permanganate anion MnO ₄ ^? on the chemical shift of ⁵⁵Mn nuclei have been studied by ¹⁷O and ⁵⁵Mn NMR. Time constants τ _n,k of oxygen exchange in the water–permanganate anion system have been estimated. In nearly neutral solutions (pH ≈ 6.8–7.2), the oxygen exchange time is on the order of tens of hours. Bubbling gaseous HCl through this solution for a few seconds leads to the equilibrium distribution of oxygen isotopes in the manganese coordination sphere. The observed temperature dependences of isotope-induced ⁵⁵Mn NMR shifts in Mn¹⁶ O _44-n ¹⁸ O _n ^– (n = 0–4) have been treated as a result of rovibrational averaging of Mn–O bond lengths. The change in the Mn—O bond length in caused by the ¹⁶O → ¹⁸O isotope substitution is on the order of 10^–4 Å.     

Processes e<Superscript>+</Superscript>e<Superscript>−</Superscript> → π<Superscript>0</Superscript>(π<Superscript>0</Superscript>′) γ in extended NJL model

The processes of electron-positron annihilation into π⁰γ and into π′(1300)γ are considered within an extended NJL model. The intermediate vector mesons ρ ⁰, ω ρ′(1450), and ω(1420) are taken into account. The latter two mesons are treated as the first radial excited states. They are incorporated into the NJL model by means of a polynomial form factor. Numerical predictions for the cross-sections of these processes are received for the center-of-mass energies below 2 GeV. Our results for the π⁰γ production are in agreement with experimental data obtained in the energy region 600–1020 MeV.     

Potential energy of <Superscript>∞</Superscript>H<Stack><Subscript>2</Subscript><Superscript>-</Superscript></Stack>(<Superscript>2</Superscript>∑<Stack><Subscript>u</Subscript><Superscript>+</Superscript></Stack> in the bound-state region

An accurate calculation of the lowest negative electronic state of H ₂ ^- (fixed nuclei) is reported using the CCSD(T) method and doubly augmented cc-pv5z basis set. Comparison has been made with the reference data by Senekowitsch et al. [Chem. Phys. Lett. 111 (1984) 211]. Owing to larger size of the basisset and inclusion of triple excitations, no vertical shift in this work is necessary to reproduce the asymptotics of H + H ^-. In addition, the effect of basis-set truncation is estimated, based on the complete-basis-set extrapolation method. The contribution of correlated electron-proton motion to the electron-energy curve for H₂ ^– dynamics is pointed out.Dedicated to Prof. Jií Horáek on the occasion of his 60th birthday.     

Inversion of the <Emphasis Type="Italic">K</Emphasis><Superscript>π</Superscript>=1<Superscript>−</Superscript> states in <Superscript>156</Superscript>Gd and <Superscript>170</Superscript>Yb

For the ¹⁵⁶Gd and ¹⁷⁰Yb nuclei, where the inversion of levels in the K^π=1^? bands is observed, the energies of rotational levels are calculated on the basis of the Coriolis interaction model for the states of two bands whose quantum numbers are K^π=1^?. New 0^? levels are introduced in ¹⁷⁰Yb, and the structure of ¹⁷⁰Er is refined. The interaction parameters calculated for six nuclei are considered within the structure predicted by the quasiparticle-phonon model.     

Two-neutrino positron double-beta decay of <Superscript>106</Superscript>Cd for the 0<Superscript>+</Superscript> → 0<Superscript>+</Superscript> transition

The two-neutrino positron double-beta decay of ¹⁰⁶Cd for the 0 ⁺ 0⁺ transition has been studied in the Hartree-Fock-Bogoliubov model in conjunction with the summation method. In the first step, the reliability of the intrinsic wave functions of ¹⁰⁶Cd and ¹⁰⁶Pd nuclei has been tested by comparing the theoretically calculated results for yrast spectra, reduced B(E2: 0⁺ 2⁺) transition probabilities, quadrupole moments Q(2⁺) and gyromagnetic factors g(2⁺) with the available experimental data. In the second step, the nuclear transition matrix element M₂ and the half-life T_1/2² for the 0 ⁺ 0⁺ transition have been calculated with these wave functions. Moreover, we have studied the effect of deformation on the nuclear transition matrix element M₂.     

Decays of baryon resonances into ΛK<Superscript>+</Superscript>, ΣK<Superscript>+</Superscript> and Σ<Superscript>+</Superscript>K<Superscript>0</Superscript>

Cross-sections, beam asymmetries, and recoil polarisations for the reactions γp → K ⁺Λ;γp → K ⁺Σ⁰, and γp → K ⁰Σ⁺ have been measured by the SAPHIR, CLAS, and LEPS Collaborations with high statistics and good angular coverage for centre-of-mass energies between 1.6 and 2.3 GeV. The combined analysis of these data with data from π and η photoproduction reveals evidence for new baryon resonances in this energy region. A new P₁₁ state with mass 1840 MeV and width 140 MeV was observed contributing to most of the fitted reactions. The data demand the presence of two D₁₃ states at 1875 and, optimistically, at 2170 MeV.     

Gamow-Teller 1<Superscript>+</Superscript> states in <Superscript>112–124</Superscript>Sb isotopes

The violated supersymmetry property of the pairing interaction between nucleons were restored using the Pyatov method [Pyatov and Salamov, Nucleonica 22, 127 (1977)]. The eigenvalues and eigenfunctions of the restored Hamiltonian with the separable residual Gamow-Teller effective interactions in the particle-hole and particle-particle channels were solved within the framework of proton-neutron quasirandom phase approximation (pnQRPA). The Gamow-Teller resonance energies for ^112–124Sb isotopes and the differential cross-sections for Sn(³He, t)Sb reactions at E(³He) = 200 MeV occurring by the excitation of the Gamow-Teller resonance state were calculated. The calculated values were compared with other calculations and the corresponding experimental data.     

Production of residual radioactive nuclei in thin <Superscript>209</Superscript>Bi, <Superscript>nat</Superscript>Pb, <Superscript>206</Superscript>Pb, <Superscript>207</Superscript>Pb,and <Superscript>208</Superscript>Pb targets bombarded with 0.04–2.6 GeV protons

The results of the experimental measurement and numerical simulation of the cross sections for residual radioactive nuclei production in thin ²⁰⁹Bi, ^natPb, ²⁰⁶Pb, ²⁰⁷Pb, and ²⁰⁸Pb targets bombarded with protons in the energy range from 0.04 to 2.6 GeV are reported. The nuclide production cross sections were measured using γ spectrometry with a high-resolution Ge detector. The experimental data include a total of 5972 reaction cross sections at 11 proton energy values. The results are compared to the data from other laboratories reported in 80 papers. The model calculations were carried out using eight simulation code packages: LAHET, INCL4 + ABLA, CEM03, LAQGSM + GEM2, CASCADE, CASCADE-2004, CASCADO, and LAHETO. A detailed analysis of discrepancies between the measured and calculated data is presented.     

Study of ground states of <Superscript>3</Superscript>H, <Superscript>3,4,6</Superscript>He, <Superscript>6</Superscript>Li,and <Superscript>9</Superscript>Be nuclei by Feynman’s continual integrals method

The ground-state energies and the squared moduli of the ground-state wave functions are calculated for the ³H, ^3,4,6He, ⁶Li, and ⁹Be nuclei by Feynman’s continual (path) integrals method. The results are in satisfactory agreement with experimental data.     

Conserved vector current and decays τ<Superscript>−</Superscript> → η(η′)π<Superscript>−</Superscript>π<Superscript>0</Superscript>ν<Subscript>τ</Subscript>

We use experimental data on e ⁺ e ^? → (η′)π⁺π^? and conservation of vector current to estimate the branching fractions of τ^? decay to η(η′)π^?π⁰ν_τ. The obtained values are compared to the experimental results.     

Long <Emphasis FontCategory="NonProportional">K</Emphasis><Superscript>π</Superscript> = 0<Superscript>+</Superscript> and 4<Superscript>−</Superscript> bands in deformed nuclei

Experimental data on some long bands in N=88–98 deformed nuclei are analyzed on the basis of a method systematizing the energies of levels and inertial parameters and a method employing the analogy between neighboring. Beta bands built on low-lying 0 ₂ ⁺ levels are identified in N=90 isotones, including the ¹⁵⁸Er, ¹⁶⁰Yb, and ¹⁶²Hf nuclei. Some of intermediate members of these bands have not been found yet. The systematic properties of 4^? bands are presented, and the dynamics of the inertial parameters of these bands in N=88–98 isotones is revealed. The bands are identified in ¹⁵⁸Yb, ¹⁵⁶Dy, ¹⁵⁶Er, ¹⁶²Yb, and ¹⁶⁶Hf.     

Emission spectroscopy of the A<Superscript>1</Superscript>Π–X<Superscript>1</Superscript>Σ<Superscript>+</Superscript> system of AlH

The high-resolution emission spectrum of the A¹ Π–X¹Σ⁺ transition of AlH was observed in the 18 000–25 000 cm^-1 spectral region using a conventional spectroscopic technique. The AlH molecules were excited in an Al hollow-cathode lamp filled with a mixture of Ne carried gas and a trace amount of NH₃. The emission from the discharge was observed with a plane grating spectrograph and recorded by a photomultiplier tube. In total 163 transition wave numbers belonging to six bands (0-0,1 and 1-0,1,2,3) were precisely measured and rotationally analysed. In the final fit the present data have been combined with available high-resolution measurements of the vibration-rotation bands by White et al. [J. Chem. Phys. 99, 8371 (1993)]. This procedure enabled extracting molecular constants for the A¹ Π and X¹ Σ⁺ states of AlH. A very slight local perturbation has been discovered in the v=1 vibration level of the A¹ Π state at J=5. This was probably caused by the interaction with the a³Π state.     

Photoproduction of π<Superscript>0</Superscript>π<Superscript>+</Superscript> pairs on proton and deuteron

The reaction of π⁰π⁺ photoproduction on free and quasi-free protons with γ-ray energies from 0.5 to 1.5 GeV has been studied. Its cross section was measured in the range θ _π ⁰ ≥ 20°. The distributions of π⁰π⁺, π⁰n, and π⁺n invariant masses were analyzed. The experiment was performed using the Compton back-scattered γ-ray beam at the GRAAL facility (Grenoble, France), applying liquid deuterium and hydrogen targets and a large-aperture (almost 4π) detector. Particular attention was paid to analysis of systematic errors related to the neutron detection efficiency.     

Detailed Investigations of Neutron–Neutron Angular Correlations in Slow-Neutron-Induced Fission of <Superscript>233</Superscript>U, <Superscript>235</Superscript>U,and <Superscript>239</Superscript>Pu

An experiment devoted to studying neutron–neutron angular correlations in the slow-neutroninduced fission of ²³³U, ²³⁵U and ²³⁹Pu nuclei was performed. The experimentally determined angular dependence of the number of neutron–neutron coincidences was compared with the results of a Monte Carlo simulation for various values of the neutron-detection threshold in the range between 490 and 2080 keV. It was found that the experimental angular distributions in question can be described well under the assumption that 2% to 5% of all prompt fission neutrons are emitted isotropically in the laboratory frame. Probably, such neutrons can be interpreted as so-called scission neutrons directly associated with the nuclear-rupture instant. Energy distributions of this component were also obtained from the present analysis.     

Cross sections for the photofission of <Superscript>243</Superscript>Cm, <Superscript>245</Superscript>Cm, <Superscript>249</Superscript>Bk,and <Superscript>249</Superscript>Cf isotopes in the energy range from the threshold to 10–12 MeV

The relative method was used to measure the photofission cross sections for ²⁴³Cm and ²⁴⁹Cf isotopes in the energy range from 6 to 12 MeV, for ²⁴⁵Cm in the energy range from 5 to 10 MeV, and for ²⁴⁹Bk in the energy range from 5.5 to 10 MeV. The measurements were performed with an energy step of 50 to 200 keV by using the microtron installed at the Institute of Physics and Power Engineering (Obninsk). The cross section for ²³⁸U photofission was used as a reference in these measurements. Data on the cross sections for ²⁴³Cm, ²⁴⁵Cm, and ²⁴⁹Bk photofission were obtained for the first time, while data on the cross section for ²⁴⁹Cf photofission were obtained for the first time only in the energyregion E<10 MeV. The data on the ²⁴⁵Cm nucleus suggest that, in the energy region around 6 MeV, the cross section for its photofission has a maximum, which is likely to be due to the low-energy resonance structure of the dipole-photoabsorption cross section. For ²⁴⁹Cf, an anomalously large value of the photo fission cross section is observed in the region of the first maximum of the giant dipole resonance (E≈11 MeV). By comparing the energy dependences obtained for the fissilities of the ²⁴³Cm and ²⁴⁹Bk isotopes from photofission data with the fissilities from direct-reaction data, it is found that the observed fission thresholds agree and that there is a plateau-like dependence at energies above 7.5 MeV. For the ²⁴⁵Cm and ²⁴⁹Cf nuclei, there are no similar data for performing such a comparison. Data on the fissilities as obtained from the present series of relative measurements that employ the microtron bremsstrahlung spectrum are analyzed.     

(EC + β<Superscript>+</Superscript>) decays of the 11/2<Superscript>-</Superscript> isomer and 1/2<Superscript>+</Superscript> ground state of <Superscript>143</Superscript>Dy

The 1/2⁺ ground state and a 11/2^- isomer of very neutron-deficient isotope ¹⁴³Dy were produced by irradiation of an enriched target of ¹⁰⁶Cd with ⁴⁰Ca and studied by using a helium-jet fast tape-transport system in combination with proton-γ, X-γ and γ-γ coincidence measurements. A simple ( EC + β⁺) decay scheme of ^143mDy with a half-life of 3.0(3) s and a tentative ( EC + β⁺) decay scheme of ^143gDy with a half-life of 5.6(10) s are proposed. As a by-product, the 347- and 545-keV γ transitions in ¹³⁸Sm following the β-delayed proton emission of ¹³⁹Gd decay and the 323-keV γ transition in ¹³⁹Eu following the β-delayed proton emission of ¹⁴⁰Tb decay could be observed for the first time. Received: 20 August 2002 / Accepted: 28 October 2002 / Published online: 11 February 2003 RID="a" ID="a"e-mail: xsw@ns.lzb.ac.cn Communicated by D. Schwalm