On the quark structure of the lightest nuclei

It is shown that in the 9q- and 12q-systems, i.e.,³He-³He and⁴He nuclei, the most energetically favourable colour magnetic types of symmetry are [f]_cs=[621] and [f]_cs=[82²], which corresponds to the orbital configurationsS ⁵ P ⁴ [52²] _X andS ⁶ P ⁶ [62³] _X . The colour magnetic nucleon attraction associated with these configurations increases as the square of the nucleon number in the sequence²H,³He,⁴He, becoming quite strong in⁴He. This may provide a basis for explaining the “mysterious properties” of³He-³He and⁴He. However, with the further increase in A, the above effect drastically decreases. A qualitative calculation on the quark excitation spectrum for the³H-³He and⁴He nuclei is presented. The⁴He nucleus seems to possess some properties of a “quark magic nucleus”. The experimental situation is discussed.     

A measurement of the electromagnetic form factor of the eta meson and of the branching ratio for the eta Dalitz decay

In an optical spark chamber experiment we have obtained a sample of 80 eta Dalitz decays (η → e⁺e^?γ) and have measured the eta electromagnetic form factor to be F(X) = 1.0?(0.22 ±0.45)X, where X=M_ee²/M_η², and the branching ratio (η→e⁺e^?γ/(η→π⁺π^?π⁰)= (0.0082 ± 0.0020).     

Hyperfine anomaly in the spectrum of the osmium atom. effect of the spatial distribution of nuclear charge

Contributions of the superposition of configurations ns ²5d ⁸+ns5d ⁸ n′s (n=1–5, n′=6–10) and ns ²5d ⁶+ns5d ⁶ n′s (n=1–6, n′=7–10) to parameters a _5d ⁰¹ , a _5d ¹² , and a _5d ¹⁰ of the hyperfine structure in the spectrum of the osmium atom OsI are calculated. It is shown that the nonzero contribution is made only to a _5d ¹⁰ . The effect of the spatial distribution of nuclear charge on the parameters of the hyperfine structure in the spectra of ¹⁸⁷Os and ¹⁸⁹Os isotopes and on the hyperfine anomaly for the 5d ⁷6s levels in the spectrum of these isotopes is estimated.     

Phenomenology of Σ+→pℓ+ℓ− and the structure of the weak non-leptonic Hamiltonian

The problem of the radiative non-leptonic weak baryon decays is reviewed in light of the new experimental findings. With the aim of exploring the structure of the weak non-leptonic Hamiltonian, we present a detailed phenomenological analysis of Σ⁺→p?⁺?^? transitions. Lower and upper limits for rates derivable with standard physics are determined as Γ(Σ⁺→pe ⁺ e ^?)/Σ⁺→pγ)≧7.2×10^?3 and 1/1210? Γ(Σ⁺→pe ⁺ e ⁺)/Γ(Σ⁺→pe ⁺ e ^?)?1/120. From existing data on Σ⁺→pe ⁺ e ^? we obtain limits on the values of the charge radius form factors |c ₁/b ₁|?5;|c ₂/b ₁|? 10, where the magnetic form factor is given by the Σ⁺→dγ, decay asb ₁(0)= 6.9±0.9 MeV. The short distance contribution of the QCD corrected single quarks→dλ transition is shown not to play a dominant role in these decays.     

Direct measurement of the lifetime of the neutral pion

The lifetime of the neutral pion (π⁰) has been directly measured. The lifetime has been found to be τ_π⁰ = (0.897±0.022±0.017) × 10^?16 s. The systematic error results from uncertainties in the momentum spectrum of the π⁰ used for the measurement. This measurement yields a decay width of the π⁰ of (7.34±0.18±0.11) eV. An axial anomaly calculation, which neglects the finite mass of the π⁰, predicts a value of 7.87 eV.     

Validity of the equivalent-photon approximation for the production of massive spin-1 particles

We point out that the equivalent-photon approximation (EPA) for processes with massive spin-1 particles in the final state would have validity in a more restricted kinematic domain than for processes where it is commonly applied, viz., those with spin-1/2 or spin-0 particles in the final state. We obtain the criterion for the validity ofEPA for the two-photon production of a pair of charged, massive, point-like spin-1 particlesV ^±, each of massM and with a standard magnetic moment (κ=1). In a process in which one of the photons is real and the other virtual with four-momentumq, the condition for the validity ofEPA is |q ²|≪M ², in addition to the usual condition |q ²|≪W ²,W being theV ⁺ V ⁻ invariant mass. In a process in which both photons are virtual (with four-momentaq andq′), our condition is |q ²||q′²|W ⁴ ≪ 16M ⁸, in addition to |q ²| ≪M ², |q′²| ≪M ² and |q ²| ≪W ², |q′²| ≪W ². Even when these extra conditions permitting the use ofEPA are not fulfilled, convenient approximate expressions may still be obtained assuming merely |q ²| ≪W ² and |q′²| ≪W ². We also discuss how the extra conditions are altered when the vector bosons are incorporated in a spontaneously broken gauge theory. Examples ofW boson production in Weinberg-Salam model are considered for which the condition |q ²||q′²|W ⁴ ≪ 16M ⁸ is shown to be removed.     

Study of the excited states of119Sn by the decay of119g+m In

The decay of^119g+m In to the excited states of¹¹⁹Sn was investigated.¹¹⁹In was produced by the¹²⁰Sn(γ,p)¹¹⁹In reaction on an enriched SnO₂ target. The isomeric transition of 311.25 keV to the¹¹⁹In ground state was observed. In the beta decay of^119m In excited states at 23.9, 920.5, 921.4, 1089.0, 1187.9 and 1249.6keV in¹¹⁹Sn withJ ^π values of 3/2⁺, 3/2⁺, 5/2⁺, 5/2⁺, 3/2⁺ and 1/2⁺ respectively, are fed. In the decay of the¹¹⁹In ground state only the 7/2⁺ level in¹¹⁹Sn at 787.0 keV is fed.     

Measurement of the g-Factor of the 27− High-Spin Isomer State of 152Dy

The g-factor of the 27⁻ isomer state of ¹⁵²Dy has been measured using the Time-Integral Perturbed Angular Distribution (TIPAD) method. The high-spin states of ¹⁵²Dy have been populated by ¹⁴¹Pr(¹⁶O,p4n)¹⁵²Dy reaction at E = 115 MeV from the AVF cyclotron at CYRIC. The paramagnetic correction factor of Dy ions in Pr has been determined to be 4.2(5) by the Time-Differential Perturbed Angular Distribution (TDPAD) measurement of the 21⁻ state of ¹⁵²Dy. As a result, the g-factor of the 27⁻ isomer state of ¹⁵²Dy has been obtained to be +0.09(5). This shows the smaller value than the expected one of +0.39 deduced from a fully aligned configuration of π(h _11/2 ²) ⊗ ν(f _7/2 ² h _9/2 i _13/2).     

Screening effect of the coulomb interaction on the energy levels of atomic and molecular systems

The energies of atomic and molecular systems with a screened Coulomb interaction are expressed in terms of properties of the system with a conventional Coulomb interaction to the third order in the screening constant. The energy levels of an H atom, an H^? ion, and nonadiabatic systems, namely, the positronium ion e ⁺ e ^? e ^? and the positronium molecule e ⁺ e ⁺ e ^? e ^?, are calculated for screened Coulomb interactions of charged particles. It is demonstrated that, as the screening constant of the Coulomb interaction increases, the stability of the hydrogen atom, the H^? ion, and the positronium molecule e ⁺ e ⁺ e ^? e ^? decreases, whereas the stability of the positronium ion e ⁺ e ^? e ^? increases after a slight decrease.     

Effect of the Structure of Light Loosely Bound Nuclei on the Mechanisms of Nuclear Reactions

The results of experiments devoted to studying fusion and transfer reactions in beams of loosely bound (³He) and cluster (⁶Li, ⁷Li) nuclei, as well as nuclei that have a halo structure (⁶He and ⁸He), with nuclei of light and heavy elements are generalized. Special features in the behavior of cross sections for the formation of evaporation residues and transfer-reaction products at energies near the barrier are revealed. The behavior of cross sections for nucleon- and cluster-transfer reactions leads to different populations of single-particle and collective states in target-like nuclei. The effect of various channels of nuclear reactions involving light nuclei on the population of the ^195mHg and ^197mHg(13/2⁺), ^198mTl and ^196mTl(7⁺), and ^196mAu and ^198mAu(12⁻) pairs of isomeric states is considered. The values of the isomeric ratios (σ_m/σ_g) for reaction products originating from fusion reactions followed by particle evaporation and from nucleon-and cluster-transfer reactions are explained.

     

A determination of the total width of the ϒ(9.46) meson

Using the DASP detector at the DESY storage ring DORIS we have continued measuring e⁺e^? annihilations near and on the ?(9.46) resonance. From the cross sections for e⁺e^? → μ⁺μ^? and e⁺e^? → hadrons we obtain a μ⁺μ^? branching ratio for the ?(9.46) of (2.9 ± 1.3 ± 0.5) %, a leptonic width $\text{г}{}_{\mathrm{<mtext>ee</mtext>}}\text{= (1.35 ± 0.11 ± 0.22)}\text{keV}$ and a total width of (47_?15⁺³⁷ keV.     

Spin dependence of the shape of even-even nuclei within the Davydov-Chaban model

Within a model of a nonaxial even-even nucleus soft in β vibrations, the shape parameters of the ¹⁵⁴Gd, ^156,158,160Dy, ^164,168Er, ¹⁶⁸Yb, ¹⁷⁶Hf, and ¹⁸⁰W nuclei are calculated in the quadrupole approximation as functions of the excited-state spin.     

Determination of the radiative widths of the η′ and A2 from two-photon exchange production

From the two-photon exchange processes e⁺e^? → e⁺e^?η' (958) → e⁺e^??⁰γ and e⁺e^? → e⁺e^?A₂ (1310) → e⁺e^?π⁺π^?π⁰ observed using the CELLO detector at PETRA the radiative widths of the η' and A₂ have been determined with the results: Γ_γγ(η') = 5.4 ± 1.0[stat.] ± 0.7[syst.] keV; Γ_γγ(A₂) = 0.59 ± 0.14[stat.] _?0.08^+0.31[syst.] keV.     

Reexamination of the vacuum ultraviolet emission spectrum of CO in the 950–1200 Å region

New spectrograms of CO below 1200 Å reveal that emission bands terminating on the high energy $\text{E}{}_0{}^1\text{Σ}{}^{\mathrm{+}}$ and ¹Π states plus most of the previously reported unidentified emission bands of CO actually originate from molecular nitrogen. Four new emission band systems in CO, tentatively identified as V¹Π-X¹Σ⁺, W¹Π-X¹Σ⁺, Y¹Σ⁺-X¹Σ⁺, and Z¹Σ⁺-X¹Σ⁺, have been observed. The corresponding T_v0′s are 98917, 102804, 99963, and 105724 cm^?1, respectively.     

Laser spectroscopy of LaF: Determination of the separation of the singlet and triplet state manifolds

Tunable dye lasers have been used to excite several known transitions in LaF. Resolved fluorescence spectra obtained after excitation of B¹Π-X¹Σ⁺ and C¹Π-X¹Σ⁺ bands showed transitions to both X¹Σ⁺ and a³Δ states. Analysis of the spectra shows that the state is 1432 cm⁻¹ above X¹Σ⁺, is at 1808 cm⁻¹, and there is an Ω = 2 state (probably ¹Δ) at 5478 cm⁻¹. A new 0⁺-X¹Σ⁺ (v = 0) band has been observed in the vicinity of the B¹Π-X¹Σ⁺ 1-0 band. High resolution excitation spectra of both bands have been obtained, term energies and rotational constants calculated, and the Λ-doubling in B¹Π, v = 1 has been studied. The principal constants (in cm⁻¹) obtained from the analyses wereThe assignments of the low lying states are discussed in terms of their electron configurations and are shown to be in accord with predictions of Ligand Field Theory.     

Model-independent analysis of the neutral-current interaction in the inclusive neutrino reactions

On the basis of some general assumptions on the deep inelastic structure functions, such as scaling and chiral symmetry we determine the values of {(H _V ³)²+(H _A ³)²}+η{(H _V ⁰)²+(H _A ⁰)²} andH _V ³ H _A ³+ηH _V ⁰ H _A ⁰ whereH _V ^3,0 andH _A ^3,0 are the four coupling constants characterizing the hadronic neutral current andη is the ratio of the isoscalar to isovector structure functions. General expressions are given for the kinematical averages 〈v〉 and 〈Q ²〉 for the neutral-current reactions in terms of the coupling constants. This analysis does not depend on the validity of the quark-parton model.     

A test of the validity of the extraction ofK − π− scattering in the reactionK − p →K −π−Δ++ in the framework of the one-pion-exchange model

In a study of the reactionK ^? p →K ^-π^?π⁺ p at 10 and 16 GeV/c the one-pion-exchange model was tested by attempting to extract on this basis the angular distributions for π⁺ p elastic scattering and comparing to real π⁺ p scattering. In thes-channel frame high order moments already appeared at relatively low mass. In general there are large discrepancies in both thes- andt-channel frames which remain after extrapolation to the pion pole and are related toQ ^? production. The structure of the decay angular distribution of theK ^? K ^- π^- system produced in association with Δ⁺⁺ is dominated by proton diffractive dissociation into Δ⁺⁺π^-.     

Change in the size dependences of the surface properties of nanodiamond upon variation in the isotope composition

The isothermal-isomorphic dependences of the specific surface energy (σ), its isochoric temperature derivative (σ′), and surface pressure (P _sf) on the size of nanodiamonds ¹²C and ¹³C at 100 and 4300 K are calculated. It is shown that the ratio σ(¹²C)/σ(¹³C) decreases with decreasing size along both isotherms, and σ′(¹²C)/σ′(¹³C) increases with decreasing size, and this effect is higher at lower temperatures. The ratio P _sf(¹²C)/P _sf(¹³C) increases with decreasing size. The effect is stronger at higher temperatures.     

Status of the theory of the hydrogen Lamb shift

The theory of the 2S _1/2-2P _1/2 Lamb shift of hydrogen is reviewed and compared to experiment. Recent corrections from radiative recoil of order α(Zα)⁵ m ² /M and pure recoil of order (Zα) ⁶ m ² /M are discussed. Contributions of order α ² (Zα) ⁵ m have been calculated from certain classes of diagrams. These are described while other as yet uncalculated terms are mentioned. The largest error in the theory is due to the uncertain measured value of the proton electromagnetic radius.     

On the dissociation of the ozone dication

A mechanism for the dissociation of the ozone dication formed by double ionisation of neutral O₃ is determined by ab initio calculations. The dication ground singlet state is found to have a linear equilibrium geometry that is stable with respect to dissociation to O⁺ and O₂⁺. However, at the Franck-Condon zone for formation of O₃²⁺ from the neutral molecule the singlet potential energy surface intersects with a dissociative triplet state. We propose that crossing to this dissociative triplet state can account for the absence of any long-lived O₃²⁺ ions in the electron-impact mass spectrum of ozone. Further calculations of the kinetic energy release for the fragmentation of O₃²⁺ to O⁺+O₂⁺ indicate that considerable vibrational excitation may be present in the O₂⁺ ion.