Charge-symmetry breaking and n-n scattering lengths

Recent experimental and theoretical investigations of ρ-ω and η-π mixing have caused us to re-examine the effects of these mixings on the charge-symmetry breaking of nuclear forces. The charge asymmetry of the nucleon-nucleon force in the singlet S-state is used to predict the n-n scattering length in terms of the measured p-p one. The extra attraction of the n-n potential in the ¹S₀ state gives rise to a change of roughly −0.8 fm in the corresponding scattering length. The magnitude (and sign) of the charge asymmetry is approximately that required to understand the binding-energy differences of the mirror nuclei ³He-³H and ⁴¹Sc-⁴¹Ca.     

Determination of low-energy parameters of neutron-neutron scattering from an analysis of the binding-energy difference between the 3H and 3He mirror nuclei

A relation between quantities that characterize the breaking of the charge symmetry of nuclear forces in systems of two and three nucleons is found on the basis of an analysis of the binding-energy difference between the ³H and ³He mirror nuclei. For the neutron-neutron scattering length and effective range, the values of a _nn = ?18.38(55) fm and r _nn = 2.84(4) fm, respectively, were obtained by using purely nuclear parameters of proton-proton scattering in the ¹ S ₀ state. The calculated values agree with present-day experimental results.     

Δ-isobar contributions to the charge asymmetry of the three-nucleon bound states

Mechanisms of isospin violation in the nuclear force due to the Δ-isobar are studied. They arise from the coupling of the Δ to the photon and from the charge splitting of the Δ-mass. The charge-asymmetry contribution of the Δ to the ³He-³H binding-energy difference is calculated. Cancellations between different mechanisms are found yielding a small total result. The effect of the photon-induced Δ-excitation, traditionally considered, is negligible. The uncertainty in the Δ-mass splitting shows up in a sizeable theoretical uncertainty for the total result.     

Electronuclear sum rules. Improved realization and statement. Experiment and theory for4He

The experimental (e, e′) data in the region of highω, necessary for a reliable check of sum rules, are either unavailable or dominated by pion degrees of freedom. To calculate the corresponding sums over (e, e′) spectra, a reliable extrapolation of spectra to this region is proposed. It is based on a quasi-y-scaling type behavior of the spectra. It is shown that the sum rule version corresponding to the summation of the spectra at constantE ₀ andθ, being simplest from the experimental viewpoint, can be made accurate enough if an experimental spectrum is used to estimate the parameters involved in it. It is found that for⁴He nucleus, one of the existing groups of the experimental spectra is in a good agreement with the model-independent sum rule which corresponds to the single-particle approximation for the interaction of a nucleus with an electromagnetic field, while the second group of spectra leads to a considerable deviation from the sum rule.     

Charge and mass radii of the tin isotopes

Data on the isotope shift of the nuclear charge densities of the tin isotopes and of their mean square charge radii are considered from the viewpoint of the Hartree-Fock and Droplet Models. Attention is paid to the electromagnetic corrections of order 1/m². Through a leptodermous analysis of charge and matter densities we find: (i) differences of m.s. charge radii are mainly sensitive to the external region, (ii) the electromagnetic corrections are important in that region, (iii) despite different leptodermous properties, forces Ska and GO-P lead to the same neutron skin thickness. The average rate of variation of the proton m.s. radius is interpreted as favouring either a low valueQ≈30 MeV for the droplet model asymmetry parameter, or a zero value for the saturation asymmetry parameterL.     

CP-Violating charge asymmetry in the decay KL → πμν

The K_μ3⁰ charge asymmetry has been measured to be (6.0 ± 1.4) × 10⁻³. The error contains a major systematic contribution. Large corrections were made in order to exclude neutron-induced background events and to correct for the range difference between μ⁺ and μ⁻.     

Theoretical study on the 1s22s-1s2 np transitions for Ni25+ ion

The transition energies, wavelengths and oscillator strengths for the 1s²2s-1s² np (n ? 9) transitions of Ni²⁵⁺ ion are calculated. In calculation of the energies, we not only take account of the firstorder corrections from relativistic and mass-polarization effects, but also estimate the higher-order relativistic contribution and QED correction by introducing the effective nuclear charge. The results agree with experimental data available in literature satisfactorily. Grotrian diagram showing these transitions is given.     

Formation of highly excited states of 6He in the 9Be(π−, tt)t reaction

The hypothesis of a heavy stable quark of the fourth family can provide a nontrivial solution for cosmological dark matter if baryon asymmetry in the fourth family has a negative sign and an excess of ū antiquarks with charge (?2/3) is generated in the early Universe. Excessive ū antiquarks form (ūūū) antibaryons with electric charge ?2, which are all captured by ⁴He and trapped in a [⁴He⁺⁺(ūūū)^??] O-helium OHe “atom” as soon as ⁴He is formed in Big Bang nucleosynthesis. Interaction of O-helium with nuclei opens a new path to the creation of heavy nuclides in Big Bang nucleosynthesis. Due to the large mass of the U quark, OHe “atomic” gas decouples from baryonic matter and plays the role of dark matter in large-scale structure formation with structures on small scales being suppressed. Owing to nuclear interaction with matter, cosmic O-helium from the galactic dark matter halo is slowed in the Earth below the thresholds of underground dark matter detectors. However, an experimental test of this hypothesis is possible in the search for OHe in balloon-borne experiments and for U hadrons in cosmic rays and accelerators. OHe “atoms” might form anomalous isotopes and could cause cold nuclear transformations in matter, offering a possible way to exclude (or prove) their existence.     

Study of emission characteristics of the projectile fragments produced in the interaction of 84Kr36 with nuclear emulsion detector at 1 GeV

This article is focused on the characteristics of the projectile fragments of charge 1 ≤ Z ≤ 10 produced in the interaction of the ⁸⁴Kr₃₆ with nuclear emulsion detector at 1 GeV per nucleon. We have studied the average charge distribution and multiplicity distribution of the projectile fragments having charge 1 ≤ Z ≤ 10. We have also studied the emission behavior of various projectile fragments produced from the interaction with different target groups of nuclear emulsion detector. From this study we have observed that the emission of projectile fragments is strongly dependent on the interaction with different type of the target groups of nuclear emulsion detector as well as on the mass of the projectile beam. The results are compared with other experimental observations carried out at relativistic energy and found to be consistent.     

Momentum and density dependence of the ph interaction in continuum RPA calculations with Skyrme forces

We analyse the momentum and density dependence of the ph interaction in self-consistent RPA calculations of electromagnetic reactions with Skyrme forces. First, we calculate the V⁰⁰_ph and V⁰¹_ph spin-isospin components in nuclear matter for an SK3 interaction. At the nuclear surface, they have decreasing values with increasing q-values up to momenta q=3 fm⁻¹. As a second point, we show that the predictions of the ¹²C(e, e') charge response at 400 MeV/c remain practically unchanged when the zero-range quadratic momentum dependence of the SK3 interaction is replaced by the momentum dependence associated with a Yukawa short-ranged force.     

A possible estimate of the elementary length in electromagnetic interactions

The difference of 0·2 MHz between the theoretical and experimental values of the Lamb shift of the hydrogen terms 2s _1/2 and 2p _1/2 is used to estimate the elementary length λ in an electromagnetic interaction. The calculated difference of the hydrogen terms in the Bopp-Podolsky potential field\(\varphi (r) = \frac{e}{{4\pi r}}(1 - e - ^{r/\lambda } )\) is compared with the given difference Δ?0·2 MHz. From this we then get for the elementary length λ?0·1× 10^-13 cm. The distribution of the electric charge in the proton\(\varrho (r) = \frac{e}{{4\pi \lambda ^2 }}\frac{{e - ^{r/\lambda } }}{{^ - r}}\) leads to the Bopp-Podolsky potential if the Coulomb interaction is assumed to be valid in the whole space.     

Nuclear longitudinal form factors for axially deformed charge distributions expanded by nonorthogonal basis functions

In this paper,the nuclear longitudinal form factors are systematically studied from the intrinsic charge multipoles.For axially deformed nuclei,two different types of density profiles are used to describe their charge distributions.For the same charge distributions expanded with different basis functions,the corresponding longitudinal form factors are derived and compared with each other.Results show the multipoles C_λ of longitudinal form factors are independent of the basis functions of charge distributions.Further numerical calculations of longitudinal form factors of~(12)C indicates that the C_0 multipole reflects the contributions of spherical components of all nonorthogonal basis functions.For deformed nuclei,their charge RMS radii can also be determined accurately by the C_0 measurement.The studies in this paper examine the model-independent properties of electron scattering,which are useful for interpreting electron scattering experiments on exotic deformed nuclei.     

Mass Distributions and Charge Dispersion for the Nuclear Fission

The theory of nuclear fission is reconsidered by introducing the charge asymmetry in the asymmetric two center shell model as a dynamical collective coordinate. The quantum mechanical fluctuations, which are accompanied with the collective motion as a function of the mass asymmetry, are responsible for the mass distributions in nuclear fission. Numerical calculations are carried out for the mass distributions and charge dispersions for the nuclear fission of the ²³⁶U and ²³⁸U nuclei. The present obtained theoretical calculations are in good agreement with the experimental measurements.     

Three-nucleon interaction in 3-, 4- and ∞-body systems

We report results of variational calculations of ³H, ³He, ⁴He and nuclear matter with the Urbana v₁₄ two-nucleon interaction and realistic models of the three-nucleon interaction (TNI). These include the Tucson and isobar intermediate-state models of the two-pion exchange TNI. The latter is also studied with an intermediate-range three-nucleon repulsion. In general, realistic TNI helps to bring the theory closer to experiment by giving extra binding energy to the A = 3 and 4 nuclei and providing extra saturation to the nuclear matter binding energy. The Coulomb energy of ³He and the rms radii of A = 3, 4 nuclei are also well described. However, some problems remain unresolved. There is a slight overbinding of ⁴He, an underbinding of nuclear matter, and the charge form factors of ³He and ⁴He, calculated with impulse approximation, deviate from the experimental at q²>5 fm^?2.     

Isotope shifts in transitions between low-lying levels of Sr I by laser-atomic-beam spectroscopy

High-resolution laser-atomic-beam spectroscopy has been used to determine isotope shifts in five transitions between low-lying states of Sr I. With these results and existing data a parametric analysis of level isotope shifts has been performed. The transition isotope shifts have been separated into field shift and mass shift contributions with a King-plot procedure using model-independent nuclear charge equivalent radiiR _k from muonic x-ray measurements. Values for the mean-square nuclear charge radiiδ〈r ₂ 〉 have been calculated from the field shifts in the optical transitions 5s ^{2 1} S ₀-5s5p ³ P ₁ and 5s5p ³ P ₀-5s6s ³ S ₁ and compared with correspondingδ〈r ² 〉 values evaluated from muonic x-ray data.     

Discrete ambiguity in the experimental 40Ca charge density

Elastic electron scattering and muonic X-ray data are used to determine the ⁴⁰Ca charge density in a model-independent manner. A discrete ambiguity of ρ(r) at small radii is discovered. An analysis of ³⁹K and ⁴⁸Ca data does not allow to remove this ambiguity.     

The decay of theT=1 isospin triplet inA=12 systems. III. Higher order effects in the evaluation of the asymmetry parameters α∓ for the electron emission from aligned12B and12N

Nuclear Structure: calculation of the asymmetry α_? ofβ rays emitted from polarized¹²B and¹²N nuclei including higher order contributions. Comparison with recent experimental values. The asymmetry parameters α_? and α₊ were evaluated including higher order corrections in the framework of the formulae derived in a previous paper. It was found that since α_? is affected by strong cancellation effects the corrective terms give in this case a very important contribution. The agreement between predicted theoretical values and very recent experimental data is excellent for bothβ ^? andβ ⁺ decays. The experimental results can be understood without invoking the existence of the induced pseudotensor interaction.     

On the behaviour of Er3+ ion in tetragonal crystalline field

Crystal field parameters for ErGaG and Er³⁺ YAlG and used to compute the temperature dependence of Schottky specific heat, paramagnetic susceptibility, magnetic anisotropy,μ _eff and quadrupole splitting in the range 10–400 K. The hyperfine interaction parametersA andB for¹⁶⁶Er and¹⁶⁷Er in both the systems are also obtained and in turn used to estimate the nuclear specific heat contribution. The studied parameters compare well with the available experimental results.     

Determination of the πN charge exchange scattering amplitude from the experimental data at high energies

The difference between theπ ⁺ p andπ ^? p diffraction peaks is used for an estimate of the imaginary part of the charge exchange scattering amplitude. The imaginary part has a narrow peak in the forward direction and passes over to negative values at a momentum transfert of about ?0.15(GeV/c)². If the charge exchange amplitude is dominated by the contribution of theρ Regge pole, the peak is mainly due to thet-dependence of the residue function and a narrow forward peak is expected in the charge exchange angular distribution.