Electromagnetic Self-Energy Contribution to M p -M n and the Isovector Nucleon Magnetic Polarizability
Not Available
Walker-Loud, André↗
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Isovector giant E2 resonance and overtone of the isovector giant E1 resonance in photonucleon reactions
The effect of the isovector giant quadrupole resonance and an overtone of the isovector giant dipole resonance on the photodisintegration of medium-mass and heavy nuclei in the energy range of 20-40 MeV is studied on the basis of a combined model of photonucleon reactions. Basic features of these resonances are evaluated within a semimicroscopic approach. Their deformation spitting is described on the basis of the model of polarization vibrations of a two-component nuclear liquid.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Stochastic method with low mode substitution for nucleon isovector matrix elements
Not Available
Yang, Yi-Bo↗
Lattice calculation of nucleon isovector axial charge with improved currents
We employ dimension-4 operators to improve the local vector and axial-vector currents and calculate the nucleon isovector axial coupling $g$ ${^3}_{A}$ with overlap valence on 2 + 1-flavor domain wall fermion (DWF) sea. Using the equality of $g$ ${^3}_{A}$ from the spatial and temporal components of the axial-vector current as a normalization condition, we find that $g$ ${^3}_{A}$ is increased by a few percent towards the experimental value. Here, the excited-state contamination has been taken into account with three time separations between the source and sink. The improved axial charges $g$ ${^3}_{A}$ (24I) = 1.22 (4) (3) and $g$ ${^3}_{A}$ (32I) = 1.21 (3)(3) are obtained on a 24 3 × 64 lattice at pion mass of 330 MeV and a 32 3 × 64 lattice at pion mass 300 MeV and are increased by 3.4% and 1.7% from their unimproved values, respectively. We have also used clover fermions on the same DWF configurations and find the same behavior for the local axial charge as that with overlap fermions.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Deformation dependence of the isovector giant dipole resonance: The neodymium isotopic chain revisited
Not provided.
Astronomy & Astrophysics↗
On the importance of np-pairs in the isovector pairing model
Abstract It is shown that the isovector np-pair number operator can be realized in the O (5) quasi-spin basis. The computation of the isovector np-pair number is demonstrated for even-even and odd-odd ds -shell nuclei described by the charge-independent mean field plus isovector pairing model restricted within the O (5) seniority-zero subspace, thereby binding energies and low-lying excited states of these ds -shell nuclei are fit, along with estimates for the isovector neutron-proton pairing contributions. For reasonable neutron-proton pairing strengths the isovector np-pairing energy contribution to the total binding energy in odd-odd N = Z nuclei is systematically larger than that in the even-even nuclei. In sum, the results suggest that the isovector np-pairing mode is favored in odd-odd N = Z nuclei; and additionally, a decrease in the double binding-energy difference for odd-odd nuclei is primarily due to the symmetry and Wigner energy contributions to the binding energy.
Physics↗
Neutron-proton pairing correction in the extended isovector and isoscalar pairing model
An extended O ST (8) model with multi j-orbits is constructed based on the angular momentum decomposition with “pseudo”-spin S for valence nucleons in a j-orbit. It is shown that the isovector S = 0 and T=1 pairs are exactly the J=0 and T=1 pairs in a given j-orbit, while the isoscalar S = 1 pairs are linear combinations of J=odd pairs, with which the pairing Hamiltonian can be used to estimate isovector and isoscalar pairing interactions. As an example of the model application, some low-lying J = 0 + level energies of even-even and odd-odd A=18 – 28 nuclei up to the half-filling in the ds-shell above the 16 O core are fit by the model and compared with the fitting results of the same Hamiltonian in the O LST (8) form. It has been verified from the fitting of both the models that the isoscalar pairing interaction can be neglected in the lower energy part of the spectra of these ds-shell nuclei as far as binding energies and a few J=0 + excited levels of these nuclei are concerned. With the mean-field plus isovector pairing interaction only, neutron-neutron, proton-proton, and neutron-proton pairing contributions at the ground or the lowest J=0 + state of these nuclei are estimated. It is shown that the isovector np-pairing contribution to the binding in the odd-odd N=Z nuclei is systematically larger than that in the even-even nuclei. Furthermore, the isoscalar np-pair content at the lowest J=0+ state of these nuclei is also estimated. In both the O ST (8) and O LST (8) models, it is clearly shown that the isoscalar-pair content in the lowest J=0 + state of the N=Z and N=Z±2 nuclei increases with increasing of the valence nucleons, especially in those even-even nuclei, which indicates the isoscalar pairing correlation to be of importance at low-lying states of N=Z and N=Z±2 nuclei, especially in those even-even nuclei with more valence nucleons up to the half-filling, even though the isoscalar pairing interaction is negligible.
20 ≤ A ≤ 38↗
Isovector pairing and quartet condensation in N=Z nuclei
We introduce and study a quartet condensate model (QCM) to treat the isovector pairing correlations in N=Z nuclei, by conserving the particle number and the total spin and isospin in the ground state of such nuclei. For the calculations we choose different isovector pairing forces acting on spherical and axially deformed single particle states. The results show that the QCM model describes very well the isovector pairing correlations for nuclear systems with N=Z.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Isovector Q balls
Finite-energy solutions rotating at a constant angular velocity in isovector space are considered within theories that possess global SO(3) symmetry (isovector theories). It is shown that, for a nonlinear O(3) model (n field), such solutions exist only in the one-dimensional case. For the isovector theory proposed by S. Weinberg in order to describe low-energy properties of the {pi} mesons, such solutions exist at some values of parameters that appear in this theory. Some properties of these solutions are studied.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Extraction of the non-spin- and spin-transfer isovector responses via the 12 C ( 10 Be, 10 B + 𝛾) 12 B reaction
The isovector response in 12 B was investigated via the 12 C ( 10 Be, 10 B + 𝛾) 12 B* reaction at 100𝐴MeV. By utilizing the 𝛾-decay properties of the 1.74 MeV 0 + and 0.718 MeV 1 + states in 10 B, the separate extraction of the non-spin-transfer (Δ𝑆 = 0) and spin-transfer (Δ𝑆 = 1) isovector responses up to an excitation energy of 50 MeV in 12 B in a single measurement is demonstrated. The experimental setup employed the S800 spectrometer to detect and analyze the 10 B ejectiles and the Gamma-Ray Energy Tracking In-beam Nuclear Array (GRETINA) for obtaining the Doppler-reconstructed spectrum for 𝛾 rays emitted in flight by 10 B. A 12 C foil was placed at the pivot point of the spectrograph. Here, the 12 B reaction product was not detected. Contributions from transitions associated with the transfer of different units of angular momentum in the non-spin- and spin-transfer responses were analyzed using a multipole decomposition analysis. The extracted non-spin-dipole (Δ𝑆 = 0, Δ𝐿 = 1) and spin-dipole (Δ𝑆 = 1, Δ𝐿 = 1) responses were found to be consistent with available data from other charge-exchange probes, validating the non-spin- and spin-transfer filters used. While statistical uncertainties and experimental resolutions were relatively large due to the modest intensity of the 10 Be secondary beam, the results show that, with the much higher intensities that will be available at new rare-isotope beam facilities, the ( 10 Be, 10 B + 𝛾) reaction and its Δ𝑇 𝑧 = −1 partner, the ( 10 C, 10 B + 𝛾) reaction, are powerful tools for elucidating the isovector non-spin- and spin-transfer responses in nuclei.
Charge-exchange reactions↗
Isoscalar and isovector giant resonances in 92,94,96,98,100 $\mathrm{Mo}$ and 90,92,94 $\mathrm{Zr}$
The response functions, S(E), and centroid energies, E CEN , of the isoscalar and isovector giant resonances of multipolarity L = 0 - 3 in 92,94,96,98,100 Mo and 90,92,94 Zr have been calculated employing the spherical Hartree-Fock (HF) based random phase approximation (RPA) method, using the Skyrme-type effective nucleon-nucleon interaction. In particular, we investigate the recent experimental results of the uncharacteristic behavior of E CEN for the isoscalar giant resonances, by extending our HF-based RPA calculations with only the KDE0v1 interaction to 32 additional Skyrme interactions. The main result of our investigation is that we find significant disagreements between the theoretical and the experimental values of E CEN for isoscalar giant monopole and dipole resonance of some nuclei. For the isoscalar giant octupole resonance we find the theoretical values of the E CEN to be well above the experimental results. We also study the sensitivity of E CEN to nuclear matter (NM) properties, including the effective mass, the incompressibility coefficient and the symmetry energy at saturation density, by determining the Pearson linear correlation coefficient between the calculated values of E CEN and the various nuclear matter properties of each Skyrme parametrization. So, for the isovector giant dipole resonance we find good agreement between the experimental and theoretical values of E CEN for Skyrme interactions with values of the enhancement coefficient of the energy weighted sum rule, κ, in the range between 0.25 – 0.70
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Measurement of the isovector axial form factor at Q{sup 2} = 0.23 (GeV/c){sup 2}
We present the preliminary value of the measurement of the parity violating asymmetry in the cross section of quasi-elastic scattering of longitudinally polarized electrons on deuteron at backward angles at Q{sup 2} = 0.23. The preliminary asymmetry is A{sub PV}{sup d}(Q{sup 2} = 0.23) = (−20.77±0.84{sub stat}±1.23{sub syst})10{sup −6}. From this value a preliminary linear combination of the G{sub M}{sup s} and the isovector axial form factor G{sub A} can be extracted G{sub A}{sup T = 1}+0.59G{sub M}{sup s} = −0.53±0.37±0.02. Combining this preliminary linear combination with that extracted from the measurement of the parity violating asymmetry on proton, already publish, it is possible to disentagle the form factors and thus we can obtain a preliminary experimental determination of the isovector axial form factor G{sub A}{sup T = 1} = −0.43±0.46.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Ratio of isoscalar to isovector core polarization for magnetic moments
In calculations of isoscalar magnetic moments of odd-odd N=Z nuclei, it was found that, for medium- to heavy-mass nuclei, large-scale shell-model calculations yielded results that were very close to those obtained with the much simpler single-j shell model. To understand this, we compare isoscalar and isovector core-polarization configuration-mixing contributions to the magnetic moments of mirror pairs in first-order perturbation theory, using a spin-dependent {delta} interaction. We fit the strength of the {delta} interaction by looking at isovector and isoscalar mirror pairs. We then use the same interaction to calculate corrections due to first-order core polarization of the magnetic moments of odd-odd nuclei.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
The {phi}(1020)a{sub 0}(980) S-wave scattering and hints for a new vector-isovector resonance
We have studied the {phi}(1020)a{sub 0}(980) S-wave scattering at threshold energies employing chiral Lagrangians coupled to vector mesons by minimal coupling. The interaction is described without new free parameters by considering the scalar isovector a{sub 0}(980) resonance as dynamically generated in coupled channels and demanding that the recently measured e{sup +}e{sup -}{yields}{phi}(1020)f{sub 0}(980) cross section is reproduced. For some values of a parameter obtained by fitting the latter reaction cross section, and taking the a{sub 0}(980) pole position and residues from two previous studies, the presence of a dynamically generated isovector companion of the Y(2175) is revealed. We have also investigated the corrections to the e{sup +}e{sup -}{yields}{phi}(1020){pi}{sup 0}{eta} cross section that arise from {phi}(1020)a{sub 0}(980) rescattering in the final state. They are large and lead to considerable modifications of the cross section in absolute value and energy dependence. Moreover, when a {phi}(1020)a{sub 0}(980) resonance is present, it shows up as a clear resonant peak at {radical}(s){approx}2.03 GeV in e{sup +}e{sup -}{yields}{phi}(1020){pi}{sup 0}{eta} from the {phi}(1020)a{sub 0}(980) final-state interactions.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Simplest photonuclear reactions accompanied by the excitation of isovector giant dipole and quadrupole resonances: Semimicroscopic description
A semimicroscopic approach based on the continuum version of the random-phase approximation (CRPA) and on a semiphenomenological inclusion of the fragmentation effect is applied to describing cross sections for photoabsorption and direct plus semidirect and inverse reactions accompanied by the excitation of isovector giant dipole and quadrupole resonances. In addition to the spinless part of the Landau-Migdal interaction and a partly self-consistent phenomenological mean field of the nucleus, that version of the approach which is used here takes into account isovector separable velocity-dependent forces, as well as the effect of the fragmentation shift of the giant-resonance energy. The results obtained by calculating various features of the aforementioned cross sections for a number of magic and semimagic medium-mass nuclei are compared with respective experimental data.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Separation of contributions of isovector E2 and E1 giant resonances in direct and inverse reactions with real and virtual photons
A brief overview of the methods for separating the contributions of isovector electric quadrupole (E2) and dominant dipole (E1) giant resonances in atomic nuclei, which are excited in direct and inverse reactions with photons (real and virtual), is given. The basic parameters of isovector giant resonance E2, which were declared to date by applying some of these methods to the results with {sup 208}Pb, are also presented.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗