Isospin mixing of the 1+ states in 12C (original) (raw)
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Isospin mixing of the 1+ doublet in 12C determined by low-energy pion scattering
Physics Letters B, 1990
PSI the inelastic scattering of 50 MeV positive and negative pions to the 1 + excitations at 12.71 MeV (T=0) and 15.11 MeV (T=I) in ~2C has been measured in the angular range 35°-105 °. The angular distributions are in good agreement with impulse approximation calculations. From the double ratio of the 1 + cross sections for n + and n-scattering an isospin mixing matrix element of Ho~-= 157 _+ 35 keV is derived. In contrast to a previous study of this reaction these results do not question the validity of the impulse approximation at low energies.
Isospin Mixing in Nuclei within the Nuclear Density Functional Theory
Physical Review Letters, 2009
We present the self-consistent, non-perturbative analysis of isospin mixing using the nuclear density functional approach and the rediagonalization of the Coulomb interaction in the good-isospin basis. The largest isospin-breaking effects are predicted for N =Z nuclei and they quickly fall with the neutron excess. The unphysical isospin violation on the mean-field level, caused by the neutron excess, is eliminated by the proposed method. We find a significant dependence of the magnitude of isospin breaking on the parametrization of the nuclear interaction term. A rough correlation has been found between the isospin mixing parameter and the difference of proton and neutron rms radii. The theoretical framework described in this study is well suited to describe a variety of phenomena associated with isospin violation in nuclei, in particular the isospin symmetry-breaking corrections to superallowed Fermi beta decays.
Isospin mixing in the nucleon and 4He and the nucleon strange electric form factor
Physical review letters, 2007
In order to isolate the contribution of the nucleon strange electric form factor to the parity-violating asymmetry measured in 4He(e-->],e')4He experiments, it is crucial to have a reliable estimate of the magnitude of isospin-symmetry-breaking (ISB) corrections in both the nucleon and 4He. We examine this issue in the present Letter. Isospin admixtures in the nucleon are determined in chiral perturbation theory, while those in 4He are derived from nuclear interactions, including explicit ISB terms. A careful analysis of the model dependence in the resulting predictions for the nucleon and nuclear ISB contributions to the asymmetry is carried out. We conclude that, at the low momentum transfers of interest in recent measurements reported by the HAPPEX Collaboration at Jefferson Lab, these contributions are of comparable magnitude to those associated with strangeness components in the nucleon electric form factor.
Nuclear Physics A, 2005
Small-angle two-particle correlation functions, involving neutrons and protons, have been measured for E/A = 61 MeV Ar + 112,124 Sn collisions, i.e. systems similar in size but with different isospin asymmetry. The correlation strength of neutron-proton (np) and proton-proton (pp) pairs is stronger for the more neutron-rich system, indicating a shorter average emission time for this system. Comparisons with isospin-dependent BUU transport model simulations are presented, and their implications for the density dependence of the nuclear symmetry energy are discussed.
Isospin Mixing Within the Symmetry Restored Density Functional Theory and Beyond
Acta Physica Polonica B, 2014
We present results of systematic calculations of the isospin-symmetrybreaking corrections to the superallowed I=0 + , T =1 → I=0 + , T =1 βdecays, based on the self-consistent isospin-and angular-momentum-projected nuclear density functional theory (DFT). We discuss theoretical uncertainties of the formalism related to the basis truncation, parametrization of the underlying energy density functional, and ambiguities related to determination of Slater determinants in odd-odd nuclei. A generalization of the double-projected DFT model towards a no core shell-model-like configuration-mixing approach is formulated and implemented. We also discuss new opportunities in charge-symmetry-and charge-independencebreaking studies offered by the newly developed DFT formalism involving proton-neutron mixing in the particle-hole channel.
Isospin mixing and Fermi transitions for some deformed nuclei
We have tried to give a self-consistent explanation of isospin mixing and Fermi beta decays for 54 ≤ Z ≤ 68 deformed nuclei. The effect of isospin impurity in nuclear ground states on Fermi beta transitions has been investigated considering the restoration of symmetry violations stemming from the mean field approximation. The isobar analogue excitations in neighbor odd-odd nuclei have been obtained by following the proton-neutron quasiparticle random phase approximation (pnQRPA) procedure. The dependence of isospin admixture probability on the deformation parameter has been determined for various isotopes of Z = 54-68 nuclei. Then the variations of isobar analogue state energies and the β decay log(ft) values with deformation parameter have been calculated for the same nuclei. Thus, the influences of the isospin symmetry violations on Fermi transitions can be clearly understood.
International Journal of Modern Physics E-nuclear Physics, 2008
Heavy Ion Collisions (HIC) represent a unique tool to probe the in-medium nuclear interaction in regions away from saturation. In this work we present a selection of reaction observables in dissipative collisions particularly sensitive to the isovector part of the interaction, i.e.to the symmetry term of the nuclear Equation of State (EoS). At low energies the behavior of the symmetry
Isospin Symmetry in the Structure Study of Unstable Nuclei
Progress of Theoretical Physics Supplement, 2002
Assuming isospin T is a good quantum number, the analog states of the low-lying states in T z = ±(T 0 +1) nuclei can be found as excited T 0 +1 states in T z = ±T 0 nuclei. Therefore, if T 0 + 1 states are identified in the excited region of T z = ±T 0 nuclei, the structure of unstable nuclei with T z = ±(T 0 + 1) can be deduced. We measured and compared the transition strengths to pairs of excited analog states in inelastic and charge-exchange reactions on the same target nucleus. The T values of these analog states were identified by using the fact that the transition strengths to them are different depending on T. The identification of T = 1/2 and 3/2 nature of analog M 1 and GT states in the mirror nuclei pair 27 Al and 27 Si is reported by comparing the transition strengths in high-resolution 27 Al(p, p) and 27 Al(3 He, t) 27 Si reactions at 0 •. The identified T = 3/2 states are analogous to the low-lying states of 27 Mg, which plays an important role in rp-process of nucleosynthesis.
New information on 12C states from the decays of 12N and 12B
Nuclear Physics A, 2003
The properties of states in "C above the 3a-threshold are of high current interest for nuclear astrophysics and for the nuclear many-body problem in general. We have initiated a series of experiments aimed at elucidating this region by using the P-decays of 12N and "B. By applying the ISOL method for producing these radioactive isotopes, in combination with modern segmented charged particle detectors, our approach has significant advantages over previous studies of this region.
Isospin mixing in nuclei around N=Z and the superallowed beta-decay
Acta Physica Polonica Series B
Theoretical approaches that use one-body densities as dynamical variables, such as Hartree-Fock or the density functional theory (DFT), break isospin symmetry both explicitly, by virtue of charge-dependent interactions, and spontaneously. To restore the spontaneously broken isospin symmetry, we implemented the isospin-projection scheme on top of the Skyrme-DFT approach. This development allows for consistent treatment of isospin mixing in both ground and exited nuclear states. In this study, we apply this method to evaluate the isospin impurities in ground states of even-even and odd-odd N~Z nuclei. By including simultaneous isospin and angular-momentum projection, we compute the isospin-breaking corrections to the 0+ --> 0+ superallowed beta-decay.