Superallowed Fermi Beta Research Articles

Exotic phenomena in medium mass N ≃ Z nuclei within the beyond-mean-field approach

Recent studies on properties of proton-rich nuclei in the A = 70 mass region brought insights into fundamental symmetries and interactions and produced characteristics required by the astrophysical scenarios on the rp-process path revealing coexistence phenomena which dominate the structure and dynamics of these exotic nuclei. Isospin mixing and related phenomena like Coulomb energy differences, mirror energy differences, triplet energy differences as well as superallowed Fermi beta decay in isovector triplets have been investigated. The interplay between isospin-symmetry-breaking and shape-coexistence effects on isospin-related phenomena in nuclei as well as weak interaction processes under terrestrial and stellar x-ray burst environment have been explored in the frame of the beyond-mean-field complex Excited Vampir variational model. We used an adequate model space and the effective interaction was derived from a G-matrix starting from the charge-dependent Bonn CD potential. Results concerning the influence of shape coexistence and mixing on the structure and β-decay properties of exotic nuclei will be reviewed.

The influence of pairing correlations on the isospin symmetry breaking corrections of superallowed Fermi beta decays

Within the framework of quasi-particle random phase approximation, the isospin breaking correction of superallowed 0+ → 0+ beta decay and unitarity of Cabibbo-Kobayashi-Maskawa mixing matrix have been investigated. The broken isotopic symmetry of nuclear part of Hamiltonian has been restored by Pyatov’s method. The isospin symmetry breaking correction with pairing correlations has been compared with the previous results without pairing. The effect of pairing interactions has been examined for nine superallowed Fermi beta decays; their parent nuclei are 26Al, 34Cl, 38K, 42Sc, 46V, 50Mn, 54Co, 62Ga, 74Rb.

The ft values of the superallowed Fermi beta decays

In this work, the ft values of the 0+→0+ superallowed Fermi beta decays have been investigated. In the calculations, the shell model has been modified by Pyatov’s restoration method because of the isospin breaking and the transition matrix elements have been found by means of the quasi-particle random phase approximation (QRPA).

The Influence of Pairing Correlations on the Isospin Symmetry Breaking Corrections of Superallowed Fermi Beta Decays

The Influence of Pairing Correlations on the Isospin Symmetry Breaking Corrections of Superallowed Fermi Beta Decays

The isospin mixing and the superallowed Fermi beta decay

In the present work, the isospin admixtures in the nuclear ground states of the parent nuclei and isospin structure of the isobar analog resonance (IAR) states have been investigated by studying the 0 + →0 + superallowed Fermi β decays using Pyatov’s restoration method. Within the random phase approximation (RPA), in this method, the effect of isospin breaking due to the Coulomb forces has been evaluated, taking into account the effect of pairing correlations between nucleons.

Superallowed Fermi Beta Decay and the Unitarity of the Cabibbo-Kobayashi-Maskawa Matrix

In this work, the unitarity of the Cabibbo-Kobayashi-Maskawa (CKM) mixing matrix has been investigated by studying the eleven well-known superallowed Fermi Beta decays; their parent nuclei are 10C, 14O, 26Al, 34Cl, 38K, 42Sc, 46V, 50Mn, 54Co, 62Ga, and 74Rb. The numerical value of the Vud element of the CKM mixing matrix has been calculated following the standart procedure. Using a different method from those of the previous studies, the effect of the isospin breaking due to the Coulomb forces has been evaluated more accurately. Here, the shell model has been modified by Pyatov’s restoration because of the isospin breaking and the transition matrix elements have been found by means of the random phase approximation (RPA)

Precise half-life measurement for the superallowed 0(+)-->0(+) beta emitter (74)Rb: first results from the new radioactive beam facility (ISAC) at TRIUMF.

Presently, the world data for superallowed beta decay leads to a result in disagreement (at the 98% confidence level) with the predictions of the minimal standard model for the unitarity of the Cabibbo-Kobayashi-Maskawa matrix. Precise data for the superallowed 0(+)-->0(+) beta decay of (74)Rb would provide a critical test of the nucleus-dependent isospin symmetry-breaking corrections that must be calculated for these superallowed Fermi beta decays. The present work reports the first precise measurement of the half-life for (74)Rb ( t(1/2) = 64.761+/-0.031 ms). The data were obtained at the radioactive beam facility (ISAC) at TRIUMF using a beam of approximately 4000 (74)Rb ions s(-1).

Radiative corrections to 10C superallowed Fermi beta decay.

In view of new data on the {sup 10}C superallowed Fermi {beta} decay, the radiative corrections have been reevaluated. In particular we calculate and include the nuclear-structure-dependent part of the axial-vector-induced contribution to the {ital O}({alpha}) radiative correction. The resulting {ital V}{sub {ital u}{ital d}} is appreciably larger than a value recently published, which was based on the same data.

Branching ratio for 10C superallowed Fermi beta decay.

The branching ratio for $^{10}\mathrm{C}$ superallowed Fermi \ensuremath{\beta} decay has been measured accurately by a newly developed method. The result is 1.473\ifmmode\pm\else\textpm\fi{}0.007 %. The Ft value is derived as 3065.4\ifmmode\pm\else\textpm\fi{}14.7 sec, which is consistent with the Ft values determined accurately for heavier nuclei and with predictions of conserved vector current hypothesis. The method developed here can be applied to the high precision \ensuremath{\beta}-\ensuremath{\gamma} spectroscopy.

The Kobayashi-Maskawa matrix element mod Vud mod from neutron β-decay

Using only data from the beta -decay of the neutron, the Kobayashi-Maskawa matrix element mod Vud mod is calculated to be 0.979+or-0.003. Measurements of the beta -decay asymmetry, providing the ratio of the axial coupling constant to the vector coupling constant GA/GV, are combined with measurements of the neutron lifetime to determine the vector coupling constant, from which mod Vud mod is calculated. The values of GV and mod Vud mod are in agreement with those determined from superallowed Fermi beta -decays in nuclei.

Gv, KM and mt

Analysis of superallowed Fermi beta decay using a new approach to the nuclear mismatch factor and evaluation of the radiative corrections using renormalization group methods and including nuclear-structure-dependent terms in the “inner” radiative correction leads to | V ud| 2+| V us| 2+| V ub| 2 = 0.9999 ± 0.0012 for the first row of the Kobayashi-Maskawa matrix using a mass of 130 GeV for the top quark. We may, alternatively, assuming unitarity of the KM matrix, infer a top quark mass of (1.40±80) GeV from beta-decay data alone.

The vector coupling constant and the Kobayashi-Maskawa matrix

Abstract Data on superallowed Fermi beta decay are analyzed using recent developments in our understanding of radiative corrections and using a novel largely-empirical approach to the nuclear mismatch correction. The resultant value for the operational vector coupling constant G1v is: G′ v /( h 3 = (1.1510±0.0005) × 10 −5 GeV −2 . The test for the unitarity of the first row of the Kobayashi-Maskawa matrix gives: |Vud|2 + |Vus|2 + |Vud|2 = 0.9989±0.0012.