We calculate the nuclear matrix element for the two-neutrino ββ decay of 136Xe into the first excited 0+ state of 136Ba. We use different many-body methods: the quasiparticle random-phase ...approximation (QRPA) framework, the nuclear shell model, the interacting boson model (IBM-2), and an effective field theory (EFT) for β and ββ decays. While the QRPA suggests a decay rate at the edge of current experimental limits, the shell model points to a half-life about two orders of magnitude longer. The predictions of the IBM-2 and the EFT lie in between, and the latter provides systematic uncertainties at leading order. An analysis of the running sum of the nuclear matrix element indicates that subtle cancellations between the contributions of intermediate states can explain the different theoretical predictions. For the EFT, we also present results for two-neutrino ββ decays to the first excited 0+ state in other nuclei.
Ordinary muon capture (OMC) on 100Mo is studied both experimentally and theoretically in order to access the weak responses in wide energy and momentum regions. The OMC populates states in 100Nb up ...to some 50 MeV in excitation energy. For the first time the associated OMC strength function has been computed and compared with the obtained data. The present computations are performed using the Morita-Fujii formalism of OMC by extending the original formalism beyond the leading order. The participant nuclear wave functions are obtained in extended no-core single-particle model space using the spherical version of proton-neutron quasiparticle random-phase approximation (pnQRPA) with two-nucleon interactions based on the Bonn one-boson-exchange G matrix. Partial restoration of the isospin symmetry is implemented in the calculations by separately fitting the isoscalar and isovector parts of the particle-particle interaction strength of pnQRPA. Both the computed and experimental OMC strength distributions show a giant resonance at around 12 MeV. Further measurements and calculations of the OMC strength functions for double-beta-decay daughter nuclei could enable access to in-medium renormalization of the weak axial couplings and pave the way to improved accuracy of the double-beta-decay nuclear matrix elements.
The
98
Mo double-beta decay
Q
-value has been measured, and the corresponding nuclear matrix elements of neutrinoless double-beta (
0
ν
β
β
) decay and the standard two-neutrino double-beta (
2
ν
β
β
...) decay have been provided by nuclear theory. The double-beta decay
Q
-value has been determined as
Q
β
β
=
113.668
(
68
)
keV using the JYFLTRAP Penning trap mass spectrometer. It is in agreement with the literature value,
Q
β
β
=
109
(
6
)
keV, but almost 90 times more precise. Based on the measured
Q
-value, precise phase-space factors for
2
ν
β
β
decay and
0
ν
β
β
decay, needed in the half-life predictions, have been calculated. Furthermore, the involved nuclear matrix elements have been computed in the proton–neutron quasiparticle random-phase approximation (pnQRPA) and the microscopic interacting boson model (IBM-2) frameworks. Finally, predictions for the
2
ν
β
β
decay are given, suggesting a much longer half-life than for the currently observed cases.
In this work we study ordinary muon capture (OMC) on 24Mg from a first-principles perspective. Starting from a particular two- and three-nucleon interaction derived from chiral effective field ...theory, we use the valence-space in-medium similarity renormalization group (VS-IMSRG) framework to construct effective Hamiltonians and muon-capture operators, which nonperturbatively account for many-body physics outside the valence space. Here, the obtained nuclear matrix elements are compared against those from the phenomenological shell model. The impact of including the correlations from the nuclear shell model (NSM) as well as including the induced twobody part is studied in detail. Furthermore, the effects of realistic bound-muon wave function on the operators is studied. Finally, predictions for capture rates to the lowest excited states in 24Na are given and compared with available data. It is found that the spectroscopic properties of 24Mg and its OMC daughter 24Na are fairly well described by both the NSM and VS-IMSRG, and that the effect of the hadronic two-body currents significantly reduces the OMC rates. Both models have some difficulties in matching the measured OMC rates, especially for the 2+ final states. This calls for further studies in other light nuclei with available OMC data.
Abstract
The
$$^{98}$$
98
Mo double-beta decay
Q
-value has been measured, and the corresponding nuclear matrix elements of neutrinoless double-beta (
$$0\nu \beta \beta $$
0
ν
β
β
) decay and the ...standard two-neutrino double-beta (
$$2\nu \beta \beta $$
2
ν
β
β
) decay have been provided by nuclear theory. The double-beta decay
Q
-value has been determined as
$$Q_{\beta \beta }=113.668(68)$$
Q
β
β
=
113.668
(
68
)
keV using the JYFLTRAP Penning trap mass spectrometer. It is in agreement with the literature value,
$$Q_{\beta \beta }=109(6)$$
Q
β
β
=
109
(
6
)
keV, but almost 90 times more precise. Based on the measured
Q
-value, precise phase-space factors for
$$2\nu \beta \beta $$
2
ν
β
β
decay and
$$0\nu \beta \beta $$
0
ν
β
β
decay, needed in the half-life predictions, have been calculated. Furthermore, the involved nuclear matrix elements have been computed in the proton–neutron quasiparticle random-phase approximation (pnQRPA) and the microscopic interacting boson model (IBM-2) frameworks. Finally, predictions for the
$$2\nu \beta \beta $$
2
ν
β
β
decay are given, suggesting a much longer half-life than for the currently observed cases.
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