arXiv subjects

M. Homma

Publications and source records attributed to M. Homma.

5 recordsLinked to original sources

arXiv2026

Microscopic formulation of the interacting boson-fermion model using the nuclear energy density functional

Microscopic modeling of low-energy spectroscopy in medium-heavy and heavy odd-$A$ nuclei is an outstanding open problem in nuclear physics. We propose a novel spectra-generating collective model for odd-$A$ nuclei constructed by means of the nuclear energy density functional theory and the interacting boson-fermion model. The bosonic Hamiltonian for an even-even nucleus, which is treated as a core, and the strength parameters for the interactions between the core and an odd nucleon are completely determined by using as microscopic inputs the potential energy curves and deformed single-particle spectra obtained from the self-consistent mean-field calculations. In applications to odd-$A$ Eu, Sm, La, and Ba isotopes, we demonstrate the validity of the proposed method in reproducing reasonably the observed low-energy spectra and shape phase transitions in the general cases of the quadrupole collective states, that is, nearly spherical, strongly deformed, and $\gamma$-soft shapes, in the presence of an odd nucleon in a single-$j$ orbit.

nucl-th↗

arXiv2025

Microscopic determination of the interacting boson-fermion model Hamiltonian from the nuclear energy density functional

A microscopic formulation of the interacting boson-fermion model for odd-$A$ nuclei is made using the nuclear energy density functional framework. Strength parameters for the bosonic Hamiltonian and boson-fermion interactions are shown to be determined completely so that energy surfaces and deformed single-particle energies of the Bose-Fermi systems should match the corresponding self-consistent mean-field solutions for fermionic systems. In an illustrative application to axially symmetric odd-$A$ Eu, this procedure is shown to be valid in describing spherical-to-deformed shape phase transitions in odd-$A$ and even-even systems.

nucl-th↗

arXiv2025

Experimental Study of Rare Kaon Decays at J-PARC with KOTO and KOTO II

The rare kaon decay $K_L\to\pi^0\nu\bar{\nu}$ is extremely sensitive to new physics, because the contribution to this decay in the Standard Model (SM) is highly suppressed and known very accurately; the branching ratio is $3\times 10^{-11}$ in the SM with a theoretical uncertainty of just 2%. The measurement of this branching ratio could provide essential new information about the flavor structure of the quark sector from the $s\to d$ transition. The decay is being searched for in the KOTO experiment at J-PARC, which has obtained the current best upper limit on the branching ratio of $2.2\times 10^{-9}$; a sensitivity to branching ratios below $10^{-10}$ is achievable by the end of the decade. A next-generation experiment at J-PARC, KOTO II, was proposed in 2024 with 82 members worldwide, including significant contributions from European members. The goal of KOTO II is to measure the $K_L\to\pi^0\nu\bar{\nu}$ branching ratio with sensitivity below $10^{-12}$ in the 2030s. Discovery of the decay with $5\sigma$ significance is achievable at the SM value of the branching ratio. An indication of new physics with a significance of 90% is possible if the observed branching ratio differs by 40% from the SM value. Another important goal of KOTO II is to measure the branching ratio of the unobserved $K_L\to \pi^0e^+e^-$ decay, which can give an input to flavor structures of new physics. Other rare $K_L$ decays and hidden-sector particles are also in the scope of the study. After 2026, KOTO will be the only dedicated rare kaon decay experiment in the world, and KOTO II is the only future rare kaon decay project currently proposed. We would like to lead a global initiative for the experimental study of rare kaon decays, with significant contributions and support from the European community.

hep-ex↗

arXiv2024

Sensitivity analysis of $\beta$-decay half-life predictions for Ge, As, Zr and Mo nuclei within the mapped interacting boson model

We analyze parameter sensitivities of the mapped interacting boson model (IBM) and boson-fermion-fermion model (IBFFM) in the description of $\beta$-decay properties of the even-mass neutron-deficient Ge and As, and neutron-rich Zr and Mo isotopes. Based on the self-consistent mean-field calculations with a given energy density functional and a pairing interaction, the IBM Hamiltonian for even-even nuclei, single-particle energies, and occupation probabilities for unpaired nucleons, which are necessary building blocks of the IBFFM Hamiltonian and Gamow-Teller and Fermi transition operators, are completely determined. A few coupling constants of the boson-fermion and residual neutron-proton interactions are only phenomenological parameters fitted to reproduce low-energy spectra of odd-mass and odd-odd nuclei. It is found that the calculated $\log{}_{10}ft$ values for the $\beta^+$ decays $^{68}$As$\to^{68}$Ge are particularly sensitive to the quadrupole-quadrupole boson interaction strength used for the parent ($^{68}$As) nucleus. We further incorporate higher-order terms in the one-nucleon transfer operators in the boson system, and find that, while their effects are non-negligible, they do not significantly alter qualitative features of $\beta$-decay properties. We report a novel application of the mapped IBM framework to compute $\beta$-decay half-lives, and show that the observed trend along isotopic chains are reasonably reproduced.

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arXiv2024

Parameter dependence of the $\beta$-decay properties of neutron-rich Zr isotopes within the interacting boson model

We investigate parameter dependence of the calculated $\beta$-decay properties, as well as low-lying states for the neutron-rich Zr isotopes within the neutron-proton interacting boson model (IBM-2) and interacting boson-fermion-fermion model (IBFFM-2). It is shown that the calculated $\log_{10}ft$ values for the transitions of the $0^+_1$ ground states of the parent even-even nuclei $^{96-102}$Zr into the $1^+_1$ states of the daughter odd-odd nuclei $^{96-102}$Nb consistently exhibit a strong dependence on those parameters associated with the quadrupole-quadrupole boson interaction, and with the residual interaction between an unpaired neutron and an unpaired proton in the IBFFM-2 Hamiltonian for the odd-odd Nb nuclei. By the reduction in magnitude of the quadrupole-quadrupole interaction strength by approximately a factor of 2, the calculated $\log_{10}ft$ values for the Zr$(0^+_1)\to$Nb$(1^+_1)$ transitions increase and agree with the experimental values. This points to a significant improvement over the previous study performed in the same mass region, that consists of the mapping from a relativistic energy density functional calculation onto the IBM-2 Hamiltonian.

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