arXiv subjects

Masayasu Kamimura

Publications and source records attributed to Masayasu Kamimura.

10 recordsLinked to original sources

arXiv2025

Reaction processes of muon-catalyzed fusion in the muonic molecule $dd\mu$ studied with the tractable $T$-matrix model

Muon-catalyzed fusion has recently regained significant attention due to experimental and theoretical developments being performed. The present authors [Phys. Rev. C {\bf 109} 054625 (2024)] proposed the tractable $T$-matrix model based on the Lippmann-Schwinger equation to approximate the elaborate two- and three-body coupled-channel (CC) calculations [Kamimura, Kino, and Yamashita, Phys. Rev. C {\bf 107}, 034607 (2023)] for the nuclear reaction processes in the muonic molecule $dt\mu$, $(dt\mu)_{J=0} \to\!^4{\rm He} + n + \mu + 17.6 \, {\rm MeV}$. % or $(^4{\rm He}\mu)_{nl} + n + 17.6 \,{\rm MeV}$. The $T$-matrix model well reproduced almost all of the results generated by the CC work. In the present paper, we apply this model to the nuclear reaction processes in the $dd\mu$ molecule, $(dd\mu)_{J=1} \to\!^3{\rm He} + n + \mu +3.27 \,$ MeV or $t + p + \mu + 4.03 \,$ MeV, in which the fusion takes place via the $p$-wave $d$-$d$ relative motion. Recently, significantly different $p$-wave astrophysical $S(E)$ factors of the reaction $d + d \to\!^3{\rm He} + n$ or $t + p$ at $E \! \simeq \! 1$ keV to 1 MeV have been reported experimentally and theoretically by five groups. Employing many sets of nuclear interactions that can reproduce those five cases of $p$-wave $S(E)$ factors, we calculate the fusion rate of the $(dd\mu)_{J=1}$ molecule using three kinds of methods where results are consistent with each other. We also derive the $^3{\rm He}$-$\mu$ sticking probability and the absolute values of the energy and momentum spectra of the emitted muon. The violation of charge symmetry in the $p$-wave $d$-$d$ reaction and the $dd\mu$ fusion reaction is discussed. Information on the emitted 2.45-MeV neutrons and \mbox{1 keV-dominant} muons should be useful for the application of $dd\mu$ fusion.

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arXiv2024

Tractable $T$-matix model for reaction processes in muon catalyzed fusion $(dt\mu)_{J=v=0} \to \; \alpha + n + \mu + 17.6\, {\rm MeV} \; \mbox{or} \; (\alpha \mu)_{nl} + n +17.6 \,{\rm MeV}$

Reaction processes in muon catalyzed fusion ($\mu$CF), $(dt\mu)_{J=v=0} \to \alpha + n + \mu + 17.6\,{\rm MeV}\:$ or $ \;(\alpha \mu)_{nl} + n + 17.6\,{\rm MeV}$ in the D-T mixture was comprehensively studied by Kamimura, Kino and Yamashita [Phys. Rev. C 107, 034607 (2023)] by solving the $dt\mu$-$\alpha n\mu$ coupled channel (CC) Schr\"odinger equation under a boundary condition where the muonic molecule $(dt\mu)_{J=v=0}$ was set as the initial state and the outgoing wave was in the $\alpha n\mu$ channel. We approximate this CC framework and propose a considerably more tractable model using the $T$-matrix method based on the Lippmann-Schwinger equation. Nuclear interactions adopted in the $T$-matrix model are determined by reproducing the cross section of the reaction $d + t \to \alpha + n + 17.6\,{\rm MeV}$ at low energies. The cross section of the strong-coupling rearrangement reaction is presented in a simple closed form based on our new model. This $T$-matrix model have reproduced most of the calculated results on the above $\mu$CF reaction reported by Kamimura et al. (2023) and is applicable to other $\mu$CF systems such as $(dd\mu)$, $(tt\mu)$, $(dt\mu)^*$, $(dd\mu)^*$.

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arXiv2023

Derivation of transition density from the observed 4He(e,e')4He(0^+_2) form factor raising the alpha-particle monopole puzzle

Recently, the monopole transition form factor of the electron-scattering excitation of the 0^+_2 state (E_x=20.21 MeV) of the 4He nucleus was observed over a broad momentum transfer range (0.5 < q^2 < 5.0 fm^-2) with dramatically improved preision compared with older sets of data; modern nuclear forces, including those derived from the chiral effective field theory, failed to reproduce the form factor, which is called the alpha-particle monopole puzzle. To resolve this puzzle by improving the study of spatial structure of the 0^+_2 state, we derive in this letter a possible 0^+_1 --> 0^+_2 transition density \rho_tr(r) for r > 1 fm from the observed form factor. The shape of the transition density is significantly different from that obtained theoretically in the literature

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arXiv2018

Study of various few-body systems using Gaussian expansion method (GEM)

We review our calculation method, Gaussian expansion method (GEM), and its applications to various few-body (3- to 5-body) systems such as 1) few-nucleon systems, 2) few-body structure of hypernuclei, 3) clustering structure of light nuclei and unstable nuclei, 4) exotic atoms/molecules, 5) cold atoms, 6) nuclear astrophysics and 7) structure of exotic hadrons. Showing examples in our published papers, we explain i) high accuracy of GEM calculations and its reason, ii) wide applicability of GEM and iii) successful predictions by GEM calculations before measurements. GEM was proposed 30 years ago and has been applied to a variety of subjects. To solve few-body Schroedinger equations accurately, use is made of the Rayleigh-Ritz variational method for bound states, the complex-scaling method for resonant states and the Kohn-type variational principle to S-matrix for scattering states. The total wave function is expanded in terms of few-body Gaussian basis functions spanned over all the sets of rearrangement Jacobi coordinates. Gaussians with ranges in geometric progression work very well both for short-range and long-range behavior of the few-body wave functions. Use of Gaussians with complex ranges gives much more accurate solution when the wave function has many oscillations.

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arXiv2013

Complex-Scaling Calculation of Three-Body Resonances Using Complex-Range Gaussian Basis Functions --- Application to 3$α$ resonances in 12C ---

We propose to use the complex-range Gaussian basis functions, {r^l e^{-(1 \pm iω)(r/r_n)^2}Y_{lm}(\hat{r}); r_n in a geometric progression}, in the calculation of three-body resonances with the complex-scaling method (CSM) in which use is often made of the real-range Gaussian basis functions, {r^l e^{-(r/r_n)^2}Y_{lm}(\hat{r})}, that are suitable for describing the short-distance structure and the asymptotic decaying behavior of few-body systems. The former basis set is more powerful than the latter when describing the resonant and nonresonant continuum states with highly oscillating amplitude at large scaling angles θ. We applied the new basis functions to the CSM calculation of the 3αresonances with J=0^+, 2^+ and 4^+ in 12C. The eigenvalue distribution of the complex scaled Hamiltonian becomes more precise and the maximum scaling angle becomes drastically larger (θ_{max}=16 deg. \arrow 36 deg.) than those given by the use of the real-range Gaussians. Owing to these advantages, we were able to confirm the prediction by Kurokawa and Kato [Phys. Rev. C 71, 021301 (2005)] on the appearance of the new broad 0^+_3 state; we show it as an explicit resonance pole isolated from the 3$α$ continuum.

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arXiv2012

Stau-catalyzed d-t Nuclear Fusion

The gravitino of mass 10-100 GeV is a well motivated scenario in supergravity. If the stau is the next lightest supersymmetry particle, its life-time becomes order of $10^{6-8}$ sec. If it is the case the stau makes a big impact on the nuclear fusion, since it is a charged particle. In this paper we perform a detailed calculation of a stau-catalyzed d-t fusion. We find that if certain technical conditions are satisfied, it is not hopeless to use the nuclear fusion as a source of energy.

hep-ph↗

arXiv2009

Quantum three-body calculation of the nonresonant triple-αreaction rate at low temperatures

The triple-αreaction rate is re-evaluated by directly solving the three-body Schrödinger equation. The resonant and nonresonant processes are treated on the same footing using the continuum-discretized coupled-channels method for three-body scattering. Accurate description of the α-αnonresonant states significantly quenches the Coulomb barrier between the two-α's and the third αparticle. Consequently, the α-αnonresonant continuum states below the resonance at 92.04 keV, i.e., the ground state of 8Be, give markedly larger contribution at low temperatures than in foregoing studies. We show that Nomoto's method for three-body nonresonant capture processes, which is adopted in the NACRE compilation and many other studies, is a crude approximation of the accurate quantum three-body model calculation. We find about 20 orders-of-magnitude enhancement of the triple-αreaction rate around 10^7 K compared to the rate of NACRE.

astro-ph.SR↗

arXiv2009

Big-Bang Nucleosynthesis Reactions Catalyzed by a Long-Lived Negatively Charged Leptonic Particle

An accurate quantum three-body calculation is performed for the new type of big-bang nucleosynthesis (BBN) reactions that are catalyzed by a long-lived negatively-charged, massive leptonic particle (called X^-) such as the supersymmetric (SUSY) particle stau. The reactions studied here includes, i) 4He-transfer reactions such as (4He X)+d --> 6Li+X, ii) radiative capture reactions such as (7Be X)+ p --> (8B X) + gamma, iii) three-body breakup reactions such as (7Li X)+ p --> 4He+4He+X, iv) charge-exchange reactions such as (p X)+4He -->(4He X) +p, and v) neutron induced reactions such as (8Be X)+ n -->9Be+X, where (A X) denotes a Coulombic bound state of a nucleus A and X^-. In recent papers it has been claimed that some of the catalyzed BBN reactions have significantly large cross sections so as to markedly change the abundances of some elements, not only giving a solution to the 6Li-7Li problem (calculated underproduction of 6Li by a factor of 1000 and overproduction of 7Li+7Be by a factor of nearly 3) but also imposing strong restrictions on the lifetime and the primordial abundance of X^-. However, most of the calculations of these reaction cross sections in the literature were performed assuming too naive models or approximations that are unsuitable for the complicated low-energy nuclear reactions. We use a high-accuracy few-body calculational method developed by the authors, and provide precise cross sections and rates of these catalyzed BBN reactions for use in the BBN network calculation.

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arXiv2007

Four- and Five-Body Scattering Calculations

We study the five-quark system $uudd{\bar s}$ in the standard non-relativistic quark model by solving the scattering problem. Using the Gaussian Expansion Method (GEM), we perform the almost precise multi-quark calculations by treating a very large five-body modelspace including the NK scattering channel explicitly. Although a lot of pseudostates (discretized continuum states) with $J^π={1/2}^\pm$ and $J^π={3/2}^\pm$ are obtained within the bound-state approximation, all the states in $1.4-1.85$ GeV in mass around ${\rm {\rm Θ}}^+(1540)$ melt into non-resonant continuum states through the coupling with the NK scattering state in the realistic case, i.e., there is no five-quark resonance below 1.85GeV. Instead, we predict a five-quark resonance state of $J^π={1/2}^-$ with the mass of about 1.9GeV and the width of $Γ\simeq$ 2.68MeV. Similar calculation is done for the four-quark system $c{\bar c}q{\bar q}$ ($q=u,d$) in connection with X$^0$(3872).

hep-ph↗

arXiv2002

Determination of S17 from 7Be(d,n)8B reaction: CDCC analyses based on three-body model

The astrophysical factor $S_{17}$ for $^7$Be($p,γ$)$^8$B reaction is reliably extracted from the transfer reaction $^7$Be($d,n$)$^8$B at $E=7.5$ MeV with the asymptotic normalization coefficient method. The transfer reaction is accurately analyzed with CDCC based on the three-body model. This analysis is free from uncertainties of the optical potentials having been crucial in the previous DWBA analyses.

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