Near-threshold production of antihydrogen ion ( H ̄ + ) in positronium–antihydrogen collisions is predicted by a rigorous four-body scattering calculation. The convergence of the cross sections for the rearrangement and for all competing reactions (elastic scattering, de/excitation and de/polarization of positronium) is carefully examined against partial waves. The multi-channel scattering solutions are composed of functions that diagonalize the four-body Hamiltonian, and scattering functions that satisfy the correct asymptotic boundary conditions. The production rates of H ̄ + show large discrepancies compared to more approximate calculations.

Muon catalyzed fusion ( $$\mu$$μ CF) in which an elementary particle, muon, facilitates the nuclear fusion between the hydrogen isotopes has been investigated in a long history. In contrast to the rich theoretical and experimental information on the $$\mu$$μ CF in cold targets, there is relatively scarce information on the high temperature gas targets of deuterium-tritium mixture with high-thermal efficiency. We demonstrate new kinetics model of $$\mu$$μ CF including three roles of resonant muonic molecules, (i) changing isotopic population, (ii) producing epi-thermal muonic atoms, and (iii) inducing fusion in-flight. The new kinetics model reproduces experimental observations, showing higher cycle rate as the temperature increasing, over a wide range of target temperatures ( $$T<800$$T < 800 K) and tritium concentrations. Moreover, it can be tested by measurements of radiative dissociation X-rays around 2 keV. High energy-resolution X-ray detectors and intense muon beam which are recently available are suitable to reveal these dynamical mechanism of $$\mu$$μ CF cycles. Towards the future $$\mu$$μ CF experiments in the high-temperature gas target we have clarified the relationship between the fusion yield and density-temperature curve of adiabatic/shock-wave compression.

A highly charged muonic ion is a unique few-body atomic system where a negatively charged muon and a few electrons are simultaneously bound to a single nucleus. We report the first state-selective observation of highly charged muonic Ar (μAr) by electronic K x-ray spectroscopy using an array of transition-edge sensor microcalorimeters. The high-precision K x-ray spectra provide a clear signature of the presence of muonic atoms with one, two, and three electrons, i.e., H-like, He-like, and Li-like μAr. With the aid of theoretical calculations, we confirmed that the peak positions are consistent with the x-ray energies from highly charged Cl ions, and the intensities reflect deexcitation dynamics of highly charged μAr.

We report a theoretical calculation for the bound and S -wave resonance states of the positronic copper atom (e ⁺ Cu). A positron is a positively charged particle; therefore, a positronic atom has an attractive correlation between the positron and electron. A Gaussian expansion method is adopted to directly describe this correlation as well as the strong repulsive interaction with the nucleus. The correlation between the positron and electron is much more important than that between electrons in an analogous system of Cu ⁻ , although the formation of a positronium (Ps) in e ⁺ Cu is not expressed in the ground state structure explicitly. Resonance states are calculated with a complex scaling method and identified above the first excited state of the copper atom. Resonance states below Ps ( n = 2) + Cu ⁺ classified to a dipole series show agreement with a simple analytical law. Comparison of the resonance energies and widths of e ⁺ Cu with those of e ⁺ K, of which the potential energy of the host atom resembles that of e ⁺ Cu, reveals that the positions of the resonance for the e ⁺ Cu dipole series deviate equally from those of e ⁺ K.

Muon catalyzed fusion ($\mu \mathrm{CF}$) has recently regained considerable research interest owing to several new developments and applications. In this regard, we have performed a comprehensive study of the most important fusion reaction, namely, ${\left(dt\mu \right)}_{J=v=0}\to \alpha +n+\mu +17.6\mathrm{MeV}$ or ${\left(\alpha \mu \right)}_{nl}+n+17.6\mathrm{MeV}$. The coupled-channel Schrödinger equation for the reaction is thus solved, satisfying the boundary condition for the muonic molecule ${\left(dt\mu \right)}_{J=v=0}$ as the initial state and the outgoing wave in the $\alpha n\mu$ channel. We employ the $dt\mu$- and $\alpha n\mu$-channel coupled three-body model. All the nuclear interactions, the $d\text{−}t$ and $\alpha \text{−}n$ potentials, and the $dt\text{−}\alpha n$ channel-coupling nonlocal tensor potential are chosen to reproduce the observed low-energy ($1–300$ keV) astrophysical $S$ factor of the reaction $d+t\to \alpha +n+17.6\mathrm{MeV}$, as well as the total cross section of the $\alpha +n$ reaction at the corresponding energies. The resultant $dt\mu$ fusion rate is $1.15\times {10}^{12}{\mathrm{s}}^{-1}$. Substituting the obtained total wave function into the $T$ matrix based on the Lippmann-Schwinger equation, we have calculated absolute values of the fusion rates ${\lambda }_{\mathrm{f}}^{\mathrm{bound}}$ and ${\lambda }_{\mathrm{f}}^{\mathrm{cont}.}$ going to the bound and continuum states of the outgoing $\alpha \text{−}\mu$ pair, respectively. We then derived the initial $\alpha \text{−}\mu$ sticking probability ${\omega }_S^0={\lambda }_{\mathrm{f}}^{\mathrm{bound}}/({\lambda }_{\mathrm{f}}^{\mathrm{bound}}+{\lambda }_{\mathrm{f}}^{\mathrm{cont}.})=0.857\%$, which is $\approx 7\%$ smaller than the literature values $(\approx 0.91\%–0.93\%)$ and can explain the recent observations (2001) at high D-T densities. We have much improved the sticking-probability calculation by employing the $D$-wave $\alpha \text{−}n$ outgoing channel with the nonlocal tensor-force $dt\text{−}\alpha n$ coupling and by deriving ${\omega }_S^0$ based on the absolute values of the ${\lambda }_{\mathrm{f}}^{\mathrm{bound}}$ and ${\lambda }_{\mathrm{f}}^{\mathrm{cont}.}$. We also calculate the absolute values for the momentum and energy spectra of the muon emitted during the fusion process. The most important result is that the peak energy is 1.1 keV although the mean energy is 9.5 keV owing to the long higher-energy tail. This is an essential result for the ongoing experimental project to realize the generation of an ultraslow negative muon beam by utilizing the $\mu \mathrm{CF}$ for various applications, e.g., a scanning negative muon microscope and an injection source for the muon collider.