Theoretical study of antiparticle collisions and exotic-atom formation

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(1) Positron scattering by atoms was studied by means of a large-scale hyperspherical close-coupling method. For the helium atom target we employ a mdel potential which reproduces the ionizaiton potential very accurately on the basis of the quasi single-electron atom approximaiton. All the adiabatic channel functions are coupled fully that are associated with the helium atomic states with n=1-4 and positronium states with n=1-5 in the separated -atom limit. The obtained formation cross sections agree well with the measured values and the present results are the bast among available theoretical values so far. In the case of electron scattering by positronium, hyperfine-structure transitions are studied including the spin-spin interactions explicitly. We also studied Feshbach-type resonances of the positronim negative-ion and tabulated systematically the energy shifts and widths in a wide energy region.(2) Formation of antiprotonic helium was studied in the collisions of antiproton with … More helium atoms and helium ions using a large-scale impact-parameter close-coupling method based on the pseudo state expansion. Highly excited states around n=38 are calculated accurately developing a new method for the decomposition of angular parts of wave functions. The energy eigenvalues and the life times of Auger decays agree excellently with measurements. The antiproton trapping in the first stage is analyzed representing ionization channles in terms of discretized pseudo continuum states. Proton-impact scattering was also calculated ststematically for comparison.(3) Muon transfer between hydrogen isotopes was studied in connection with the muon-catalyzed fusion reseach. The transfer cross sections from excited states are found to be larger than that from the ground state by several hundreds times. This is caused by the long-range interaction induced by the large dipole moment of the degenerate excited states. Feshbach-type resonaces are found and the cross sections are influenced considerably. Less