R-matrix calculation of antiproton capture by helium ions

Rigorous treatment is presented for antiproton capture by helium ions, i.e., p̅ +He⁺→(p̅ He⁺)^∗∗→p̅ He²⁺+e, by using R-matrix theory. The present work applies the R-matrix method to an exotic collision system containing an antiproton, a nucleus, and an electron. The eigenvalue problem in the R-matrix method is solved by the discrete-variable-representation algorithm without use of any decoupling approximation. The probability of antiproton capture is calculated for the total angular momentum J=30. A huge number of the overlapping resonances are found to be prominent everywhere over a wide range of energies. As suggested in a time-dependent wave-packet propagation calculation [ K. Sakimoto Phys. Rev. A 74 022709 (2006)], the resonances make a dominant contribution to the antiproton capture. It is found that the nonadiabatic coupling is always weak in off-resonance collisions, but can be very strong in resonance collisions.