Wave-packet analysis of multichannel resonances in positron scattering by a helium ion

We present the wave-packet analysis for two S -wave resonances in positron scattering by a helium ion whose existence was predicted by Bhatia and Drachman but has been controversial. The evolution of the wave packet is solved to exhibit temporary formation of the quasistationary state. For both the resonances, the position and width are determined through the resulting time delays in a consideration of a multichannel nature to agree with those by previous variational eigenenergy calculations. It is further found that the lower resonance dominantly forms from, and decays into, the n=2 states of the helium ion, while the higher one the n=3 states.