We present results for medium-energy elastic, inelastic [transition to He(ls2ls), He(ls2lp), He(ls31s), and He(ls31p) states], capture [to Ps(ls), Ps(2s), and Ps(2p) states of the positronium (Ps) atom] and total cross sections of positronhelium scattering in the close coupling approach using realistic wave functions.
We studied low-and medium-energy positronhelium (e+-He) scattering in the eight state closecoupling approximation (CCA) including two dynamically active electrons and using realistic wave functions for the helium and positronium (Ps) atom states. Specifically, we calculated elastic, excitation and capture cross sections to the low-lying states of helium and Ps atoms. We included the following eight states in the CCA calculation: He(lsls), He(Is21s), He(ls21p), He(ls3ts), He(ls31p), Ps(Is), Ps(2s), and Ps(2p). We also found an S wave resonance at 19.267 eV of width 0.001 eV.
The CCA provides a practical framework for treating electron-atom and positron-atom scattering, which can in principle be improved upon by including more functions in the basis set, and it has been used extensively in e+-H [ 1-5] and positron-alkaliatom scattering [6,7]. It handles rearrangement and elastic channels in a unified way and provides results for excitation and positronium (Ps) formation at all energies. The positron-helium system is one of the simplest systems where the total capture cross section l John Simon Guggenheim Memorial Foundation Fellow.