Theory of Low-Energy Positron-Helium Scattering

A modified adiabatic method, previously tested in positron-hydrogen scattering, has been applied to the case of positron-helium scattering below the positronium threshold (17.8 eV). Since the ratio of the positron's velocity to that of the atomic electrons is about the same as in the hydrogen test case, similar accuracy is expected, the main source of error being the approximate atomic wave function used. Phase shifts for $L=0,1,2\mathrm{}$ are presented, and total and momentum-transfer cross sections are computed. The latter disagree completely with the only experiments performed to date.