Hyperspherical coupled-channel calculations of positronium formation in low-energy positron-helium collisions

The hyperspherical coupled-channel method is applied to the positron-helium scatterings in a low-energy region below 54.4 eV. An independent electron model is used for the helium atom under the approximation that the active electron is bound by a central model potential. All the hyperspherical adiabatic states associated with Ps(n,l; n=1-4, l=0-2) and He(1snl; n=1-5, l=0-3) in the separated-atom limit are coupled for the expansion of the scattering equation, which is solved by means of a hybrid procedure of the diabatic-by-sector and the conventional adiabatic-basis-expansion methods. Excellent agreement is obtained with experiment for the positronium formation. © 1996 The American Physical Society.