Ps-He scattering below the first target excitation threshold

Scattering of a Pa atom off a He target has been investigated in the framework of the close-coupling approximation using two basis sets: (a) Ps(1s) + He(1s(2),1s2(1)s, 1s2(1)p) and (b) Ps(1s,2p) + He(1s(2),1s2(1)s,1s2(1)p). Target inelastic channels reduce the elastic cross sections appreciably near zero energy. The present results are in good agreement with the theoretical prediction of Drachman and Houston and the measured data of Canter, McNutt, and Roellig and Coleman et al. and are also in good agreement with the measured data of the UCL group from 15-20 eV.