Calculation of spin-polarized positronium-helium $(2 {}^{3}S)$ and electron-helium $(2 {}^{3}S)$ scattering

Low-energy properties of spin-polarized electron-helium $\left(2{}^{3}S\right)$ and spin-polarized positronium-helium $\left(2{}^{3}S\right)$ scattering are calculated using the modified confined variational method. To take the van der Waals interaction into consideration, the van der Waals coefficient between positronium and helium $\left(2{}^{3}S\right)$ is calculated using the explicitly correlated Gaussian basis. Compared with the ground state noble gases, the larger scattering length and zero pickoff annihilation rate indicates that $\mathrm{He}\left(2{}^{3}S\right)$ may be a more suitable cooling gas. In the energy range we considered, no similarity is found for the $S$-wave cross sections between these two scatterings. A Ramsauer-Townsend minimum is observed in spin-polarized electron-helium$\left(2{}^{3}S\right)$ scattering due to the large polarization of metastable helium. This may open a new way to find and study the Ramsauer-Townsend effect.

Figure 1

$S$-wave cross sections of $\mathrm{sp}\text{−}e\text{−}{\mathrm{He}}^{*}$ and $\mathrm{sp}\text{−}\mathrm{Ps}\text{−}{\mathrm{He}}^{*}$ scattering. The momentum refers to the momentum of an electron or Ps, respectively.