Calculation of spin-polarized muonium-muonium and spin-polarized hydrogen-hydrogen scattering

In this paper, we investigate spin-polarized muonium-muonium and spin-polarized hydrogen-hydrogen scattering for total orbital angular momentum $L=0$ using the non-Born-Oppenheimer confined variational method combined with explicitly correlated Gaussian basis functions. Our approach yielded accurate $S$-wave phase shifts and elastic cross sections at scattering momenta below $0.6{a}_{0}^{\ensuremath{-}1}$, where ${a}_{0}$ is the Bohr radius. By utilizing the effective range formula, we determined the $S$-wave scattering lengths to be $3.70{a}_{0}$ and $1.35{a}_{0}$ for spin-polarized muonium-muonium and spin-polarized hydrogen-hydrogen scattering, respectively.