HYPERSPHERICAL CLOSE-COUPLING STUDY OF HYPERFINE TRANSITIONS IN LOW-ENERGY P-MU AND E(+(P)-)+PS SCATTERING/

We apply the hyperspherical close-coupling method to the elastic and s pin-hip processes in p + p mu and e(-) + Ps (or equivalently, e(+) + P s) scattering at low collision energies. The spin-spin interactions V- S are included explicitly in the Hamiltonian, producing the correct hy perfine-splitting energy Delta epsilon in the separated-atom limit. A comparison is made with a simpler method in which the effect of V-S is represented only by the symmetry of the wave functions with respect t o the interchange of the two identical particles. Explicit inclusion o f V-S is found to be of vital importance for the calculation of the sp in-flip cross sections for collision energies lower than Delta epsilon for both p + p mu and e(-)(e(+))+Ps collisions. The elastic cross sec tions are less sensitive to V-S, but those for p + p mu are still affe cted by V-S for collision energies lower th an Delta epsilon. [S1050-2 947(98)00908-1]