Collisional effects on the HFS transitions of antiprotonic helium

Collisions of metastable antiprotonic helium with ordinary He atoms can induce transitions between hyperfine structure (HFS) sublevels and thus relaxation of the populations as well as shift and broadening of M1 microwave spectral lines. Previously we have considered these effects, using quantum close-coupling method for the collisions and the model interatomic interaction involving tensor term (Korenman and Yudin, J Phys B At Mol Opt Phys 39:1473–1484, 2006). In this paper we extend the consideration in two lines: (i) collisional transition rates, shifts and broadenings of M1-lines are considered in relation to the strength of the tensor interaction; (ii) time evolution of the density matrix of HFS states is considered using the generalized master equation with the calculated elementary characteristics. A good agreement with the recent experimental data on the time dependence of optimum signal-to-noise ratio and of linewidth is obtained using the strength of tensor interactions as a free parameter.